9router: Mass assignment in PATCH /api/settings allows authenticated authorization downgrade

Summary

The PATCH /api/settings endpoint writes the entire request body to persistent settings without a field whitelist. An authenticated user can set security-critical fields that are not meant to be modifiable here — notably requireLogin. Setting requireLogin: false disables authentication for the whole application, exposing all protected routes (e.g. /api/keys, /api/providers) to unauthenticated access.

Details

Root cause is unfiltered mass assignment (CWE-915):

• src/app/api/settings/route.js (PATCH handler) parses the body and passes it to updateSettings(body), with special handling only for newPassword and oidcClientSecret. All other fields pass through.
• src/lib/db/repos/settingsRepo.js — updateSettings does next = { ...current, ...updates }, so any key in the body overwrites stored settings, including requireLogin, tunnelDashboardAccess, authMode.
• src/dashboardGuard.js — isAuthenticated returns true whenever settings.requireLogin === false, bypassing auth on all protected routes.

This is distinct from CVE-2026-5842 (CWE-285, pre-auth bypass on /api, patched in 0.3.75). This finding requires a valid authenticated session and abuses input handling, not missing authentication.

PoC

Instance on localhost:20128, default password 123456.

1. Authenticate, capture session: POST /api/auth/login body {"password":"123456"} → 200 {"success":true}
2. Mass-assign with the authenticated session: PATCH /api/settings body {"requireLogin":false} → 200, response confirms "requireLogin":false
3. Verify bypass with NO session/credentials: GET /api/keys → 200, returns full API key list unauthenticated
4. Cleanup (authenticated): PATCH /api/settings body {"requireLogin":true} → GET /api/keys returns 401 again

Impact

Post-authentication mass assignment. Any authenticated user (including one using the default password) can disable authentication globally, then read all stored API keys and provider connection data without credentials, and toggle tunnel/dashboard exposure. Escalates to remote full compromise when chained with the default password 123456 on an instance exposed via tunnel (tunnelDashboardAccess defaults to true).

Suggested fix

Whitelist user-configurable fields in the PATCH handler; move security-critical fields (requireLogin, tunnelDashboardAccess, authMode) to a dedicated endpoint requiring re-authentication (current-password re-entry), mirroring the existing DB export/import re-auth flow.