{"id":"GHSA-7x63-xv5r-3p2x","summary":"OAuth2 Proxy has an Authentication Bypass via X-Forwarded-Uri Header Spoofing","details":"### Impact\n\nA configuration-dependent authentication bypass exists in OAuth2 Proxy.\n\nDeployments are affected when all of the following are true:\n\n* OAuth2 Proxy is configured with `--reverse-proxy`\n* and at least one rule is defined with `--skip_auth_routes` or the legacy `--skip-auth-regex`\n\nOAuth2 Proxy may trust a client-supplied `X-Forwarded-Uri` header when `--reverse-proxy` is enabled and `--skip-auth-route` or `--skip-auth-regex` is configured. An attacker can spoof this header so OAuth2 Proxy evaluates authentication and skip-auth rules against a different path than the one actually sent to the upstream application.\n\nThis can result in an unauthenticated remote attacker bypassing authentication and accessing protected routes without a valid session.\n\n\n### Patches\nThis issue is addressed as part of the newly introduced `--trusted-proxy-ip` flag in `v7.15.2`. If you leave it unset, OAuth2 Proxy will **continue to trust ALL** source IPs (0.0.0.0/0) for backwards compatibility, which means a client may still be able to spoof forwarded headers. Therefore after upgrading we urge you to use the new `--trusted-proxy-ip` flag to set the IPs or CIDR ranges of the reverse proxies that are allowed to send `X-Forwarded-*` headers and furthermore implement the mitigation steps outlined below to properly configure your load balancer infrastructure.\n\n### Mitigation\n\n- Strip any client-provided `X-Forwarded-Uri` header at the reverse proxy or load balancer level\n- Explicitly overwrite `X-Forwarded-Uri` with the actual request URI before forwarding requests to OAuth2 Proxy\n\n  Example nginx mitigation for the auth subrequest:\n  ```\n    location /internal-auth/ {\n      internal; # Ensure external users can't access this path\n  \n      # Make sure the OAuth2 Proxy knows where the original request came from.\n      proxy_set_header Host       $host;\n      proxy_set_header X-Real-IP  $remote_addr;\n      # set the value to the actual $request_uri and therefore strip any user provided X-Forwarded-Uri\n      proxy_set_header X-Forwarded-Uri $request_uri;\n  \n      proxy_pass http://oauth2-proxy:4180/;\n    }\n  ```\n- Restrict direct client access to OAuth2 Proxy so it can only be reached through a trusted reverse proxy\n- Remove or narrow `--skip-auth-route` / `--skip-auth-regex` rules where possible","aliases":["BIT-oauth2-proxy-2026-40575","BIT-oauth2-proxy-2026-76835","CVE-2026-40575","CVE-2026-76835","GO-2026-5236"],"modified":"2026-09-25T14:25:56.584542414Z","published":"2026-04-15T19:21:06Z","database_specific":{"nvd_published_at":"2026-04-22T00:16:27Z","cwe_ids":["CWE-290"],"severity":"CRITICAL","github_reviewed":true,"github_reviewed_at":"2026-04-15T19:21:06Z"},"references":[{"type":"WEB","url":"https://github.com/oauth2-proxy/oauth2-proxy/security/advisories/GHSA-7x63-xv5r-3p2x"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-40575"},{"type":"WEB","url":"https://access.redhat.com/security/cve/CVE-2026-40575"},{"type":"WEB","url":"https://bugzilla.redhat.com/show_bug.cgi?id=2460449"},{"type":"PACKAGE","url":"https://github.com/oauth2-proxy/oauth2-proxy"},{"type":"WEB","url":"https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-40575.json"}],"affected":[{"package":{"name":"github.com/oauth2-proxy/oauth2-proxy/v7","ecosystem":"Go","purl":"pkg:golang/github.com/oauth2-proxy/oauth2-proxy/v7"},"ranges":[{"type":"SEMVER","events":[{"introduced":"7.5.0"},{"fixed":"7.15.2"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/04/GHSA-7x63-xv5r-3p2x/GHSA-7x63-xv5r-3p2x.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N"}]}