CVE-2026-81868 Steeltoe: Header-forwarded client cert lacks proof of private-key possession
Attackers can spoof client certificates to bypass organization and space authorization policies in Steeltoe applications if trusted proxy restrictions are not configured.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-81868?
CVE-2026-81868 is a medium-severity authentication bypass vulnerability in SteeltoeOSS security-advisories, published on 17 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
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.
Which versions are affected by CVE-2026-81868?
2 open source packages ship an affected version, including Steeltoe.Security.Authorization.Certificate.
| Package | Affected | Fixed in |
|---|---|---|
Steeltoe.Security.Authorization.Certificate NuGet | All versions | 4.3.0 |
Steeltoe.Security.Authorization.Certificate NuGet | All versions | 4.3.0 |
How do I fix CVE-2026-81868?
Upgrade Steeltoe.Security.Authorization.Certificate to 4.3.0 or later.
Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2026-81868 being exploited?
There is no known exploitation of CVE-2026-81868 in the wild and no public exploit code.
Sources
Also known as GHSA-5mq7-rwhj-4fh9.