[Bug]: Reshare a file shared from a remote server error User not found in backend

⚠️ 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

When trying to reshare (by link or to an user) a file in a folder shared by another NC instance to my user lead to an error 500 when create the share and NoUserException User not found in backend.
The share is created anyway but try to access to the file lead to the same error.

Steps to reproduce

1. Share a folder to a remote account, from a NC instance 1 to instance 2, with the reshare right.
2. On the instance 2, try to share a file in this folder to a user of the instance 2 or by link
3. See the error 500 in the console log Bug from Maps app https://github.com/nextcloud/maps/issues/1427
4. Try to access to the file by the shale link
5. See the error in the NC log

Expected behavior

Can access to the shared file.

Nextcloud Server version

30

Operating system

Debian/Ubuntu

PHP engine version

PHP 8.2

Web server

Nginx

Database engine version

MariaDB

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

None

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": {
        "instanceid": "***REMOVED SENSITIVE VALUE***",
        "passwordsalt": "***REMOVED SENSITIVE VALUE***",
        "secret": "***REMOVED SENSITIVE VALUE***",
        "trusted_proxies": "***REMOVED SENSITIVE VALUE***",
        "forwarded_for_headers": [
            "HTTP_X_FORWARDED_FOR"
        ],
        "trusted_domains": [
            "cloud.lebib.org",
            "nuage.lebib.org",
            "claude.lebib.org",
            "bib-cloud.lebib.lan",
            "bib-cloud",
            "10.13.208.6"
        ],
        "datadirectory": "***REMOVED SENSITIVE VALUE***",
        "dbtype": "mysql",
        "version": "30.0.12.2",
        "dbname": "***REMOVED SENSITIVE VALUE***",
        "dbhost": "***REMOVED SENSITIVE VALUE***",
        "dbtableprefix": "oc_",
        "dbuser": "***REMOVED SENSITIVE VALUE***",
        "dbpassword": "***REMOVED SENSITIVE VALUE***",
        "default_language": "fr",
        "installed": true,
        "mail_from_address": "***REMOVED SENSITIVE VALUE***",
        "mail_smtpmode": "smtp",
        "mail_domain": "***REMOVED SENSITIVE VALUE***",
        "htaccess.RewriteBase": "\/",
        "enable_previews": true,
        "preview_max_x": 2048,
        "preview_max_scale_factor": 1,
        "log_type": "file",
        "syslog_tag": "NextCloud",
        "loglevel": 3,
        "logfile": "\/var\/log\/nextcloud\/nextcloud.log",
        "log_query": false,
        "updater.release.channel": "stable",
        "allow_user_to_change_display_name": true,
        "memcache.local": "\\OC\\Memcache\\APCu",
        "memcache.distributed": "\\OC\\Memcache\\Redis",
        "memcache.locking": "\\OC\\Memcache\\Redis",
        "redis": {
            "host": "***REMOVED SENSITIVE VALUE***",
            "port": 6379
        },
        "mysql.utf8mb4": true,
        "mail_sendmailmode": "smtp",
        "mail_smtphost": "***REMOVED SENSITIVE VALUE***",
        "mail_smtpport": "465",
        "cache_chunk_gc_ttl": 86400,
        "default_phone_region": "FR",
        "maintenance": false,
        "overwrite.cli.protocol": "https",
        "overwrite.cli.url": "https:\/\/cloud.lebib.org",
        "webhooks_calendar_object_created_url": "https:\/\/framagit.org\/api\/v4\/projects\/84144\/ref\/main\/trigger\/pipeline?token=glptt-36bc1bc933dc7e9dedf9397010a39993067899bf",
        "mail_smtpdebug": false,
        "debug": false,
        "mail_smtpsecure": "ssl",
        "mail_smtpstreamoptions": {
            "ssl": {
                "allow_self_signed": true,
                "verify_peer": false,
                "verify_peer_name": false
            }
        },
        "profiler": false,
        "app_install_overwrite": [
            "files_rightclick",
            "issuetemplate",
            "apporder",
            "metadata",
            "calendar_news",
            "side_menu",
            "files_trackdownloads"
        ],
        "maintenance_window_start": 2
    }
}

