Unresponsive SFTP external storage blocks access to unrelated files

⚠️ 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

Hi,
I just discovered, that an unresponsive external Storage provider (SFTP) can make nextcloud unusable and you wont get helpful error messages.

Relevant Versions running:

• Nextcloud Hub 9 (30.0.2)
• External storage support -Version 1.22.0

Steps to reproduce

1.I am using Nextcloud Docker installation from dockerhub -> tag latest -> https://hub.docker.com/layers/library/nextcloud/latest/images/sha256-63fb5f32eace75c4770a324c13f9c199f45d5d2cfe10871ba48c820c614c9713?context=explore
2.activate the External storage support (I followed the Bug link from the app and came here)
3. include an external storage (I discovered the problem with an SFTP Provider)
4. everything works fine
5. external storage provider become unresponsive
6. calling the URL apps/files/files -> you get an error like "directory unavailable" - I am not able to find the exact message
7. nextcloud.log is not very helpful to non developers: see attached log

Expected behavior

I would expect in nextcloud hosted files (apart from the external storage in question) still being available.
I would also expect other error handling -> grey out/make red etc. the directory of the external storage

Nextcloud Server version

30

Operating system

Debian/Ubuntu

PHP engine version

PHP 8.2

Web server

Apache (supported)

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": {
        "maintenance": false,
        "maintenance_window_start": 1,
        "htaccess.RewriteBase": "\/",
        "memcache.local": "\\OC\\Memcache\\APCu",
        "apps_paths": [
            {
                "path": "\/var\/www\/html\/apps",
                "url": "\/apps",
                "writable": false
            },
            {
                "path": "\/var\/www\/html\/custom_apps",
                "url": "\/custom_apps",
                "writable": true
            }
        ],
        "instanceid": "***REMOVED SENSITIVE VALUE***",
        "passwordsalt": "***REMOVED SENSITIVE VALUE***",
        "secret": "***REMOVED SENSITIVE VALUE***",
        "trusted_domains": [
            "REDACTED"
        ],
        "datadirectory": "***REMOVED SENSITIVE VALUE***",
        "dbtype": "mysql",
        "version": "30.0.2.2",
        "overwrite.cli.url": "REDACTED",
        "dbname": "***REMOVED SENSITIVE VALUE***",
        "dbhost": "***REMOVED SENSITIVE VALUE***",
        "dbport": "",
        "dbtableprefix": "oc_",
        "mysql.utf8mb4": true,
        "dbuser": "***REMOVED SENSITIVE VALUE***",
        "dbpassword": "***REMOVED SENSITIVE VALUE***",
        "installed": true,
        "overwriteprotocol": "https",
        "trusted_proxies": "***REMOVED SENSITIVE VALUE***",
        "default_phone_region": "DE",
        "mail_smtpmode": "smtp",
        "mail_smtpsecure": "tls",
        "mail_sendmailmode": "smtp",
        "mail_smtpauth": 1,
        "mail_smtpauthtype": "PLAIN",
        "mail_smtphost": "***REMOVED SENSITIVE VALUE***",
        "mail_domain": "***REMOVED SENSITIVE VALUE***",
        "mail_from_address": "***REMOVED SENSITIVE VALUE***",
        "mail_smtpport": "587",
        "mail_smtpname": "***REMOVED SENSITIVE VALUE***",
        "mail_smtppassword": "***REMOVED SENSITIVE VALUE***",
        "loglevel": 2,
        "theme": "",
        "trashbin_retention_obligation": "31,60",
        "memcache.distributed": "\\OC\\Memcache\\Redis",
        "memcache.locking": "\\OC\\Memcache\\Redis",
        "redis": {
            "host": "***REMOVED SENSITIVE VALUE***",
            "password": "***REMOVED SENSITIVE VALUE***",
            "port": 6379
        }
    }
}

