CoreWCF up to 1.8.0/1.9.0 SAML Token Validation downgrade

Summaryinfo

A vulnerability, which was classified as critical, has been found in CoreWCF up to 1.8.0/1.9.0. This vulnerability affects unknown code of the component SAML Token Validation. The manipulation leads to downgrade. This vulnerability is referenced as CVE-2026-54781. Remote exploitation of the attack is possible. No exploit is available.

Detailsinfo

A vulnerability was found in CoreWCF up to 1.8.0/1.9.0 and classified as critical. This issue affects an unknown functionality of the component SAML Token Validation. The manipulation with an unknown input leads to a downgrade vulnerability. Using CWE to declare the problem leads to CWE-757. A protocol or its implementation supports interaction between multiple actors and allows those actors to negotiate which algorithm should be used as a protection mechanism such as encryption or authentication, but it does not select the strongest algorithm that is available to both parties. Impacted is confidentiality, integrity, and availability. The summary by CVE is:

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.

The advisory is shared at github.com. The identification of this vulnerability is CVE-2026-54781 since 06/16/2026. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. Neither technical details nor an exploit are publicly available. MITRE ATT&CK project uses the attack technique T1562.010 for this issue.

Upgrading to version 1.8.1 or 1.9.1 eliminates this vulnerability.

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Productinfo

Name

• CoreWCF

Version

• 1.0
• 1.1
• 1.2
• 1.3
• 1.4
• 1.5
• 1.6
• 1.7
• 1.8
• 1.8.0
• 1.9.0

Website

• Product: https://github.com/CoreWCF/CoreWCF/

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Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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