ClientIP used r.RemoteAddr and ignored X-Forwarded-For. That was right
about not trusting the header from an untrusted peer, but it is only half
the design: behind a proxy every request arrives from the proxy, so the
limiter key in handlers.go was "<proxy-ip>|<username>" for every client on
the internet. One attacker locked out a username for everyone, an attacker
rotating usernames never hit a limit, and sessions.ip recorded the proxy
so the device list was useless.
- VELLUM_TRUSTED_PROXIES is a CIDR list. X-Forwarded-For is honoured only
when RemoteAddr is inside it, and the chain is walked right-to-left so
the first address that is not itself a trusted proxy wins. Everything to
its left was appended by a client we do not control, so a spoofed
leftmost entry is discarded.
- VELLUM_PUBLIC_URL is the external origin. CookieSecure now defaults to
true when it is https://, so a TLS deployment that forgets
VELLUM_COOKIE_SECURE no longer ships a plaintext session cookie.
- A malformed CIDR fails the boot rather than being skipped: silently
dropping a proxy network widens the trust boundary, which is the exact
failure this setting exists to prevent.
ClientIP became a method on Authenticator so it can see the trusted set,
which is why handlers.go and main.go changed as well.
Verified red-green: neutering the trusted-peer path fails five ClientIP
tests, including the spoofed-leftmost case.
Known gap, pre-existing and not fixed here: this limiter still covers only
/api/v1/auth/login. Jellyfin AuthenticateByName and Subsonic auth call
auth.Authenticate with no limiting, so the same brute force is available
through those two surfaces.
