Nginx UI: Bundled reverse proxy can bypass IP allowlists and enable shared login lockout

Summary

In Nginx UI versions 2.2.0 through 2.5.x, the official bundled reverse-proxy topology did not preserve the external client identity used by Gin. The backend treated the local proxy peer as the client because no trusted proxy was configured, while the proxy supplied the actual address in forwarding headers.

Impact

This has two distinct effects in bundled-proxy deployments:

• IP allowlist enforcement: management API requests forwarded by the bundled proxy were identified as loopback and could pass the loopback exception even when the external source was not in the configured allowlist. Protected management operations still required valid credentials; this did not grant unauthenticated administrator access.
• Login availability: failed login attempts from different external sources were attributed to one loopback address. An unauthenticated attacker could therefore trigger the shared temporary login-ban threshold and deny password or OTP login to other users behind the proxy until the ban expired. Existing authenticated sessions were not invalidated.

Remediation

Upgrade to Nginx UI 2.6.0 or later. The fix explicitly trusts only the intended bundled proxy, validates configured trusted proxies, uses the resolved client address consistently, and fails closed when an IP allowlist is enabled but the client address is invalid.

Fix commit: https://github.com/0xJacky/nginx-ui/commit/e30e331303fc21cf077a2bea724bd79e66892eaf