GHSA-pqg7-v6wh-3pfp: TsDProxy: X-Forwarded-For header injection allows IP spoofing in proxied requests to backend services

Description The HTTP reverse proxy handler in tsdproxy does not strip the X-Forwarded-For (or X-Real-IP) header from incoming requests before calling r.SetXForwarded(). This allows an authenticated Tailscale user to inject arbitrary X-Forwarded-For values that are forwarded verbatim to backend services. // internal/proxymanager/port.go -- Rewrite function Rewrite: func(r *httputil.ProxyRequest) { r.SetURL(pconfig.GetFirstTarget()) r.Out.Host = r.In.Host // Strips tsdproxy identity headers (correct) r.Out.Header.Del(consts.HeaderID) r.Out.Header.Del(consts.HeaderRemoteUser) r.Out.Header.Del(consts.HeaderXForwardedUser) // ... other identity headers deleted ... // X-Forwarded-For is NOT deleted before SetXForwarded! // X-Real-IP is NOT deleted at all! r.SetXForwarded() // APPENDS client IP to attacker-controlled XFF list }, Per Go's httputil.ProxyRequest.SetXForwarded() documentation: If the inbound request has an existing X-Forwarded-For header, SetXForwarded appends the inbound request's remote address to the list. Result when attacker sends X-Forwarded-For: 127.0.0.1: - Backend receives: X-Forwarded-For: 127.0.0.1, <real-tailscale-client-ip> - If backend reads first element as "original client", attacker appears as 127.0.0.1 X-Real-IP is not handled at all -- if the attacker sets X-Real-IP: 127.0.0.1, it is forwarded to the backend verbatim without any overriding or stripping. Many backend applications trust the first element of X-Forwarded-For (or X-Real-IP) for: - IP-based access control (admin panels restricted to 127.0.0.1) - Rate limiting tied to source IP - Audit logging - Geo-blocking or network-segment restrictions This is particularly impactful in tsdproxy's intended use case where the backend service is only accessible through tsdproxy -- making the proxy's header handling the sole enforcement point. CVSS CVSS v3.1: AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:H/A:N = 7.7 Severity High Affected Code / Files - internal/proxymanager/port.go -- newPortProxy Rew