Vaultwarden breaks when Traefik error catcher includes status 400

[Nicolas-Delahaie]

Prerequisites

• I have searched the existing Closed AND Open Issues AND Discussions
• I have searched and read the documentation

Vaultwarden Support String

Your environment (Generated via diagnostics page)

• Vaultwarden version: v1.34.3
• Web-vault version: v2025.7.0
• OS/Arch: linux/x86_64
• Running within a container: true (Base: Debian)
• Database type: SQLite
• Database version: 3.50.2
• Uses config.json: false
• Uses a reverse proxy: true
• IP Header check: true (X-Real-IP)
• Internet access: true
• Internet access via a proxy: false
• DNS Check: true
• Browser/Server Time Check: true
• Server/NTP Time Check: true
• Domain Configuration Check: true
• HTTPS Check: true
• Websocket Check: true
• HTTP Response Checks: false

Config & Details (Generated via diagnostics page)

Show Config & Details

Failed HTTP Checks:

API calls:
Header: 'referrer-policy' does not contain 'same-origin'
2FA Connector calls:
Header: 'referrer-policy' does not contain 'same-origin'

Config:

{
  "_duo_akey": null,
  "_enable_duo": true,
  "_enable_email_2fa": false,
  "_enable_smtp": true,
  "_enable_yubico": true,
  "_icon_service_csp": "",
  "_icon_service_url": "",
  "_ip_header_enabled": true,
  "_max_note_size": 10000,
  "_smtp_img_src": "***:",
  "admin_ratelimit_max_burst": 3,
  "admin_ratelimit_seconds": 300,
  "admin_session_lifetime": 10,
  "admin_token": "***",
  "allowed_connect_src": "",
  "allowed_iframe_ancestors": "",
  "attachments_folder": "data/attachments",
  "auth_request_purge_schedule": "30 * * * * *",
  "authenticator_disable_time_drift": false,
  "data_folder": "data",
  "database_conn_init": "",
  "database_max_conns": 10,
  "database_timeout": 30,
  "database_url": "***************",
  "db_connection_retries": 15,
  "disable_2fa_remember": true,
  "disable_admin_token": false,
  "disable_icon_download": false,
  "domain": "*****://**********************",
  "domain_origin": "*****://**********************",
  "domain_path": "",
  "domain_set": true,
  "duo_context_purge_schedule": "30 * * * * *",
  "duo_host": null,
  "duo_ikey": null,
  "duo_skey": null,
  "duo_use_iframe": false,
  "email_2fa_auto_fallback": false,
  "email_2fa_enforce_on_verified_invite": false,
  "email_attempts_limit": 3,
  "email_change_allowed": true,
  "email_expiration_time": 600,
  "email_token_size": 6,
  "emergency_access_allowed": true,
  "emergency_notification_reminder_schedule": "0 3 * * * *",
  "emergency_request_timeout_schedule": "0 7 * * * *",
  "enable_db_wal": true,
  "enable_websocket": true,
  "enforce_single_org_with_reset_pw_policy": false,
  "event_cleanup_schedule": "0 10 0 * * *",
  "events_days_retain": null,
  "experimental_client_feature_flags": "",
  "extended_logging": true,
  "helo_name": null,
  "hibp_api_key": null,
  "http_request_block_non_global_ips": true,
  "http_request_block_regex": null,
  "icon_blacklist_non_global_ips": true,
  "icon_blacklist_regex": null,
  "icon_cache_folder": "data/icon_cache",
  "icon_cache_negttl": 259200,
  "icon_cache_ttl": 2592000,
  "icon_download_timeout": 10,
  "icon_redirect_code": 302,
  "icon_service": "internal",
  "incomplete_2fa_schedule": "30 * * * * *",
  "incomplete_2fa_time_limit": 3,
  "increase_note_size_limit": false,
  "invitation_expiration_hours": 120,
  "invitation_org_name": "Vaultwarden",
  "invitations_allowed": false,
  "ip_header": "X-Real-IP",
  "job_poll_interval_ms": 30000,
  "log_file": null,
  "log_level": "trace",
  "log_timestamp_format": "%Y-%m-%d %H:%M:%S.%3f",
  "login_ratelimit_max_burst": 10,
  "login_ratelimit_seconds": 60,
  "org_attachment_limit": null,
  "org_creation_users": "",
  "org_events_enabled": false,
  "org_groups_enabled": false,
  "password_hints_allowed": false,
  "password_iterations": 600000,
  "push_enabled": false,
  "push_identity_uri": "https://identity.bitwarden.com",
  "push_installation_id": "***",
  "push_installation_key": "***",
  "push_relay_uri": "https://push.bitwarden.com",
  "reload_templates": false,
  "require_device_email": false,
  "rsa_key_filename": "data/rsa_key",
  "send_purge_schedule": "0 5 * * * *",
  "sendmail_command": null,
  "sends_allowed": true,
  "sends_folder": "data/sends",
  "show_password_hint": false,
  "signups_allowed": false,
  "signups_domains_whitelist": "",
  "signups_verify": false,
  "signups_verify_resend_limit": 6,
  "signups_verify_resend_time": 3600,
  "smtp_accept_invalid_certs": false,
  "smtp_accept_invalid_hostnames": false,
  "smtp_auth_mechanism": null,
  "smtp_debug": false,
  "smtp_embed_images": true,
  "smtp_explicit_tls": null,
  "smtp_from": "",
  "smtp_from_name": "Vaultwarden",
  "smtp_host": null,
  "smtp_password": null,
  "smtp_port": 587,
  "smtp_security": "starttls",
  "smtp_ssl": null,
  "smtp_timeout": 15,
  "smtp_username": null,
  "templates_folder": "data/templates",
  "tmp_folder": "data/tmp",
  "trash_auto_delete_days": null,
  "trash_purge_schedule": "0 5 0 * * *",
  "use_sendmail": false,
  "use_syslog": false,
  "user_attachment_limit": null,
  "user_send_limit": null,
  "web_vault_enabled": true,
  "web_vault_folder": "web-vault/",
  "yubico_client_id": null,
  "yubico_secret_key": null,
  "yubico_server": null
}

Vaultwarden Build Version

1.34.3

Deployment method

Official Container Image

Custom deployment method

No response

Reverse Proxy

Traefik 3.5.2

Host/Server Operating System

Linux

Operating System Version

No response

Clients

Web Vault

Client Version

Every clients, whichever version

Steps To Reproduce

1. Run Vaultwarden behind Traefik.
2. Add an error catcher middleware for HTTP errors:

http:
  middlewares:
    errp-redirect:
      errors:
        status:
          - "400-599"
        service: error-service
        query: "/{status}.html"

  vw:
    labels:
      traefik.http.routers.vw.middlewares: errp-redirect@file

3. Try to log in to Vaultwarden.

Expected Result

Vaultwarden login should succeed, same as when the middleware is set to 401-599.

Actual Result

Without 400 (401-599) : login works fine.
With 400 (400-599) : Vaultwarden breaks at login, authentication fails (see image)

Logs

Screenshots or Videos

Additional Context

No response

[BlackDex]

Yes that isn't an issue of Vaultwarden but your config. Remove those error redirects as these error codes are needed for the clients to work correctly.

[BlackDex]

To be clear, all error codes, not only 400.

[Nicolas-Delahaie]

Thanks for your reply.
I’ve already resolved my issue, but I opened this PR mainly to help others, since the current “undefined …” error message could be confusing.

[BlackDex]

This project doesn't develop or maintain the clients, and thus nothing we can do.

If your intention was to let others know, then you should have created a discussion as mentioned in the template.