{"affected":[{"database_specific":{"last_known_affected_version_range":"<= 4.2.0","source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/09/GHSA-5mq7-rwhj-4fh9/GHSA-5mq7-rwhj-4fh9.json"},"package":{"ecosystem":"NuGet","name":"Steeltoe.Security.Authorization.Certificate","purl":"pkg:nuget/Steeltoe.Security.Authorization.Certificate"},"ranges":[{"events":[{"introduced":"0"},{"fixed":"4.3.0"}],"type":"ECOSYSTEM"}],"versions":["4.0.0","4.0.0-beta1","4.0.0-rc1","4.1.0","4.2.0"]}],"aliases":["CVE-2026-81868"],"database_specific":{"cwe_ids":["CWE-288","CWE-295"],"github_reviewed":true,"github_reviewed_at":"2026-09-17T20:30:58Z","nvd_published_at":"2026-09-17T16:17:47Z","severity":"MODERATE"},"details":"### Summary\n\nWhen Steeltoe's certificate-based authorization (`UseCertificateAuthorization`) is configured, the default configuration of the middleware relies on the `X-Client-Cert` HTTP header to identify the client certificate, without verifying private-key possession. This header is not stripped by common Cloud Foundry routers (like Gorouter or Envoy) on inbound requests.\n\n### Impact\n\nAn attacker who obtains the public certificate of an application instance in the target organization or space can spoof the `X-Client-Cert` header. This allows the attacker to bypass `SameOrg` and `SameSpace` authorization policies, granting unauthorized access to protected endpoints for the duration of the certificate's validity period.\n\n### Affected configuration\n\n- The application uses `AddOrgAndSpacePolicies()` and `UseCertificateAuthorization()` for inter-service authorization.\n- Inbound requests are not restricted to a known trusted proxy source IP.\n- The application's endpoints are network-accessible to the attacker (e.g., exposed to the internet via a public Cloud Foundry route, or the attacker has access to the internal Cloud Foundry network).\n\n### Mitigations\n\nIf an immediate upgrade to a patched version is not possible:\n\n- Restrict `UseCertificateForwarding` to trusted proxy source IPs using `ForwardedHeadersOptions.KnownProxies` and `KnownNetworks`.\n- Change the forwarding header to `X-Forwarded-Client-Cert` so that Cloud Foundry Gorouter and Envoy header stripping mechanisms apply to inbound untrusted requests.\n- Add a secondary authorization layer (e.g., a shared secret or mutual TLS at the proxy layer) for sensitive endpoints.\n- Ensure the application is not bound to a public route unless explicitly required. Use Cloud Foundry internal routes (e.g., `.apps.internal`) and container-to-container network policies to strictly limit network access to intended internal clients.","id":"GHSA-5mq7-rwhj-4fh9","modified":"2026-09-17T20:45:06.060192758Z","published":"2026-09-17T20:30:58Z","references":[{"type":"WEB","url":"https://github.com/SteeltoeOSS/security-advisories/security/advisories/GHSA-5mq7-rwhj-4fh9"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-81868"},{"type":"WEB","url":"https://github.com/SteeltoeOSS/Steeltoe/commit/b626ef3d60aaf19c68eeeed5ee81045406c8c6d0"},{"type":"WEB","url":"https://github.com/SteeltoeOSS/Steeltoe/releases/tag/4.3.0"},{"type":"PACKAGE","url":"https://github.com/SteeltoeOSS/security-advisories"}],"schema_version":"1.9.0","severity":[{"score":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N","type":"CVSS_V3"}],"summary":"Steeltoe: Header-forwarded client cert lacks proof of private-key possession"}