List of activated Apps

Enabled:
  - activity: 3.0.0
  - app_api: 4.0.0
  - bruteforcesettings: 3.0.0
  - calendar: 5.0.5
  - circles: 30.0.0
  - cloud_federation_api: 1.13.0
  - comments: 1.20.1
  - contacts: 6.1.1
  - dashboard: 7.10.0
  - dav: 1.31.1
  - end_to_end_encryption: 1.16.1
  - 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
  - logreader: 3.0.0
  - lookup_server_connector: 1.18.0
  - nextcloud_announcements: 2.0.0
  - notifications: 3.0.0
  - oauth2: 1.18.1
  - password_policy: 2.0.0
  - photos: 3.0.2
  - previewgenerator: 5.7.0
  - privacy: 2.0.0
  - provisioning_api: 1.20.0
  - recommendations: 3.0.0
  - related_resources: 1.5.0
  - serverinfo: 2.0.0
  - settings: 1.13.0
  - sharebymail: 1.20.0
  - systemtags: 1.20.0
  - tasks: 0.16.1
  - text: 4.1.0
  - theming: 2.5.0
  - twofactor_backupcodes: 1.19.0
  - updatenotification: 1.20.0
  - user_status: 1.10.0
  - viewer: 3.0.0
  - weather_status: 1.10.0
  - webhook_listeners: 1.1.0-dev
  - workflowengine: 2.12.0
Disabled:
  - admin_audit: 1.20.0
  - contactsinteraction: 1.11.0 (installed 1.6.0)
  - encryption: 2.18.0
  - firstrunwizard: 3.0.0 (installed 2.14.0)
  - support: 2.0.0 (installed 1.10.0)
  - survey_client: 2.0.0 (installed 1.15.0)
  - suspicious_login: 8.0.0
  - twofactor_nextcloud_notification: 4.0.0
  - twofactor_totp: 12.0.0-dev
  - user_ldap: 1.21.0

Nextcloud Signing status

No errors have been found.

