CVE-2026-54781 CoreWCF: SAML SubjectConfirmation methods and holder-of-key proof keys are not enforced
Attackers can bypass SAML authentication in CoreWCF by exploiting missing SubjectConfirmation and holder-of-key validation, allowing unauthorized access.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-54781?
CVE-2026-54781 is a high-severity authentication bypass vulnerability in CoreWCF, published on 8 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
CoreWCF is a port of the service side of Windows Communication Foundation (WCF) to .NET Core. Prior to 1.8.1 and 1.9.1, CoreWCF SAML token validation does not enforce SubjectConfirmation method URIs or holder-of-key proof keys in SamlSecurityTokenHandler, allowing holder-of-key downgrade or custom confirmation method assertions to authenticate a subject without proving authority over the assertion. This issue is fixed in versions 1.8.1 and 1.9.1.
Which versions are affected by CVE-2026-54781?
4 open source packages ship an affected version, including CoreWCF.Primitives.
| Package | Affected | Fixed in |
|---|---|---|
CoreWCF.Primitives NuGet | All versions | 1.8.1 |
CoreWCF.Primitives NuGet | All versions | 1.8.1 |
CoreWCF.Primitives NuGet | From 1.9.0 | 1.9.1 |
CoreWCF.Primitives NuGet | From 1.9.0 | 1.9.1 |
How do I fix CVE-2026-54781?
Upgrade CoreWCF.Primitives to a fixed version for your release line: 1.8.1 or 1.9.1.
Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2026-54781 being exploited?
There is no known exploitation of CVE-2026-54781 in the wild and no public exploit code.
Sources
Also known as GHSA-48pq-2xq3-c2m4.