{"id":"CVE-2026-76835","title":"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","summary":"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/r…","severity":"critical","cvss":9.1,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N","cwe":["CWE-290"],"vendor":"oauth2-proxy","product":"oauth2-proxy","affected":["oauth2-proxy >= 7.15.2 <= 7.15.4"],"patched":["hardened_images"],"published":"2026-08-24","updated":"2026-10-13","sourceUpdated":"2026-10-13T09:10:00.323","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-76835","references":[{"url":"https://github.com/oauth2-proxy/oauth2-proxy","label":"disclosure@vulncheck.com"},{"url":"https://github.com/oauth2-proxy/oauth2-proxy/blob/v7.15.4/pkg/apis/middleware/scope.go","label":"disclosure@vulncheck.com"},{"url":"https://github.com/oauth2-proxy/oauth2-proxy/issues/3506","label":"disclosure@vulncheck.com"},{"url":"https://github.com/oauth2-proxy/oauth2-proxy/security/advisories/GHSA-7x63-xv5r-3p2x","label":"disclosure@vulncheck.com"},{"url":"https://www.vulncheck.com/advisories/oauth2-proxy-through-authentication-bypass-via-x-forwarded-uri-under-the-default-trusted-proxy-set","label":"disclosure@vulncheck.com"},{"url":"https://github.com/oauth2-proxy/oauth2-proxy/issues/3506","label":"134c704f-9b21-4f2e-91b3-4a467353bcc0"},{"url":"https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-76835.json"},{"url":"https://access.redhat.com/security/cve/CVE-2026-76835"},{"url":"https://bugzilla.redhat.com/show_bug.cgi?id=2522418"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-76835"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-76835"},{"url":"https://access.redhat.com/errata/RHSA-2026:74536"}],"tags":["nvd","cve.org","exploit-available","csaf","vex","red-hat"],"epss":0.00453,"epssPercentile":0.39157,"exploitAvailable":true,"ssvc":{"exploitation":"poc","automatable":"yes","technicalImpact":"total","timestamp":"2026-08-24T20:00:05.680574Z"},"ingestedAt":"2026-09-24T20:51:40.224Z","slug":"CVE-2026-76835","body":"## Overview\n\nOAuth2 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.\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.\n\n## Vendor advisories\n\n- **Red Hat VEX** · Important · affected: Red Hat OpenShift Dev Spaces · no fix planned: Red Hat OpenShift Dev Spaces · updated 2026-10-02 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-76835.json)\n- **RHSA-2026:74536** · Red Hat · fixed in: Red Hat Hardened Images · released 2026-10-01 · [advisory](https://access.redhat.com/errata/RHSA-2026:74536)","depth":"abyssal","depthScore":62,"depthScoreParts":{"impact":50.1,"likelihood":0.1,"exploitation":12,"ransomware":0},"changes":[{"seq":218155,"id":"CVE-2026-76835","ts":1791478455158,"field":"exploit_available","old":"false","new":"true"}]}