[Bug]: SessionNotAvailableException when attempting to write files from a link share over webdav

### ⚠️ This issue respects the following points: ⚠️

- [x] This is a **bug**, not a question or a configuration/webserver/proxy issue.
- [x] This issue is **not** already reported on [Github](https://github.com/nextcloud/server/issues?q=is%3Aopen+is%3Aissue+label%3Abug) OR [Nextcloud Community Forum](https://help.nextcloud.com/) _(I've searched it)_.
- [x] Nextcloud Server **is** up to date. See [Maintenance and Release Schedule](https://github.com/nextcloud/server/wiki/Maintenance-and-Release-Schedule) for supported versions.
- [x] I agree to follow Nextcloud's [Code of Conduct](https://nextcloud.com/contribute/code-of-conduct/).

### Bug description

I am attempting to mount a public share via davfs2. Mounting works, reading works, but when attempting to write to the share, I get an input/output error in davfs2 and a `OCP\Session\Exceptions\SessionNotAvailableException` on Nextcloud's side.

Writing is enabled in the share permissions and works without issues when accessing the share via browser (tested by uploading the same file I couldnt write via davfs2).

### Steps to reproduce

1. Create a public share, configure it to allow read/write
   <img width="300" alt="Image" src="https://github.com/user-attachments/assets/f0d5001f-f37d-48f8-8750-49ab8595f937" />
2. Setup davfs2 and a mount unit with the share credentials (share handle is the path suffix of the share URL):
   ```bash
   $ cat /etc/davfs2/secrets
   /run/test <share-handle> ""
   $ systemctl cat run-test.mount
   [Unit]
   Before=remote-fs.target umount.target
   Conflicts=umount.target
   After=network-online.target


   [Mount]
   What=https://<nextcloud-domain>/public.php/dav/files/<share-handle>
   Where=/run/test
   Type=davfs
   TimeoutSec=30s
   Options=defaults,uid=1000,grpid,file_mode=0660,x-systemd.automount,x-systemd.mount-timeout=30,_netdev

   [Install]
   WantedBy=multi-user.target
   ```
3. Mount the share
   ```sh
   $ systemctl daemon-reload && systemctl start run-test.mount
   ```
4. Verify it is mounted and reading works
   ```sh
   $ cat /run/test/some-test-file.txt
   ```
5. Attempt to upload a new file
   ```sh
   $ cp ./new-file.txt /run/test/new-file.txt
   cp: cannot create regular file '/run/media/tobias/keepass/personal_accounts.kdbx': Input/output error
   ```


### Expected behavior

When a share is configured accordingly, reading and writing should work via webdav.

### Nextcloud Server version

34

### Operating system

Debian/Ubuntu

### PHP engine version

PHP 8.5

### Web server

Apache (supported)

### Database engine version

MySQL

### Is this bug present after an update or on a fresh install?

Upgraded to a MAJOR version (ex. 31 to 32)

### Are you using the Nextcloud Server Encryption module?

Encryption is Disabled

### What user-backends are you using?

- [x] Default user-backend _(database)_
- [ ] LDAP/ Active Directory
- [ ] SSO - SAML
- [ ] Other

