SAML Token Validation Bypass in CoreWCF

Compliance Impact

This vulnerability allows attackers to bypass authentication in SAML-based systems by accepting SAML assertions without proper validation of SubjectConfirmation methods or holder-of-key proof keys. This can lead to unauthorized access and acceptance of identity claims without proof of authority.

Such unauthorized access and improper authentication can compromise confidentiality and integrity of sensitive data, which are critical requirements under common standards and regulations like GDPR and HIPAA.

Therefore, if an organization uses affected CoreWCF versions for authentication in systems handling regulated data, this vulnerability could lead to non-compliance with these regulations due to insufficient verification of user identity and potential data breaches.

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Executive Summary

This vulnerability exists in CoreWCF, a port of Windows Communication Foundation to .NET Core. Before versions 1.8.1 and 1.9.1, the SAML token validation in CoreWCF's SamlSecurityTokenHandler did not properly enforce SubjectConfirmation method URIs or holder-of-key proof keys. This flaw allows an attacker to perform a holder-of-key downgrade or use custom confirmation method assertions to authenticate a subject without actually proving authority over the assertion.

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Impact Analysis

The vulnerability can allow unauthorized authentication by bypassing proper validation of SAML tokens. This means an attacker could impersonate a legitimate user or service without proving they have the correct cryptographic keys, potentially leading to unauthorized access to sensitive systems or data.

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Mitigation Strategies

To mitigate this vulnerability, upgrade CoreWCF to version 1.8.1 or 1.9.1, where the issue with SAML token validation is fixed.

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Detection Guidance

This vulnerability involves improper validation of SAML SubjectConfirmation methods and holder-of-key proof keys in CoreWCF's SamlSecurityTokenHandler. Detection would involve monitoring SAML assertions processed by your CoreWCF service to identify assertions that use unrecognized confirmation methods or holder-of-key assertions missing the required KeyInfo proof key.

Since the vulnerability is in the token validation logic within CoreWCF, direct network detection commands are not explicitly provided in the available resources. However, you can detect exploitation attempts by enabling detailed logging or tracing in your CoreWCF application to capture SecurityTokenValidationException errors related to unrecognized confirmation methods or missing KeyInfo elements.

Specifically, look for error messages such as "SAMLHolderOfKeyRequiresKeyInfo" or "SAMLUnrecognizedConfirmationMethod" in your application logs, which indicate failed validation attempts due to this vulnerability.

No specific command-line tools or network scanning commands are provided in the resources. Detection is primarily through application-level logging and validation exceptions.

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