PAM 0.76 treats a disabled password as if it were an empty (null) password, which allows local and remote attackers to gain privileges as disabled users.
Linux PAM modules allow local users to gain root access using temporary files.
The SELinux version of PAM before 0.78 r3 allows local users to perform brute force password guessing attacks via unixchkpwd, which does not log failed guesses or delay its responses.