WebCalendar 1.0.1 to 1.0.3 generates different error messages depending on whether or not a username is valid, which allows remote attackers to enumerate valid usernames.
https://exchange.xforce.ibmcloud.com/vulnerabilities/26262
http://www.securityfocus.com/bid/17853
http://www.securityfocus.com/archive/1/433077/100/0/threaded
http://www.securityfocus.com/archive/1/433053/100/0/threaded
http://www.debian.org/security/2006/dsa-1056