OAuth2 Proxy has an Authentication Bypass via X-Forwarded-Uri Header Spoofing

{
  "id": "84c04af082ddaec71066894e419f4ee138ce3a02ff44d08f4140ecfae4b69a89",
  "url": "https://osv.dev/vulnerability/CVE-2026-40575",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "OAuth2 Proxy has an Authentication Bypass via X-Forwarded-Uri Header Spoofing",
    "summary": "OAuth2 Proxy is a reverse proxy that provides authentication using OAuth2 providers. Versions 7.5.0 through 7.15.1 may trust a client-supplied `X-Forwarded-Uri` header when `--reverse-proxy` is enabled and `--skip-auth-regex` or `--skip-auth-route` 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. This can result in an unauthenticated remote attacker bypassing authentication and accessing protected routes without a valid session. Impacted users are deployments that run oauth2-proxy with `--reverse-proxy` enabled and configure at least one `--skip-auth-regex` or `--skip-auth-route` rule. This issue is patched in `v7.15.2`. Some workarounds are available for those who cannot upgrade immediately. Strip any client-provided `X-Forwarded-Uri` header at the reverse proxy or load balancer level; explicitly overwrite `X-Forwarded-Uri` with the actual request URI before forwarding requests to OAuth2 Proxy; restrict direct client access to OAuth2 Proxy so it can only be reached through a trusted reverse proxy; and/or remove or narrow `--skip-auth-regex` / `--skip-auth-route` rules where possible. For nginx-based deployments, ensure `X-Forwarded-Uri` is set by nginx and not passed through from the client.",
    "evidence": "osv:CVE-2026-40575",
    "products": [],
    "severity": "critical",
    "structured": {
      "id": "CVE-2026-40575",
      "aliases": [
        "BIT-oauth2-proxy-2026-40575",
        "BIT-oauth2-proxy-2026-76835",
        "CVE-2026-40575",
        "CVE-2026-76835",
        "GHSA-7x63-xv5r-3p2x",
        "GO-2026-5236"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/oauth2-proxy/oauth2-proxy",
              "type": "GIT",
              "events": [
                {
                  "introduced": "01386bf30348f75590df61a3408187696fef6d4b"
                },
                {
                  "fixed": "5961fd99b42c3625b8ef08690d38be5cb37f44b0"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "7.5.0"
                      },
                      {
                        "fixed": "7.15.2"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StringRangeExpression"
                  },
                  {
                    "cpe": "cpe:2.3:a:oauth2_proxy_project:oauth2_proxy:*:*:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "7.5.0"
                      },
                      {
                        "fixed": "7.15.2"
                      }
                    ],
                    "source": "CPE_RANGE"
                  }
                ]
              }
            }
          ],
          "versions": [
            "v7.15.1",
            "v7.15.0",
            "v7.14.3",
            "v7.14.2",
            "v7.14.1",
            "v7.14.0",
            "v7.13.0",
            "v7.12.0",
            "v7.11.0",
            "v7.10.0",
            "v7.9.0",
            "v7.8.2",
            "v7.8.1",
            "v7.8.0",
            "v7.7.1",
            "v7.7.0",
            "v7.6.0",
            "v7.5.1",
            "v7.5.0"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-40575.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:34.431098752Z",
      "provider": "osv",
      "references": [
        "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-40575.json",
        "https://access.redhat.com/security/cve/CVE-2026-40575",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/40xxx/CVE-2026-40575.json",
        "https://github.com/oauth2-proxy/oauth2-proxy/security/advisories/GHSA-7x63-xv5r-3p2x",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-40575",
        "https://bugzilla.redhat.com/show_bug.cgi?id=2460449"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-290"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/40xxx/CVE-2026-40575.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-40575",
        "evidence": "/id"
      },
      {
        "value": "CVE-2026-76835",
        "evidence": "/aliases"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 501982,
  "published_at": "2026-04-21T23:20:30.486+00:00"
}