Vulnerability · Published Aug 24, 2026 · Assigned by VulnCheck
CVE-2026-76835OAuth2 Proxy 7.15.2 through 7.15.4 Authentication Bypass via X-Forwarded-Uri Under the Default Trusted Proxy Set
Critical 9.1
In plain English
A critical-severity authentication bypass by spoofing in oauth2-proxy from oauth2-proxy. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 39% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Go | github.com/oauth2-proxy/oauth2-proxy | no fix listed | GO-2026-5236 |
| Go | github.com/oauth2-proxy/oauth2-proxy/v7 | 7.15.2 | GHSA-7x63-xv5r-3p2x |
| Go | github.com/oauth2-proxy/oauth2-proxy/v7 | 7.15.2 | GO-2026-5236 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| oauth2-proxy | oauth2-proxy | 7.15.2 – through 7.15.4 |
Weakness: CWE-290 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
References
- https://github.com/oauth2-proxy/oauth2-proxy product
- https://github.com/oauth2-proxy/oauth2-proxy/issues/3506 issue-tracking
- https://github.com/oauth2-proxy/oauth2-proxy/blob/v7.15.4/pkg/apis/middleware/scope.go technical-description
- GitHub Security Advisory (GHSA-7x63-xv5r-3p2x) vendor-advisory
- VulnCheck Advisory: OAuth2 Proxy 7.15.2 through 7.15.4 Authentication Bypass via X-Forwarded-Uri Under the Default Trusted Proxy Set third-party-advisory