OAuth2 Proxy: Health Check User-Agent Matching Bypasses Authentication in auth_request Mode

{
  "id": "c3f3e7b667d3b05563cc3d3093b43c2c025345c4737767aebeac9cafa1afd105",
  "url": "https://osv.dev/vulnerability/CVE-2026-34457",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "OAuth2 Proxy: Health Check User-Agent Matching Bypasses Authentication in auth_request Mode",
    "summary": "OAuth2 Proxy is a reverse proxy that provides authentication using OAuth2 providers. Versions prior to 7.15.2 contain a configuration-dependent authentication bypass in deployments where OAuth2 Proxy is used with an auth_request-style integration (such as nginx auth_request) and either --ping-user-agent is set or --gcp-healthchecks is enabled. In affected configurations, OAuth2 Proxy treats any request with the configured health check User-Agent value as a successful health check regardless of the requested path, allowing an unauthenticated remote attacker to bypass authentication and access protected upstream resources. Deployments that do not use auth_request-style subrequests or that do not enable --ping-user-agent/--gcp-healthchecks are not affected. This issue is fixed in 7.15.2.",
    "evidence": "osv:CVE-2026-34457",
    "products": [],
    "severity": "critical",
    "structured": {
      "id": "CVE-2026-34457",
      "aliases": [
        "BIT-oauth2-proxy-2026-34457",
        "CVE-2026-34457",
        "GHSA-5hvv-m4w4-gf6v",
        "GO-2026-5147"
      ],
      "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": "0"
                },
                {
                  "fixed": "5961fd99b42c3625b8ef08690d38be5cb37f44b0"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "fixed": "7.15.2"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StringRangeExpression"
                  },
                  {
                    "range": [
                      {
                        "fixed": "5961fd99b42c3625b8ef08690d38be5cb37f44b0"
                      }
                    ],
                    "source": "REFERENCES_TAG",
                    "original_tag": "v7.15.2"
                  },
                  {
                    "cpe": "cpe:2.3:a:oauth2_proxy_project:oauth2_proxy:*:*:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "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",
            "v7.4.0",
            "v7.3.0",
            "v7.2.1",
            "v7.2.0",
            "v7.1.3",
            "v7.1.2",
            "v7.1.1",
            "v7.1.0",
            "v7.0.1",
            "v7.0.0",
            "v6.1.1",
            "v6.1.0",
            "v6.0.0",
            "v5.1.0",
            "v5.0.0",
            "v4.1.0",
            "v4.0.0",
            "v3.2.0",
            "v3.1.0",
            "v3.0.0",
            "v2.2",
            "v2.1",
            "v2.0.1",
            "v2.0",
            "v1.1.1",
            "v1.1",
            "v1.0"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-34457.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:33.612433935Z",
      "provider": "osv",
      "references": [
        "https://github.com/oauth2-proxy/oauth2-proxy/releases/tag/v7.15.2",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/34xxx/CVE-2026-34457.json",
        "https://github.com/oauth2-proxy/oauth2-proxy/security/advisories/GHSA-5hvv-m4w4-gf6v",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-34457"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-290"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/34xxx/CVE-2026-34457.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-34457",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 501050,
  "published_at": "2026-04-14T22:14:38.937+00:00"
}