{"id":"CVE-2026-81868","aliases":["EUVD-2026-81899","GHSA-5mq7-rwhj-4fh9"],"status":"published","title":"Steeltoe: Header-forwarded client cert lacks proof of private-key possession","description":"Steeltoe is an open source project that provides a collection of libraries that helps users build cloud-native applications. Prior to 4.3.0, Steeltoe.Security.Authorization.Certificate deployments using AddOrgAndSpacePolicies() and UseCertificateAuthorization() trust the public certificate supplied in the X-Client-Cert request header without proving possession of the corresponding private key. Common Cloud Foundry routers do not remove this header from inbound requests. When inbound requests are not restricted to a known trusted proxy source IP, an attacker who obtains the public certificate of an application instance in the target organization or space and can reach the application can spoof X-Client-Cert to bypass the SameOrg and SameSpace policies for the certificate validity period. This issue is fixed in version 4.3.0.","severity":{"version":"3.1","score":6.5,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N","level":"medium","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-11","score":0.0025,"percentile":0.16523,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-288","CWE-295"],"published":"2026-09-17T15:36:23Z","modified":"2026-10-28T02:30:21Z","fixes":[{"ecosystem":"NuGet","package":"Steeltoe.Security.Authorization.Certificate","fixed_in":["4.3.0"],"sources":["ghsa","osv"]}],"affected":[{"source":"ghsa","ecosystem":"NuGet","package":"Steeltoe.Security.Authorization.Certificate","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"last_affected":"4.2.0"},{"fixed":"4.3.0"}]}]},{"source":"osv","ecosystem":"NuGet","package":"Steeltoe.Security.Authorization.Certificate","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"4.3.0"}]}],"versions":["4.0.0","4.0.0-beta1","4.0.0-rc1","4.1.0","4.2.0"]}],"products":[{"vendor":"kiteworks","product":"security-advisories"},{"vendor":"steeltoeoss","product":"security-advisories"}],"references":[{"url":"https://github.com/SteeltoeOSS/security-advisories/security/advisories/GHSA-5mq7-rwhj-4fh9","tags":["x_refsource_CONFIRM","advisory","web"]},{"url":"https://github.com/SteeltoeOSS/Steeltoe/commit/b626ef3d60aaf19c68eeeed5ee81045406c8c6d0","tags":["x_refsource_MISC","fix","web"]},{"url":"https://github.com/SteeltoeOSS/Steeltoe/releases/tag/4.3.0","tags":["x_refsource_MISC","web"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-81868","tags":["advisory"]},{"url":"https://github.com/advisories/GHSA-5mq7-rwhj-4fh9"},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/81xxx/CVE-2026-81868.json","tags":["advisory"]},{"url":"https://github.com/SteeltoeOSS/security-advisories","tags":["package"]}],"sources":{"cve":[{"id":"CVE-2026-81868","title":"Steeltoe: Header-forwarded client cert lacks proof of private-key possession","description":"Steeltoe is an open source project that provides a collection of libraries that helps users build cloud-native applications. Prior to 4.3.0, Steeltoe.Security.Authorization.Certificate deployments using AddOrgAndSpacePolicies() and UseCertificateAuthorization() trust the public certificate supplied in the X-Client-Cert request header without proving possession of the corresponding private key. Common Cloud Foundry routers do not remove this header from inbound requests. When inbound requests are not restricted to a known trusted proxy source IP, an attacker who obtains the public certificate of an application instance in the target organization or space and can reach the application can spoof X-Client-Cert to bypass the SameOrg and SameSpace policies for the certificate validity period. This issue is fixed in version 4.3.0.","status":"published","published":"2026-09-17T15:36:23.149Z","modified":"2026-09-23T18:46:54.265Z","cvss":[{"version":"3.1","score":6.5,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N","level":"medium","assessor":"cna"}],"cwes":["CWE-288","CWE-295"],"updated_at":"2026-11-02T13:36:18.075535Z"}],"euvd":[{"id":"EUVD-2026-81899","description":"Steeltoe is an open source project that provides a collection of libraries that helps users build cloud-native applications. Prior to 4.3.0, Steeltoe.Security.Authorization.Certificate