List of activated Apps

- activity: 3.0.0
  - announcementcenter: 7.1.3
  - app_api: 4.0.6
  - bruteforcesettings: 3.0.0
  - calendar: 5.3.3
  - calendar_resource_management: 0.9.0
  - circles: 30.0.0
  - cloud_federation_api: 1.13.0
  - collectives: 2.18.0
  - comments: 1.20.1
  - contacts: 7.1.3
  - contactsinteraction: 1.11.0
  - cospend: 3.0.11
  - dashboard: 7.10.0
  - data_request: 2.0.1
  - dav: 1.31.1
  - deck: 1.14.5
  - drawio: 3.0.9
  - drop_account: 2.7.1
  - federatedfilesharing: 1.20.0
  - federation: 1.20.0
  - files: 2.2.0
  - files_downloadlimit: 3.0.0
  - files_external: 1.22.0
  - files_pdfviewer: 3.0.0
  - files_reminders: 1.3.0
  - files_sharing: 1.22.0
  - files_trashbin: 1.20.1
  - files_versions: 1.23.0
  - fileslibreofficeedit: 2.0.1
  - firstrunwizard: 3.0.0
  - forms: 5.1.0
  - groupfolders: 18.1.2
  - impersonate: 1.17.1
  - integration_dropbox: 3.1.0
  - integration_gitlab: 3.2.0
  - integration_google: 3.2.0
  - integration_openstreetmap: 2.1.0
  - intros: 1.1.2
  - keeweb: 0.6.21
  - logreader: 3.0.0
  - lookup_server_connector: 1.18.0
  - maps: 1.5.0
  - nextcloud_announcements: 2.0.0
  - notifications: 3.0.0
  - notify_push: 1.1.0
  - oauth2: 1.18.1
  - password_policy: 2.0.0
  - photos: 3.0.2
  - polls: 7.4.4
  - privacy: 2.0.0
  - provisioning_api: 1.20.0
  - quota_warning: 1.21.0
  - recommendations: 3.0.0
  - registration: 2.7.0
  - related_resources: 1.5.0
  - serverinfo: 2.0.0
  - settings: 1.13.0
  - sharebymail: 1.20.0
  - side_menu: 4.1.1
  - spreed: 20.1.7
  - survey_client: 2.0.0
  - suspicious_login: 8.0.0
  - systemtags: 1.20.0
  - tables: 0.9.3
  - tasks: 0.16.1
  - text: 4.1.0
  - theming: 2.6.0
  - theming_customcss: 1.18.0
  - timemanager: 0.3.18
  - twofactor_backupcodes: 1.19.0
  - updatenotification: 1.20.0
  - uppush: 2.3.0
  - user_status: 1.10.0
  - viewer: 3.0.0
  - weather_status: 1.10.0
  - webhook_listeners: 1.1.0-dev
  - workflow_ocr: 1.30.1
  - workflowengine: 2.12.0

