Executive Summary

This vulnerability exists in the wolfSSL OpenSSL compatibility layer, specifically in the function wolfSSL_X509_verify_cert. It allows an attacker to supply a certificate chain where the leaf certificate's signature is not properly checked if the attacker includes an untrusted intermediate certificate marked with Basic Constraints CA:FALSE that is legitimately signed by a trusted root.

An attacker who has obtained any leaf certificate from a trusted Certificate Authority (for example, a free Domain Validation certificate from Let's Encrypt) can exploit this flaw to forge a certificate for any subject name with any public key and arbitrary signature bytes. The verification function incorrectly returns success (WOLFSSL_SUCCESS / X509_V_OK) despite the forged certificate.

This issue only affects applications that use the OpenSSL compatibility API of wolfSSL directly, such as integrations of wolfSSL into nginx and haproxy. The native wolfSSL TLS handshake path is not vulnerable.

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Impact Analysis

This vulnerability can allow an attacker to forge certificates that appear valid to the affected verification function, potentially enabling man-in-the-middle attacks, impersonation of any subject name, and unauthorized access to encrypted communications.

Because the forged certificates are accepted as valid, attackers could intercept or manipulate TLS traffic in applications using the vulnerable wolfSSL OpenSSL compatibility API, such as nginx or haproxy integrations, compromising confidentiality and integrity.

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Compliance Impact

This vulnerability allows an attacker to forge certificates that appear valid to applications using the wolfSSL OpenSSL compatibility API, potentially enabling unauthorized access or impersonation.

Such unauthorized access or impersonation could lead to violations of data protection and security requirements mandated by standards like GDPR and HIPAA, which require strong authentication and secure communications.

Therefore, organizations using affected software without mitigation may face increased risk of non-compliance due to weakened certificate validation.

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