### Configuration report

```json
{
    "system": {
        "passwordsalt": "***REMOVED SENSITIVE VALUE***",
        "secret": "***REMOVED SENSITIVE VALUE***",
        "trusted_domains": {
            "0": "localhost",
            "5": "nextcloudpi.local",
            "1": "192.168.178.31",
            "7": "nextcloudpi",
            "8": "nextcloudpi.lan",
            "2": "***REMOVED SENSITIVE VALUE***",
            "11": "***REMOVED SENSITIVE VALUE***",
            "12": "***REMOVED SENSITIVE VALUE***",
            "14": "nextcloudpi",
            "3": "***REMOVED SENSITIVE VALUE***",
            "22": "***REMOVED SENSITIVE VALUE***",
        },
        "datadirectory": "***REMOVED SENSITIVE VALUE***",
        "overwrite.cli.url": "***REMOVED SENSITIVE VALUE***",
        "dbtype": "mysql",
        "version": "34.0.2.1",
        "dbname": "***REMOVED SENSITIVE VALUE***",
        "dbhost": "***REMOVED SENSITIVE VALUE***",
        "dbport": "",
        "dbtableprefix": "oc_",
        "mysql.utf8mb4": true,
        "dbuser": "***REMOVED SENSITIVE VALUE***",
        "dbpassword": "***REMOVED SENSITIVE VALUE***",
        "installed": true,
        "instanceid": "***REMOVED SENSITIVE VALUE***",
        "memcache.local": "\\OC\\Memcache\\Redis",
        "memcache.locking": "\\OC\\Memcache\\Redis",
        "redis": {
            "host": "***REMOVED SENSITIVE VALUE***",
            "port": 0,
            "timeout": 0,
            "password": "***REMOVED SENSITIVE VALUE***"
        },
        "tempdirectory": "\/mnt\/ncp\/ncdata\/data\/tmp",
        "mail_smtpmode": "smtp",
        "mail_smtpauthtype": "LOGIN",
        "mail_from_address": "***REMOVED SENSITIVE VALUE***",
        "mail_domain": "***REMOVED SENSITIVE VALUE***",
        "mail_template_class": "\\OCA\\EmailTemplates\\EmailTemplate",
        "overwriteprotocol": "https",
        "theme": "",
        "loglevel": 2,
        "maintenance": false,
        "logfile": "\/mnt\/ncp\/ncdata\/data\/nextcloud.log",
        "mail_sendmailmode": "smtp",
        "log_type": "file",
        "jpeg_quality": 60,
        "data-fingerprint": "027045aed0be1491c6126ef8507a9599",
        "app_install_overwrite": {
            "0": "end_to_end_encryption",
            "1": "twofactor_yubikey",
            "2": "social",
            "3": "whiteboard",
            "5": "nextcloudpi",
            "7": "maps",
            "8": "memories"
        },
        "auth.bruteforce.protection.enabled": false,
        "mail_smtpauth": true,
        "mail_smtphost": "***REMOVED SENSITIVE VALUE***",
        "mail_smtpport": "587",
        "mail_smtpname": "***REMOVED SENSITIVE VALUE***",
        "mail_smtppassword": "***REMOVED SENSITIVE VALUE***",
        "trusted_proxies": "***REMOVED SENSITIVE VALUE***",
        "default_phone_region": "DE",
        "filelocking": true,
        "preview_max_x": 2048,
        "preview_max_y": 2048,
        "preview_imaginary_url": "***REMOVED SENSITIVE VALUE***",
        "enabledPreviewProviders": [
            "OC\\Preview\\BMP",
            "OC\\Preview\\GIF",
            "OC\\Preview\\JPEG",
            "OC\\Preview\\MarkDown",
            "OC\\Preview\\MP3",
            "OC\\Preview\\PNG",
            "OC\\Preview\\TXT",
            "OC\\Preview\\XBitmap",
            "OC\\Preview\\OpenDocument",
            "OC\\Preview\\Krita",
            "OC\\Preview\\Image",
            "OC\\Preview\\Movie"
        ],
        "memories.exiftool": "\/var\/www\/nextcloud\/apps\/memories\/exiftool-bin\/exiftool-aarch64-glibc",
        "memories.vod.path": "\/var\/www\/nextcloud\/apps\/memories\/bin-ext\/go-vod-amd64",
        "memories.exiftool_no_local": true,
        "memories.vod.ffmpeg": "\/usr\/bin\/ffmpeg",
        "memories.vod.ffprobe": "\/usr\/bin\/ffprobe",
        "has_rebuilt_cache": true,
        "maintenance_window_start": 2,
        "memories.db.triggers.fcu": true,
        "memories.gis_type": 1,
        "defaultapp": "files,dashboard",
        "files.chunked_upload.max_size": 1073741824,
        "serverid": 135,
        "openmetrics_allowed_clients": [
            "0.0.0.0\/0"
        ],
        "allow_local_remote_servers": false
    }
}
```

