Under the WOLFSSL_SMALL_CERT_VERIFY build option, wolfSSL's ProcessPeerCertParse() function performs certificate signature verification separately from parsing to reduce peak memory usage. However, it merges the signature verification result back only if parsing succeeds, causing signature verification errors to be suppressed if parsing fails. Since validity-date and other certificate checks occur only after signature confirmation, this inversion breaks the intended precedence that allows date errors to override signature errors. An attacker can exploit this by presenting a self-signed certificate with the expected subject name, the trusted CA's subject as issuer, arbitrary signature bytes, a validity window in the past, and their own key pair. The application must install a verify callback that returns success for date errors to trigger the vulnerability. Without such a callback, the handshake fails correctly. The vulnerability affects wolfSSL builds with WOLFSSL_SMALL_CERT_VERIFY enabled, which is off by default and only reachable via specific low-resource build options. TLS 1.2, TLS 1.3, and DTLS are affected in both client and server directions. If a forged certificate is cached, the context or process must be restarted to clear it.

An attacker can bypass certificate signature verification by exploiting the inversion of signature and parse error handling in wolfSSL when WOLFSSL_SMALL_CERT_VERIFY is enabled and a verify callback overrides date errors. This allows the attacker to impersonate a trusted CA or entity using a self-made certificate without needing the real CA's private key or compromising the PKI. The vulnerability impacts the integrity of TLS and DTLS connections, potentially allowing man-in-the-middle or impersonation attacks. However, the vulnerability requires specific build configurations and application-level verify callback behavior, limiting its exposure.

This vulnerability only affects wolfSSL builds with WOLFSSL_SMALL_CERT_VERIFY enabled, which is off by default and not enabled by default in common build presets. Applications should avoid enabling WOLFSSL_SMALL_CERT_VERIFY unless necessary. Additionally, applications should not use verify callbacks that override date errors by returning success for ASN_BEFORE_DATE_E or ASN_AFTER_DATE_E. If a deployment is exposed and a forged certificate is cached, restarting the wolfSSL context or process clears the cache. No official patch or fix is indicated in the provided data; patch status is not yet confirmed — check the vendor advisory for current remediation guidance.