Rate-limit buckets, login lockout and audit-log source IPs hand-parsed the
leftmost X-Forwarded-For token — a client-controlled value — letting an
attacker rotate it to dodge per-IP limits or forge audit trails.
- config: add TRUST_PROXY_HEADERS / TRUSTED_PROXY_HOPS (+ _env_bool/_env_int)
- create_app: wrap in gated Werkzeug ProxyFix (rightmost trusted hops) before
the limiter/handlers so every remote_addr consumer sees the real client
- new app/utils/client_ip.py::get_client_ip() — the single trusted seam
- replace all six leftmost-XFF parsers (rate_limit, audit middleware,
api_key_auth, api_analytics, audit_service, ddns) with get_client_ip()
- deploy: root .env.example ships TRUST_PROXY_HEADERS=true (behind nginx);
backend/.env.example documents it off for dev
- tests: test_trusted_client_ip.py (7) incl. real flask-limiter bucket isolation
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