### List of activated Apps

```shell
Enabled:
  - activity: 7.0.0
  - admin_audit: 1.24.0
  - announcementcenter: 7.4.1
  - app_api: 34.0.0
  - appointments: 2.7.4
  - appstore: 1.0.0
  - assistant: 3.5.0
  - attendance: 1.42.0
  - audioplayer: 3.9.0
  - bookmarks: 16.2.4
  - bruteforcesettings: 7.0.0
  - calendar: 6.5.2
  - circles: 34.0.0
  - cloud_federation_api: 1.18.0
  - collectives: 4.4.2
  - comments: 1.24.0
  - contacts: 8.7.5
  - contactsinteraction: 1.15.0
  - context_chat: 5.4.0
  - cookbook: 0.11.9
  - cospend: 4.0.2
  - dashboard: 7.14.0
  - dav: 1.39.0
  - dav_push: 1.0.2
  - deck: 1.18.3
  - event_update_notification: 2.9.0
  - external: 9.0.1
  - federatedfilesharing: 1.24.0
  - federation: 1.24.0
  - files: 2.6.0
  - files_automatedtagging: 5.0.0
  - files_downloadlimit: 5.2.0
  - files_external: 1.26.0
  - files_lock: 34.0.1
  - files_pdfviewer: 7.0.0-dev.0
  - files_reminders: 1.7.0
  - files_sharing: 1.26.0
  - files_trashbin: 1.24.0
  - files_versions: 1.27.0
  - firstrunwizard: 7.0.0-dev.0
  - forms: 5.3.5
  - gpoddersync: 3.17.0
  - group_everyone: 0.1.20
  - impersonate: 5.0.0
  - integration_openai: 4.5.2
  - integration_paperless: 1.0.13
  - logreader: 7.0.0
  - lookup_server_connector: 1.22.0
  - maps: 1.7.1
  - memories: 8.1.0
  - music: 3.1.1
  - musicsheetviewer: 1.3.1
  - nextcloud_announcements: 6.0.0
  - nextcloudpi: 0.0.2
  - notes: 6.0.1
  - notifications: 7.0.0-dev.1
  - notify_push: 1.3.5
  - oauth2: 1.22.0
  - office: 1.0.0
  - password_policy: 6.0.0-dev.0
  - phonetrack: 1.3.2
  - photos: 7.0.0
  - polls: 9.1.4
  - previewgenerator: 5.14.0
  - privacy: 6.0.0-dev.1
  - profile: 1.3.0
  - provisioning_api: 1.24.0
  - qownnotesapi: 26.5.0
  - recognize: 12.0.0
  - recommendations: 7.0.0
  - registration: 3.0.0
  - related_resources: 5.0.0-dev.0
  - richdocuments: 11.1.0
  - richdocumentscode: 26.4.104
  - secrets: 3.0.5
  - serverinfo: 6.0.0
  - settings: 1.17.0
  - sharebymail: 1.24.0
  - side_menu: 6.0.1
  - spreed: 24.0.3
  - survey_client: 6.0.0-dev.0
  - systemtags: 1.24.0
  - tables: 2.2.1
  - tasks: 0.18.1
  - text: 8.0.0
  - text_templates: 1.5.0
  - theming: 2.9.0
  - twofactor_backupcodes: 1.23.0
  - twofactor_nextcloud_notification: 8.0.0
  - twofactor_totp: 16.0.0
  - twofactor_webauthn: 2.7.0
  - user_status: 1.14.0
  - viewer: 7.0.0-dev.0
  - weather_status: 1.14.0
  - webhook_listeners: 1.6.0
  - whiteboard: 1.5.9
  - workflowengine: 2.16.0
Disabled:
  - camerarawpreviews: 1.1.2 (installed 1.1.2)
  - drawio: 4.3.5 (installed 4.3.5)
  - encryption: 2.22.0
  - files_3dmodelviewer: 0.0.18 (installed 0.0.18)
  - files_fulltextsearch: 33.0.0 (installed 33.0.0)
  - files_fulltextsearch_tesseract: 32.0.0 (installed 32.0.0)
  - fulltextsearch: 33.0.0 (installed 33.0.0)
  - fulltextsearch_elasticsearch: 33.0.0 (installed 33.0.0)
  - fulltextsearch_opensearch: 0.0.1 (installed 0.0.1)
  - google_synchronization: 4.2.0 (installed 4.2.0)
  - integration_giphy: 2.2.1 (installed 2.2.1)
  - keeweb: 0.6.26 (installed 0.6.26)
  - libresign: 14.1.0 (installed 14.1.0)
  - nextpod: 0.7.11 (installed 0.7.11)
  - support: 6.0.0 (installed 1.0.0)
  - suspicious_login: 12.0.0-dev.0
  - testing: 1.23.0
  - thesearchpage: 2.4.3 (installed 2.4.3)
  - updatenotification: 1.24.0 (installed 1.11.0)
  - user_ldap: 1.25.0
```

