PAM (Pluggable Authentication Modules) is a system security tool that allows system administrators to set an authentication policy without having to recompile programs that handle authentication.
A bug was found in the way PAM's unix_chkpwd helper program validates user passwords when SELinux is enabled. Under normal circumstances, it is not possible for a local non-root user to verify the password of another local user with the unix_chkpwd command. A patch applied that adds SELinux functionality makes it possible for a local user to use brute force password guessing techniques against other local user accounts. The Common Vulnerabilities and Exposures project has assigned the name CVE-2005-2977 to this issue.
All users of pam should upgrade to this updated package, which contains backported patches to correct these issues.