process_certificate in tls1.c in Cameron Hamilton-Rich axTLS through 2.1.5 has a Buffer Overflow via a crafted TLS certificate handshake message with zero certificates.
https://seclists.org/bugtraq/2019/Nov/44
http://packetstormsecurity.com/files/155500/axTLS-2.1.5-Denial-Of-Service.html