Vulnerability · Published Sep 17, 2026 · Assigned by GitHub_M
CVE-2026-81868Steeltoe: Header-forwarded client cert lacks proof of private-key possession
Medium 6.5
In plain English
A medium-severity authentication bypass in security-advisories from SteeltoeOSS. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 16% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| NuGet | steeltoe.security.authorization.certificate | 4.3.0 | GHSA-5mq7-rwhj-4fh9 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| SteeltoeOSS | security-advisories | < 4.3.0 |
Weakness: CWE-288, CWE-295 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N