CVE-2026-53519: Nezha Monitoring: Pre-auth path traversal via /dashboard.. prefix confusion leaks jwt_secret_key

fallbackToFrontend in the dashboard’s NoRoute handler treats any URL whose raw string starts with /dashboard as an admin-frontend asset request. The check uses strings.HasPrefix, not a path-segment match, so the input /dashboard../data/config.yaml is accepted; strings.TrimPrefix leaves ../data/config.yaml; and path.Join("admin-dist", "../data/config.yaml") normalizes to data/config.yaml — which os.Stat finds and http.ServeFile returns. No authentication required.

In default deployments (the values shipped in model/config.go and the layout shipped in the project Dockerfile) data/config.yaml contains the HS256 jwt_secret_key used by cmd/dashboard/controller/jwt.go to sign every dashboard session cookie. A unauth attacker reads that secret, forges an admin JWT, and signs in as any user — full dashboard takeover from one GET request.