CVE-2026-76835
GetRequestURI in pkg/requests/util/util.go prefers that header over the real request URI whenever CanTrustForwardedHeaders returns true, and isAllowedPath in oauthproxy.go matches the skip_auth_routes and skip_auth_regex allow list against the resulting…
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (0.45%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
Description
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 in pkg/requests/util/util.go prefers that header over the real request URI whenever CanTrustForwardedHeaders returns true, and isAllowedPath in oauthproxy.go matches the skip_auth_routes and skip_auth_regex allow list against the resulting path. CanTrustForwardedHeaders in pkg/apis/middleware/scope.go 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.
- CVSS 4.0
- 9.3 CRITICALCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/M
- EPSS
- 0.45% probability · 39th percentile
- Public exploits
- None in Exploit-DB
- CISA KEV
- Not listed
- Weakness
- CWE-290
- Source
- disclosure@vulncheck.com
EPSS 0.5% since 27 October 2026; no change recorded yet. Points are recorded when the score first appears and whenever it moves by a percentage point or more.
References
- https://github.com/oauth2-proxy/oauth2-proxy
- https://github.com/oauth2-proxy/oauth2-proxy/blob/v7.15.4/pkg/apis/middleware/scope.go
- https://github.com/oauth2-proxy/oauth2-proxy/issues/3506
- https://github.com/oauth2-proxy/oauth2-proxy/security/advisories/GHSA-7x63-xv5r-3p2x
- https://www.vulncheck.com/advisories/oauth2-proxy-through-authentication-bypass-via-x-forwarded-uri-under-the-default-trusted-proxy-set
- https://github.com/oauth2-proxy/oauth2-proxy/issues/3506
Source: NVD record, EPSS from FIRST.org, KEV from CISA, exploits from Exploit-DB. Refreshed daily. Download this record as JSON.