expect before 5.32 searches for its libraries in /var/tmp before other directories, which could allow local users to gain root privileges via a Trojan horse library that is accessed by mkpasswd.

mkpasswd in expect 5.2.8, as used by Red Hat Linux 6.2 through 7.0, seeds its random number generator with its process ID, which limits the space of possible seeds and makes it easier for attackers to conduct brute force password attacks.