openssl: man-in-the-middle

During certificate verification, OpenSSL will attempt to find an
alternative certificate chain if the first attempt to build such a chain
fails. An error in the implementation of this logic can mean that an
attacker could cause certain checks on untrusted certificates to be
bypassed, such as the CA flag, enabling them to use a valid leaf
certificate to act as a CA and "issue" an invalid certificate.

This issue will impact any application that verifies certificates
including SSL/TLS/DTLS clients and SSL/TLS/DTLS servers using client
authentication.