Alt-N MDaemon's WorldClient Username Enumeration Vulnerability
Software: Alt-N MDaemon v13.0.3 and prior versions
Vendor: http://www.altn.com/
Vulnerability Type: Username Enumeration
Remote: Yes
Local: No
Discovered: 14 September 2012
Reported: 19 December 2012
Disclosed: 18 February 2013
Whitepaper: Pwning_MDaemon.pdf
VULNERABILITY DESCRIPTION:
Alt-N WorldClient is prone to a username-enumeration weakness by querying the user's Free-Busy schedule. The DTSTART and DTEND parameters in the returned FBData.vfb file, may indicate whether an email address/username is valid or not.
Attackers may exploit this weakness to discern valid usernames. This may aid them in brute-force password cracking or other attacks.
Alt-N MDaemon v13.0.3 & v12.5.6 were tested and found vulnerable; other versions may also be affected.
PoC Exploit:
http://www.example.com:3000/WorldClient.dll?View=fbinfo&User=This email address is being protected from spambots. You need JavaScript enabled to view it.
For valid email accounts the DTSTART and DTEND values in the .vfb file start with a recent date backwards (e.g. 20120505) whereas for invalid ones the date is 19801231.