deployments using AddOrgAndSpacePolicies() and UseCertificateAuthorization() trust the public certificate supplied in the X-Client-Cert request header without proving possession of the corresponding private key. Common Cloud Foundry routers do not remove this header from inbound requests. When inbound requests are not restricted to a known trusted proxy source IP, an attacker who obtains the public certificate of an application instance in the target organization or space and can reach the application can spoof X-Client-Cert to bypass the SameOrg and SameSpace policies for the certificate validity period. This issue is fixed in version 4.3.0.","status":"published","published":"2026-09-17T15:36:23Z","modified":"2026-09-23T18:46:54Z","cvss":[{"version":"3.1","score":6.5,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N","level":"medium"}],"updated_at":"2026-11-02T17:28:00.170339Z"}],"ghsa":[{"id":"GHSA-5mq7-rwhj-4fh9","title":"Steeltoe: Header-forwarded client cert lacks proof of private-key possession","description":"### 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.","status":"published","published":"2026-09-17T20:30:58Z","modified":"2026-09-17T20:31:00Z","cvss":[{"version":"3.1","score":6.5,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N","level":"medium"}],"cwes":["CWE-288","CWE-295"],"updated_at":"2026-11-02T14:41:18.357514Z"}],"nvd":[{"id":"CVE-2026-81868","description":"Steeltoe is an open source project that provides a collection of libraries that helps users build cloud-native applications. Prior to 4.3.0, Steeltoe.Security.Authorization.Certificate deployments using AddOrgAndSpacePolicies() and UseCertificateAuthorization() trust the public certificate supplied in the X-Client-Cert request header without proving possession of the corresponding private key. Common Cloud Foundry routers do not remove this header from inbound requests. When inbound requests are not restricted to a known trusted proxy source IP, an attacker who obtains the public certificate of an application instance in the target organization or space and can reach the application can spoof X-Client-Cert to bypass the SameOrg and SameSpace policies for the certificate validity period. This issue is fixed in version 4.3.0.","status":"published","published":"2026-09-17T16:17:47.607Z","modified":"2026-09-30T17:31:44.573Z","cvss":[{"version":"3.1","score":6.5,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N","level":"medium","assessor":"secondary"}],"cwes":["CWE-288","CWE-295"],"updated_at":"2026-11-02T14:12:49.013904Z"}],"osv":[{"id":"CVE-2026-81868","title":"Steeltoe: Header-forwarded client cert lacks proof of private-key possession","description":"Steeltoe is an open source project that provides a collection of libraries that helps users build cloud-native applications. Prior to 4.3.0, Steeltoe.Security.Authorization.Certificate deployments using AddOrgAndSpacePolicies() and UseCertificateAuthorization() trust the public certificate supplied in the X-Client-Cert request header without proving possession of the corresponding private key. Common Cloud Foundry routers do not remove this header from inbound requests. When inbound requests are not restricted to a known trusted proxy source IP, an attacker who obtains the public certificate of an application instance in the target organization or space and can reach the application can spoof X-Client-Cert to bypass the SameOrg and SameSpace policies for the certificate validity period. This issue is fixed in version 4.3.0.","status":"published","published":"2026-09-17T15:36:23.149Z","modified":"2026-10-28T02:30:21.264253349Z","cvss":[{"version":"3.1","score":6.5,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N","level":"medium"}],"cwes":["CWE-288","CWE-295"],"updated_at":"2026-11-02T15:45:18.131258Z"},{"id":"GHSA-5mq7-rwhj-4fh9","title":"Steeltoe: Header-forwarded client cert lacks proof of private-key possession","description":"### 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.","status":"published","published":"2026-09-17T20:30:58Z","modified":"2026-09-17T20:45:06.060192758Z","cvss":[{"version":"3.1","score":6.5,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N","level":"medium"}],"cwes":["CWE-288","CWE-295"],"updated_at":"2026-11-02T15:46:38.553953Z"}]}}