my.activation.php3 in F5 FirePass 5.4 through 5.5.1 and 6.0 displays different error messages for failed login attempts with a valid username than for those with an invalid username, which allows remote attackers to confirm the validity of an LDAP account.
https://tech.f5.com/home/solutions/sol6923.html
http://www.securityfocus.com/bid/21957
http://www.mnin.org/advisories/2007_firepass.pdf
http://secunia.com/advisories/23627
http://lists.grok.org.uk/pipermail/full-disclosure/2007-January/051651.html