Nextcloud Signing status

Nextcloud Logs

{"reqId":"lBZWe1y7fJe9sGal0rtZ","level":3,"time":"2025-06-18T20:14:45+00:00","remoteAddr":"10.12.200.200","user":"--","app":"webdav","method":"PROPFIND","url":"/public.php/dav/files/MLMyaZttBjzow8m/","message":"User not found in backend","userAgent":"Mozilla/5.0 (X11; Linux x86_64; rv:138.0) Gecko/20100101 Firefox/138.0","version":"30.0.12.2","exception":{"Exception":"OC\\User\\NoUserException","Message":"User not found in backend","Code":0,"Trace":[{"file":"/srv/nextcloud/lib/private/User/LazyUser.php","line":124,"function":"getUser","class":"OC\\User\\LazyUser","type":"->"},{"file":"/srv/nextcloud/lib/private/Accounts/AccountManager.php","line":542,"function":"getEMailAddress","class":"OC\\User\\LazyUser","type":"->"},{"file":"/srv/nextcloud/lib/private/Accounts/AccountManager.php","line":202,"function":"buildDefaultUserRecord","class":"OC\\Accounts\\AccountManager","type":"->"},{"file":"/srv/nextcloud/lib/private/Accounts/AccountManager.php","line":648,"function":"getUser","class":"OC\\Accounts\\AccountManager","type":"->"},{"file":"/srv/nextcloud/apps/dav/lib/Connector/Sabre/FilesPlugin.php","line":373,"function":"getAccount","class":"OC\\Accounts\\AccountManager","type":"->"},{"file":"/srv/nextcloud/3rdparty/sabre/dav/lib/DAV/PropFind.php","line":95,"function":"OCA\\DAV\\Connector\\Sabre\\{closure}","class":"OCA\\DAV\\Connector\\Sabre\\FilesPlugin","type":"->","args":["*** sensitive parameters replaced ***"]},{"file":"/srv/nextcloud/apps/dav/lib/Connector/Sabre/FilesPlugin.php","line":358,"function":"handle","class":"Sabre\\DAV\\PropFind","type":"->"},{"file":"/srv/nextcloud/3rdparty/sabre/event/lib/WildcardEmitterTrait.php","line":89,"function":"handleGetProperties","class":"OCA\\DAV\\Connector\\Sabre\\FilesPlugin","type":"->"},{"file":"/srv/nextcloud/3rdparty/sabre/dav/lib/DAV/Server.php","line":1052,"function":"emit","class":"Sabre\\DAV\\Server","type":"->"},{"file":"/srv/nextcloud/3rdparty/sabre/dav/lib/DAV/Server.php","line":984,"function":"getPropertiesByNode","class":"Sabre\\DAV\\Server","type":"->"},{"file":"/srv/nextcloud/3rdparty/sabre/dav/lib/DAV/Server.php","line":1662,"function":"getPropertiesIteratorForPath","class":"Sabre\\DAV\\Server","type":"->"},{"file":"/srv/nextcloud/3rdparty/sabre/dav/lib/DAV/Server.php","line":1647,"function":"writeMultiStatus","class":"Sabre\\DAV\\Server","type":"->"},{"file":"/srv/nextcloud/3rdparty/sabre/dav/lib/DAV/CorePlugin.php","line":346,"function":"generateMultiStatus","class":"Sabre\\DAV\\Server","type":"->"},{"file":"/srv/nextcloud/3rdparty/sabre/event/lib/WildcardEmitterTrait.php","line":89,"function":"httpPropFind","class":"Sabre\\DAV\\CorePlugin","type":"->"},{"file":"/srv/nextcloud/3rdparty/sabre/dav/lib/DAV/Server.php","line":472,"function":"emit","class":"Sabre\\DAV\\Server","type":"->"},{"file":"/srv/nextcloud/apps/dav/lib/Connector/Sabre/Server.php","line":49,"function":"invokeMethod","class":"Sabre\\DAV\\Server","type":"->"},{"file":"/srv/nextcloud/apps/dav/appinfo/v2/publicremote.php","line":139,"function":"start","class":"OCA\\DAV\\Connector\\Sabre\\Server","type":"->"},{"file":"/srv/nextcloud/public.php","line":82,"args":["/srv/nextcloud/apps/dav/appinfo/v2/publicremote.php"],"function":"require_once"}],"File":"/srv/nextcloud/lib/private/User/LazyUser.php","Line":41,"message":"User not found in backend","exception":[],"CustomMessage":"User not found in backend"},"id":"685323d227983"}

Additional info

No response

Reproduce the federated reshare and inspect the logged trace through apps/dav/lib/Connector/Sabre/FilesPlugin.php, lib/private/Accounts/AccountManager.php, and lib/private/User/LazyUser.php, starting at the publicremote.php entry point. Trace why the remote shared file reaches account lookup with a missing user. Done means the reshare can be accessed without the 500 response or “User not found in backend” error.