Nextcloud Logs

{"reqId":"REDACTED","level":3,"time":"2024-11-24T13:24:47+00:00","remoteAddr":"REDACTED","user":"REDACTED","app":"index","method":"POST","url":"/apps/files_external/globalstorages","message":"base and exponent overflow in file '/var/www/html/3rdparty/phpseclib/phpseclib/phpseclib/Math/BigInteger.php' line 3040","userAgent":"Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:132.0) Gecko/20100101 Firefox/132.0","version":"30.0.2.2","exception":{"Exception":"Exception","Message":"base and exponent overflow in file '/var/www/html/3rdparty/phpseclib/phpseclib/phpseclib/Math/BigInteger.php' line 3040","Code":0,"Trace":[{"file":"/var/www/html/lib/private/AppFramework/App.php","line":161,"function":"dispatch","class":"OC\\AppFramework\\Http\\Dispatcher","type":"->","args":[{"__class__":"OCA\\Files_External\\Controller\\GlobalStoragesController"},"create"]},{"file":"/var/www/html/lib/private/Route/Router.php","line":302,"function":"main","class":"OC\\AppFramework\\App","type":"::","args":["OCA\\Files_External\\Controller\\GlobalStoragesController","create",{"__class__":"OC\\AppFramework\\DependencyInjection\\DIContainer"},{"_route":"files_external.global_storages.create"}]},{"file":"/var/www/html/lib/base.php","line":1001,"function":"match","class":"OC\\Route\\Router","type":"->","args":["/apps/files_external/globalstorages"]},{"file":"/var/www/html/index.php","line":24,"function":"handleRequest","class":"OC","type":"::","args":[]}],"File":"/var/www/html/lib/private/AppFramework/Http/Dispatcher.php","Line":146,"Previous":{"Exception":"ValueError","Message":"base and exponent overflow","Code":0,"Trace":[{"file":"/var/www/html/3rdparty/phpseclib/phpseclib/phpseclib/Math/BigInteger.php","line":3040,"function":"gmp_pow","args":[{"__class__":"GMP"},256]},{"file":"/var/www/html/3rdparty/phpseclib/phpseclib/phpseclib/Net/SSH2.php","line":1846,"function":"bitwise_leftShift","class":"phpseclib\\Math\\BigInteger","type":"->","args":[256]},{"file":"/var/www/html/3rdparty/phpseclib/phpseclib/phpseclib/Net/SSH2.php","line":1435,"function":"_key_exchange","class":"phpseclib\\Net\\SSH2","type":"->","args":[]},{"file":"/var/www/html/3rdparty/phpseclib/phpseclib/phpseclib/Net/SSH2.php","line":5217,"function":"_connect","class":"phpseclib\\Net\\SSH2","type":"->","args":[]},{"file":"/var/www/html/apps/files_external/lib/Lib/Storage/SFTP.php","line":110,"function":"getServerPublicHostKey","class":"phpseclib\\Net\\SSH2","type":"->","args":[]},{"file":"/var/www/html/apps/files_external/lib/Lib/Storage/SFTP.php","line":145,"function":"getConnection","class":"OCA\\Files_External\\Lib\\Storage\\SFTP","type":"->","args":[]},{"file":"/var/www/html/apps/files_external/lib/MountConfig.php","line":98,"function":"test","class":"OCA\\Files_External\\Lib\\Storage\\SFTP","type":"->","args":["*** sensitive parameters replaced ***","*** sensitive parameters replaced ***"]},{"file":"/var/www/html/apps/files_external/lib/Controller/StoragesController.php","line":224,"function":"getBackendStatus","class":"OCA\\Files_External\\MountConfig","type":"::","args":["*** sensitive parameters replaced ***"]},{"file":"/var/www/html/apps/files_external/lib/Controller/GlobalStoragesController.php","line":115,"function":"updateStorageStatus","class":"OCA\\Files_External\\Controller\\StoragesController","type":"->","args":["*** sensitive parameters replaced ***"]},{"file":"/var/www/html/lib/private/AppFramework/Http/Dispatcher.php","line":208,"function":"create","class":"OCA\\Files_External\\Controller\\GlobalStoragesController","type":"->","args":["*** sensitive parameters replaced ***"]},{"file":"/var/www/html/lib/private/AppFramework/Http/Dispatcher.php","line":114,"function":"executeController","class":"OC\\AppFramework\\Http\\Dispatcher","type":"->","args":[{"__class__":"OCA\\Files_External\\Controller\\GlobalStoragesController"},"create"]},{"file":"/var/www/html/lib/private/AppFramework/App.php","line":161,"function":"dispatch","class":"OC\\AppFramework\\Http\\Dispatcher","type":"->","args":[{"__class__":"OCA\\Files_External\\Controller\\GlobalStoragesController"},"create"]},{"file":"/var/www/html/lib/private/Route/Router.php","line":302,"function":"main","class":"OC\\AppFramework\\App","type":"::","args":["OCA\\Files_External\\Controller\\GlobalStoragesController","create",{"__class__":"OC\\AppFramework\\DependencyInjection\\DIContainer"},{"_route":"files_external.global_storages.create"}]},{"file":"/var/www/html/lib/base.php","line":1001,"function":"match","class":"OC\\Route\\Router","type":"->","args":["/apps/files_external/globalstorages"]},{"file":"/var/www/html/index.php","line":24,"function":"handleRequest","class":"OC","type":"::","args":[]}],"File":"/var/www/html/3rdparty/phpseclib/phpseclib/phpseclib/Math/BigInteger.php","Line":3040},"message":"base and exponent overflow in file '/var/www/html/3rdparty/phpseclib/phpseclib/phpseclib/Math/BigInteger.php' line 3040","exception":{},"CustomMessage":"base and exponent overflow in file '/var/www/html/3rdparty/phpseclib/phpseclib/phpseclib/Math/BigInteger.php' line 3040"}}

Additional info

No response

Start with the stack trace through apps/files_external/lib/Lib/Storage/SFTP.php, MountConfig.php, and the storage controllers, then inspect the phpseclib SSH connection path. Reproduce an unresponsive SFTP provider while accessing unrelated files. Done means unrelated hosted files remain available and the unavailable external directory receives a clear error state or message.