Apache Tomcat is a servlet container.
It was found that when an application used FORM authentication, along with another component that calls request.setUserPrincipal() before the call to FormAuthenticator#authenticate() (such as the Single-Sign-On valve), it was possible to bypass the security constraint checks in the FORM authenticator by appending "/j_security_check" to the end of a URL. A remote attacker with an authenticated session on an affected application could use this flaw to circumvent authorization controls, and thereby access resources not permitted by the roles associated with their authenticated session. (CVE-2012-3546)
Warning: Before applying the update, back up your existing JBoss Enterprise Web Server installation (including all applications and configuration files).
Users of Tomcat should upgrade to these updated packages, which resolve this issue. Tomcat must be restarted for this update to take effect.