CRL Critical Extension Bypass in wolfSSL

Executive Summary

This vulnerability is a CRL (Certificate Revocation List) critical extension bypass in the ParseCRL_Extensions function. It occurs because critical extensions in a CRL are not properly enforced, which means that a specially crafted CRL containing an unhandled critical extension can be accepted as valid. This issue only affects builds where CRL support is enabled and the crafted CRL has a trusted signature when parsed.

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Impact Analysis

The impact of this vulnerability is that an attacker could present a crafted CRL with unhandled critical extensions that bypass normal validation checks. This could lead to the acceptance of revoked certificates as valid, potentially undermining the security of systems relying on CRL checks for certificate revocation status.

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Compliance Impact

The vulnerability allows a crafted Certificate Revocation List (CRL) with an unhandled critical extension to be accepted, which violates the enforcement requirements specified in RFC 5280 section 5.2. Since critical extensions must be properly recognized and enforced, this flaw could lead to improper validation of certificate revocation status.

Improper enforcement of CRL critical extensions may undermine the integrity of certificate validation processes, potentially impacting the security controls required by standards like GDPR and HIPAA that mandate strong cryptographic and identity verification measures.

By accepting CRLs with unrecognized critical extensions, systems may fail to properly revoke compromised or invalid certificates, increasing the risk of unauthorized access or data breaches, which could lead to non-compliance with these regulations.

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Detection Guidance

Detection of this vulnerability involves identifying Certificate Revocation Lists (CRLs) that contain unrecognized critical extensions which are improperly accepted by affected wolfSSL builds.

Since the vulnerability is related to parsing CRLs with unhandled critical extensions, one approach is to inspect CRLs used by your system or network for such extensions.

Commands or tools that parse and analyze CRLs according to RFC 5280 can be used to detect unrecognized critical extensions. For example, using OpenSSL commands to inspect CRLs might help identify suspicious or malformed CRLs.

• openssl crl -in <crl_file> -text -noout
• Look for critical extensions in the output and verify if any are unrecognized or unexpected.

However, specific wolfSSL commands or detection scripts are not provided in the available resources.

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Mitigation Strategies

The immediate mitigation step is to update the wolfSSL library to a version that includes the security fix for CVE-2026-6450.

The fix involves rejecting CRLs that contain unrecognized critical extensions, ensuring compliance with RFC 5280 section 5.2.

Applying the patch or upgrading to the fixed version will prevent acceptance of crafted CRLs with unhandled critical extensions.

Additionally, reviewing and validating CRLs used in your environment to ensure they do not contain unrecognized critical extensions can help reduce risk.

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