phpCAS before 1.3.2 does not verify that the server hostname matches a domain name in the subject's Common Name (CN) or subjectAltName field of the X.509 certificate, which allows man-in-the-middle attackers to spoof SSL servers via an arbitrary valid certificate.
Jasig phpCAS version 1.3.4 is vulnerable to an authentication bypass in the validateCAS20 function when configured to authenticate against an old CAS server.