Denial of Service in wolfSSL via SAN Validation Bypass

Executive Summary

This vulnerability is in wolfSSL versions 5.9.2, 5.9.4, and the master branch. It involves improper certificate validation in the ConfirmNameConstraints() function. When a certificate lacks a Subject Alternative Name (SAN) extension, the function incorrectly applies DNS name constraints to the subject Common Name (CN). This causes legitimate certificates issued without a SAN under a CA with DNS name constraints to be rejected, leading to failed TLS connections and potential denial of service.

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Detection Guidance

To detect this vulnerability, check the wolfSSL version in use with commands like 'wolfssl --version' or 'openssl s_client -connect <host>:<port> -showcerts'. If using versions 5.9.2, 5.9.4, or the master branch, the system is potentially vulnerable.

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Impact Analysis

This vulnerability can cause legitimate servers to become unreachable due to failed TLS connections. It affects name-constrained Public Key Infrastructures (PKIs) where certificates are issued without a SAN. Users relying on wolfSSL for TLS connections may experience disruptions if their certificates are incorrectly rejected.

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Compliance Impact

This vulnerability may impact compliance with standards requiring proper certificate validation, such as GDPR's data protection measures or HIPAA's secure communication requirements. The improper rejection of valid certificates due to the ConfirmNameConstraints() flaw could disrupt TLS connections, potentially leading to unauthorized access or data breaches if systems fail to enforce secure communication channels.

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Mitigation Strategies

Immediately upgrade wolfSSL to a patched version or apply the latest security patches from wolfSSL. Avoid using versions 5.9.2, 5.9.4, or the master branch until fixed. Review certificate configurations to ensure SAN extensions are present where required.

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