When using the CAS Proxy ticket authentication from Spring Security 3.1 through 3.1.6 and 3.2.x through 3.2.4 a malicious CAS Service could trick another CAS Service into authenticating a proxy ticket that was not associated. This is due to the fact that the proxy ticket authentication uses the information from the HttpServletRequest which is populated based upon untrusted information within the HTTP request. This means if there are access control restrictions on which CAS services can authenticate to one another, those restrictions can be bypassed. If users are not using CAS Proxy tickets and not basing access control decisions based upon the CAS Service, then there is no impact to users.
CWE-287 - Improper Authentication
Improper (or broken) authentication attacks are widespread, and have accounted for many of the worst data breaches in recent years. Improper authentication attacks are a class of vulnerabilities where an attacker impersonates a legitimate user by exploiting weaknesses in either session management or credential management to gain access to the user’s account. This can result in disclosure of sensitive information, and can lead to system compromise, theft, identity theft, and fraud.