{"id":"CVE-2026-76835","summary":"OAuth2 Proxy 7.15.2 through 7.15.4 Authentication Bypass via X-Forwarded-Uri Under the Default Trusted Proxy Set","details":"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.","aliases":["BIT-oauth2-proxy-2026-40575","CVE-2026-40575","GHSA-7x63-xv5r-3p2x","GO-2026-5236"],"modified":"2026-08-30T03:30:29.886846978Z","published":"2026-08-24T17:55:39.829Z","database_specific":{"cwe_ids":["CWE-290"],"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/76xxx/CVE-2026-76835.json","cna_assigner":"VulnCheck"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/76xxx/CVE-2026-76835.json"},{"type":"ADVISORY","url":"https://github.com/oauth2-proxy/oauth2-proxy/security/advisories/GHSA-7x63-xv5r-3p2x"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-76835"},{"type":"ADVISORY","url":"https://www.vulncheck.com/advisories/oauth2-proxy-through-authentication-bypass-via-x-forwarded-uri-under-the-default-trusted-proxy-set"},{"type":"REPORT","url":"https://github.com/oauth2-proxy/oauth2-proxy/issues/3506"},{"type":"PACKAGE","url":"https://github.com/oauth2-proxy/oauth2-proxy"},{"type":"ARTICLE","url":"https://github.com/oauth2-proxy/oauth2-proxy/blob/v7.15.4/pkg/apis/middleware/scope.go"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/oauth2-proxy/oauth2-proxy","events":[{"introduced":"5961fd99b42c3625b8ef08690d38be5cb37f44b0"},{"last_affected":"81ff034fe2ff3246e670c694b02e3267d1ae46bc"}],"database_specific":{"extracted_events":[{"introduced":"7.15.2"},{"last_affected":"7.15.4"}],"source":"AFFECTED_FIELD"}}],"versions":["v7.15.4","v7.15.3","v7.15.2"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-76835.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N"}]}