Open WebUI: Path traversal / SSRF in terminal server proxy via encoded path traversal

Summary

The terminal-server reverse proxy in backend/open_webui/routers/terminals.py does not fully confine the user-controlled path segment before forwarding it to an admin-configured terminal server. An authenticated user who has been granted access to a terminal server can craft path values containing encoded ../ traversal sequences that escape the intended path (or policy) scope on that server, reaching unintended endpoints and files on the terminal-server host. Where the terminal server fans requests out to internal services, this also gives SSRF-style reach into those services.

This is a separate code path from the /api/v1/retrieval/process/web SSRF (GHSA-c6xv-rcvw-v685), with its own input. Two distinct vectors are consolidated here:

1. Raw path forwarding / single-encoded traversal (original report).
2. A bypass of the subsequently-added _sanitize_proxy_path mitigation using double-encoded dots (%252e%252e).

The attacker-controlled input is the request path, supplied by the non-admin user, not anything an administrator configures, so this is not an admin-trust / Rule-9 situation.

Affected code

The proxy route forwards an arbitrary trailing path to the configured terminal server:

# routers/terminals.py
@router.api_route('/{server_id}/{path:path}', methods=PROXY_METHODS)
async def proxy_terminal(server_id, path, request, user=Depends(get_verified_user)):
    ...
    safe_path = _sanitize_proxy_path(path)
    if safe_path is None:
        return JSONResponse({'error': 'Invalid path'}, status_code=400)
    target_url = f'{base_url}/{safe_path}'
    policy_id = connection.get('policy_id')
    if policy_id:
        target_url = f'{base_url}/p/{policy_id}/{safe_path}'

Access requires has_connection_access(user, connection, ...), i.e. a non-admin user the administrator has granted to that terminal server.