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Arbitrary file write when scanning a specially-crafted remote PyPI package

Moderate
christophetd published GHSA-78m5-jpmf-ch7v Dec 5, 2022

Package

pip guarddog (pip)

Affected versions

<v0.1.7

Patched versions

v0.1.8

Description

Summary

Unsafe extracting using shutil.unpack_archive() from a remotely retrieved tarball may lead to writing the extracted file to an unintended destination.

Details

Extracting files using shutil.unpack_archive() from a potentially malicious tarball without validating that the destination file path is within the intended destination directory can cause files outside the destination directory to be overwritten.

The vulnerable code snippet is between L153..158.

response = requests.get(url, stream=True)

with open(zippath, "wb") as f:
      f.write(response.raw.read())

shutil.unpack_archive(zippath, unzippedpath)

It seems that a remotely retrieved tarball which could be with the extension .tar.gz happens to be unpacked using shutil.unpack_archive() with no destination verification/limitation of the extracted files.

PoC

The PoC provided showcases the risk of extracting the non-harmless text file sim4n6.txt to a parent location rather than the current folder.

> tar --list -f archive.tar
tar: Removing leading `../../../' from member names
../../../sim4n6.txt

> python3 
Python 3.10.6 (main, Nov  2 2022, 18:53:38) [GCC 11.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import shutil
>>> shutil.unpack_archive("archive.tar")
>>> exit()

> file ../../../sim4n6.txt
../../../sim4n6.txt: ASCII text

A Potential Attack Scenario

  • An attacker may craft a malicious tarball with a filename path, such as ../../../../../../../../etc/passwd, and then serve the archive remotely, thus, providing a possibility to overwrite the system files.

Mitigation

Potential mitigation could be to:

  • Use a safer module, like zipfile.
  • Validate the location of the extracted files and discard those with malicious paths such as a relative path .. or absolute ones.

Severity

Moderate
5.8
/ 10

CVSS base metrics

Attack vector
Network
Attack complexity
High
Privileges required
None
User interaction
Required
Scope
Changed
Confidentiality
Low
Integrity
Low
Availability
Low
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:L/A:L

CVE ID

CVE-2022-23530

Weaknesses

Credits