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

⚠️ This issue respects the following points: ⚠️

• This is a bug, not a question or a configuration/webserver/proxy issue.
• This issue is not already reported on Github OR Nextcloud Community Forum (I've searched it).
• Nextcloud Server is up to date. See Maintenance and Release Schedule for supported versions.
• I agree to follow Nextcloud's 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
   
2. Setup davfs2 and a mount unit with the share credentials (share handle is the path suffix of the share URL):

   $ 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

   $ systemctl daemon-reload && systemctl start run-test.mount
   

4. Verify it is mounted and reading works

   $ cat /run/test/some-test-file.txt
   

5. Attempt to upload a new file

   $ 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?

• Default user-backend (database)
• LDAP/ Active Directory
• SSO - SAML
• Other

Configuration report

{
    "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

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

No errors have been found.

Nextcloud Logs

Lots of (potentially related):

{
    "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:

{
    "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:///public.php/webdav instead of https:///public.php/dav/files/ - neither of which works since the update to NC 34.

Start with apps/files_lock/lib/DAV/LockBackend.php, named in the SessionNotAvailableException trace, and reproduce the write through the public WebDAV endpoint using davfs2. Compare the LOCK request and the browser upload path, then trace the session failure. Done means writing a file through a read/write public share succeeds without the exception.