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Steeltoe is an open-source project providing libraries for building cloud-native applications. Prior to version 4.3.0, deployments using `Steeltoe.Security.Authorization.Certificate` with `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, such as Gorouter or Envoy, do not strip 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 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. The vulnerability is classified as CWE-288 (Authentication Bypass Using an Alternate Path or Channel) and CWE-295 (Improper Certificate Validation). The CVSS 3.1 base score is 6.5, rated Medium, with the vector CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N. The issue is fixed in version 4.3.0.
DailyCVE Form:
Platform: Steeltoe
Version: < 4.3.0
Vulnerability: Auth bypass
Severity: Medium (6.5)
date: 2026-09-17
Prediction: 2026-09-09
What Undercode Say:
Check installed Steeltoe.Security.Authorization.Certificate version dotnet list package | grep Steeltoe.Security.Authorization.Certificate Test if X-Client-Cert header is accepted by the target application curl -H "X-Client-Cert: <public_cert>" https://target-app.example.com/protected-endpoint Inspect request headers reaching the application (requires access to application logs or a debugging endpoint)
Exploit: (Educational Purposes!)
Step 1: Obtain the public certificate of a target application instance Step 2: Spoof the X-Client-Cert header to bypass authorization curl -H "X-Client-Cert: <obtained_public_cert>" https://target-app.example.com/protected-endpoint
Protection: from this CVE
- Upgrade to Steeltoe 4.3.0 or later.
- Restrict `UseCertificateForwarding` to trusted proxy source IPs using `ForwardedHeadersOptions.KnownProxies` and
KnownNetworks. - Change the forwarding header to `X-Forwarded-Client-Cert` so that Cloud Foundry Gorouter and Envoy header stripping mechanisms apply to inbound untrusted requests.
- Add a secondary authorization layer, such as a shared secret or mutual TLS at the proxy layer, for sensitive endpoints.
- 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.
Impact:
An 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.
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Sources:
Reported By: github.com
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