CVE-2026-54781 in CoreWCF
Summary
by MITRE • 07/09/2026
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.
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Analysis
by VulDB Data Team • 07/09/2026
The vulnerability in CoreWCF relates to insufficient validation of Security Assertion Markup Language (SAML) tokens within the SamlSecurityTokenHandler component, specifically affecting versions prior to 1.8.1 and 1.9.1. This flaw represents a critical security weakness in identity and access management systems that rely on SAML-based authentication mechanisms. The issue stems from the absence of proper enforcement for SubjectConfirmation method URIs and holder-of-key proof keys during token validation processes, creating potential pathways for unauthorized authentication.
The technical flaw manifests when CoreWCF processes SAML tokens without rigorously validating the confirmation methods specified in the token's subject confirmation data. In legitimate SAML implementations, SubjectConfirmation elements should contain specific method URIs that define how the subject's identity is confirmed, and holder-of-key assertions require cryptographic proof that the entity presenting the token actually possesses the private key corresponding to the public key referenced in the assertion. The vulnerability allows attackers to bypass these security checks by submitting tokens with modified or default confirmation methods that do not properly validate possession of keys or adherence to specified confirmation protocols.
This weakness creates significant operational impact within systems utilizing CoreWCF for service communication and authentication. An attacker could potentially exploit this vulnerability to perform unauthorized access by presenting SAML tokens with downgrade confirmation methods that bypass the normal holder-of-key validation requirements. The consequences extend beyond simple authentication bypass, as this flaw could enable privilege escalation attacks where malicious actors gain elevated access rights through manipulated token assertions. Organizations relying on CoreWCF for secure service communication face potential data breaches, unauthorized system access, and compromised identity management frameworks.
The mitigation strategy involves upgrading to CoreWCF versions 1.8.1 or 1.9.1, which implement proper enforcement of SubjectConfirmation method URIs and holder-of-key proof key validation. Security administrators should also conduct thorough assessments of existing SAML token handling processes and ensure all systems are updated to prevent exploitation of this vulnerability. Organizations may need to review their current authentication flows and verify that all token validation components properly enforce cryptographic proof requirements as outlined in the updated security implementations.
This vulnerability aligns with CWE-295 which addresses "Improper Certificate Validation" and relates to ATT&CK technique T1078.004 for Valid Accounts and T1566 for Phishing, as the flaw enables unauthorized authentication through manipulated token assertions. The issue demonstrates the importance of proper cryptographic validation in security token systems and highlights the necessity of maintaining up-to-date security frameworks to prevent downgrade attacks that compromise authentication integrity.