A flaw in the wolfSSL OpenSSL compatibility layer allows a certificate chain to be accepted when the leaf certificate's signature is not verified. When an application supplies an untrusted intermediate with the Basic Constraints field set to CA:FALSE that is still legitimately signed by a trusted root, the verification function returns success even though the leaf was not properly checked. As a result an attacker who can obtain any leaf certificate from a public CA, for example a free DV certificate from Let’s Encrypt, can create a forged certificate for any subject and public key. The function then reports success, enabling the attacker to impersonate a legitimate server or client and potentially carry out man‑in‑the‑middle attacks, credential theft, or data exfiltration. Only the OpenSSL compatibility API is affected; the native wolfSSL TLS handshake path remains secure.

The vulnerability affects the wolfSSL library itself, specifically versions that expose the OpenSSL compatibility API. Applications that integrate wolfSSL via this API—such as nginx and haproxy—are susceptible. No specific product version details are provided in the input.

The CVSS score of 8.6 indicates a high severity. EPSS data is unavailable and the issue is not listed in the CISA KEV catalog, suggesting limited observed exploitation. The likely attack vector involves an attacker delivering a crafted certificate chain to an application using the affected API, exploiting the missing leaf signature check to establish a TLS session with the attacker’s forged credentials. Because the flaw operates without interacting with the application’s native certificate verification path, it can be triggered remotely by simply presenting the forged chain during the TLS handshake.