XDM in XFree86 3.3 and 3.3.3 generates easily guessable cookies using gettimeofday() when compiled with the HasXdmXauth option, which allows remote attackers to gain unauthorized access to the X display via a brute force attack.
https://exchange.xforce.ibmcloud.com/vulnerabilities/6808
https://euvd.enisa.europa.eu/vulnerability/EUVD-2001-1067
http://www.securityfocus.com/bid/2985