### Nextcloud Signing status

```shell
No errors have been found.
```

### Nextcloud Logs

Lots of (potentially related):
```json
{
    "reqId": "amxenYeakDRb0N1uRUhaWwAAAwo",
    "level": 2,
    "time": "2026-07-31T08:36:45+00:00",
    "remoteAddr": "2a02:3102:8420:4a0:90fe:baff:fe88:40ff",
    "user": "--",
    "app": "PHP",
    "method": "PROPFIND",
    "url": "/public.php/webdav/<some-path>/.nomemories",
    "scriptName": "/public.php",
    "message": "Cannot modify header information - headers already sent by (output started at /var/www/nextcloud/3rdparty/sabre/http/lib/Message.php:117) at /var/www/nextcloud/3rdparty/sabre/http/lib/Sapi.php#68",
    "userAgent": "sabre-dav/4.7.0 (http://sabre.io/)",
    "version": "34.0.2.1",
    "data": {
        "app": "PHP"
    }
}
```

And this is the actual error when attempting to write the file:
```json
{
    "reqId": "amxTDboSsHG29mnH745i7QAAURg",
    "level": 3,
    "time": "2026-07-31T07:47:25+00:00",
    "remoteAddr": "2a02:8106:1ea:8000:abe3:638d:62fc:917c",
    "user": "--",
    "app": "webdav",
    "method": "LOCK",
    "url": "/public.php/webdav/qt_temp.BeKoQI",
    "scriptName": "/public.php",
    "message": "Exception thrown: OCP\\Session\\Exceptions\\SessionNotAvailableException",
    "userAgent": "davfs2/1.7.3 neon/0.37.1",
    "version": "34.0.2.1",
    "exception": {
        "Exception": "OCP\\Session\\Exceptions\\SessionNotAvailableException",
        "Message": "",
        "Code": 0,
        "Trace": [
            {
                "file": "/var/www/nextcloud/apps/files_lock/lib/DAV/LockBackend.php",
                "line": 124,
                "function": "getFileFromUri",
                "class": "OCA\\FilesLock\\Service\\FileService",
                "type": "->"
            },
            {
                "file": "/var/www/nextcloud/apps/files_lock/lib/DAV/LockBackend.php",
                "line": 68,
                "function": "getFileFromUri",
                "class": "OCA\\FilesLock\\DAV\\LockBackend",
                "type": "->"
            },
            {
                "file": "/var/www/nextcloud/3rdparty/sabre/dav/lib/DAV/Locks/Plugin.php",
                "line": 322,
                "function": "lock",
                "class": "OCA\\FilesLock\\DAV\\LockBackend",
                "type": "->"
            },
            {
                "file": "/var/www/nextcloud/3rdparty/sabre/dav/lib/DAV/Locks/Plugin.php",
                "line": 236,
                "function": "lockNode",
                "class": "Sabre\\DAV\\Locks\\Plugin",
                "type": "->"
            },
            {
                "file": "/var/www/nextcloud/apps/files_lock/lib/DAV/LockPlugin.php",
                "line": 218,
                "function": "httpLock",
                "class": "Sabre\\DAV\\Locks\\Plugin",
                "type": "->"
            },
            {
                "file": "/var/www/nextcloud/3rdparty/sabre/event/lib/WildcardEmitterTrait.php",
                "line": 89,
                "function": "httpLock",
                "class": "OCA\\FilesLock\\DAV\\LockPlugin",
                "type": "->"
            },
            {
                "file": "/var/www/nextcloud/3rdparty/sabre/dav/lib/DAV/Server.php",
                "line": 472,
                "function": "emit",
                "class": "Sabre\\DAV\\Server",
                "type": "->"
            },
            {
                "file": "/var/www/nextcloud/apps/dav/lib/Connector/Sabre/Server.php",
                "line": 215,
                "function": "invokeMethod",
                "class": "Sabre\\DAV\\Server",
                "type": "->"
            },
            {
