ldm in Linux Terminal Server Project (LTSP) 0.99 and 2 passes the -ac option to the X server on each LTSP client, which allows remote attackers to connect to this server via TCP port 6006 (aka display :6).
https://exchange.xforce.ibmcloud.com/vulnerabilities/42080
http://www.securitytracker.com/id?1019940
http://www.securityfocus.com/bid/28960
http://www.openwall.com/lists/oss-security/2008/03/12/3
http://www.openwall.com/lists/oss-security/2008/03/11/2
http://www.debian.org/security/2008/dsa-1561
http://secunia.com/advisories/30099