CVE-2026-34457

CVE-2017-1000069 describes a CSRF vulnerability in oauth2_proxy version 2.1 that can occur during the authentication flow.

OAuth2 Proxy honours a client-supplied X-Forwarded-Uri header when deciding whether a request may skip authentication, because the guard added for CVE-2026-40575 is inert in the default reverse-proxy configuration. GetRequestURI prefers that header over the real request URI whenever CanTrustForwardedHeaders returns true, and isAllowedPath matches the skip_auth_routes and skip_auth_regex allow list against the resulting path. CanTrustForwardedHeaders grants that trust when the caller's address is in the trusted proxy set, and buildTrustedProxyNetSet falls back to defaultTrustedProxyIPs, which is 0.0.0.0/0 and ::/0, whenever reverse proxy mode is enabled without trusted_proxy_ip configured. Every client is therefore treated as a trusted proxy. An unauthenticated attacker can request a protected upstream path while setting X-Forwarded-Uri to a value matching an allow-listed route, so the skip-auth decision is made against the spoofed value while the upstream receives the protected path unchanged.

OAuth2 Proxy versions 7.5.0 through 7.15.1 may trust a client-supplied `X-Forwarded-Uri` header when `--reverse-proxy` is enabled and `--skip-auth-regex` or `--skip-auth-route` is configured. An attacker can spoof this header to bypass authentication and access protected routes without a valid session.

A regression introduced in OAuth2 Proxy 7.11.0 prevents clearing the session cookie when rendering the sign-in page. In deployments relying on the sign-in page as part of the logout flow, a user may be shown the sign-in page while the existing session cookie remains valid, meaning the browser session is not actually logged out. On shared workstations, a subsequent user could continue the previous user's authenticated session. This is fixed in version 7.15.2.