                "file": "/var/www/nextcloud/apps/dav/appinfo/v1/publicwebdav.php",
                "line": 136,
                "function": "start",
                "class": "OCA\\DAV\\Connector\\Sabre\\Server",
                "type": "->"
            },
            {
                "file": "/var/www/nextcloud/public.php",
                "line": 90,
                "args": [
                    "/var/www/nextcloud/apps/dav/appinfo/v1/publicwebdav.php"
                ],
                "function": "require_once"
            }
        ],
        "File": "/var/www/nextcloud/apps/files_lock/lib/Service/FileService.php",
        "Line": 85,
        "message": "",
        "exception": "{\"class\":\"OCP\\Session\\Exceptions\\SessionNotAvailableException\",\"message\":\"\",\"code\":0,\"file\":\"/var/www/nextcloud/apps/files_lock/lib/Service/FileService.php:85\",\"trace\":\"#0 /var/www/nextcloud/apps/files_lock/lib/DAV/LockBackend.php(124): OCA\\FilesLock\\Service\\FileService->getFileFromUri()\\n#1 /var/www/nextcloud/apps/files_lock/lib/DAV/LockBackend.php(68): OCA\\FilesLock\\DAV\\LockBackend->getFileFromUri()\\n#2 /var/www/nextcloud/3rdparty/sabre/dav/lib/DAV/Locks/Plugin.php(322): OCA\\FilesLock\\DAV\\LockBackend->lock()\\n#3 /var/www/nextcloud/3rdparty/sabre/dav/lib/DAV/Locks/Plugin.php(236): Sabre\\DAV\\Locks\\Plugin->lockNode()\\n#4 /var/www/nextcloud/apps/files_lock/lib/DAV/LockPlugin.php(218): Sabre\\DAV\\Locks\\Plugin->httpLock()\\n#5 /var/www/nextcloud/3rdparty/sabre/event/lib/WildcardEmitterTrait.php(89): OCA\\FilesLock\\DAV\\LockPlugin->httpLock()\\n#6 /var/www/nextcloud/3rdparty/sabre/dav/lib/DAV/Server.php(472): Sabre\\DAV\\Server->emit()\\n#7 /var/www/nextcloud/apps/dav/lib/Connector/Sabre/Server.php(215): Sabre\\DAV\\Server->invokeMethod()\\n#8 /var/www/nextcloud/apps/dav/appinfo/v1/publicwebdav.php(136): OCA\\DAV\\Connector\\Sabre\\Server->start()\\n#9 /var/www/nextcloud/public.php(90): require_once('...')\\n#10 {main}\"}",
        "CustomMessage": "Exception thrown: OCP\\Session\\Exceptions\\SessionNotAvailableException"
    }
}
```

### Additional info

This setup worked with Nextcloud up to 33, albeit using the (old?) endpoint https://<nextcloud-url>/public.php/webdav instead of https://<nextcloud-url>/public.php/dav/files/<share-handle> - neither of which works since the update to NC 34.

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

Uh oh!

[Bug]: SessionNotAvailableException when attempting to write files from a link share over webdav #62719

⚠️ This issue respects the following points: ⚠️

Bug description

Steps to reproduce

Expected behavior

Nextcloud Server version

Operating system

PHP engine version

Web server

Database engine version

Is this bug present after an update or on a fresh install?

Are you using the Nextcloud Server Encryption module?

What user-backends are you using?

Configuration report

List of activated Apps

Nextcloud Signing status

Nextcloud Logs

Additional info

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Uh oh!

Uh oh!

[Bug]: SessionNotAvailableException when attempting to write files from a link share over webdav #62719

Description

⚠️ This issue respects the following points: ⚠️

Bug description

Steps to reproduce

Expected behavior

Nextcloud Server version

Operating system

PHP engine version

Web server

Database engine version

Is this bug present after an update or on a fresh install?

Are you using the Nextcloud Server Encryption module?

What user-backends are you using?

Configuration report

List of activated Apps

Nextcloud Signing status

Nextcloud Logs

Additional info

Metadata

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Issue actions