CVE-2026-40575: Github.com/oauth2 proxy/oauth2 proxy/v7 Authentication Bypass Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-7x63-xv5r-3p2x",
  "modified" : "2026-07-21T13:50:15Z",
  "published" : "2026-04-15T19:21:06Z",
  "aliases" : [ "CVE-2026-40575" ],
  "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",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/oauth2-proxy/oauth2-proxy/v7"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "7.5.0"
      }, {
        "fixed" : "7.15.2"
      } ]
    } ]
  } ],
  "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"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-290" ],
    "severity" : "CRITICAL",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-15T19:21:06Z",
    "nvd_published_at" : "2026-04-22T00:16:27Z"
  }
}