Kali Linux Mailing List Website Hacked By Libyan Hackers

One of the best and favorite Security pentesting operating is Kali Linux, which is the advanced version of the BackTrack. The OS is specially designed for the security professional and owned by Offensive Security Team. The OS comes with more than 300 security testing tools pre-installed.
Just some hours ago, a Libyan hacker named "(The GreaT TeAm)" hacked and defaced the mailing list domain (http://lists.kali.org/cgi-bin/mailman/listinfo/kali) of Kali Linux. On the deface page hackers haven't written any message, just with greeting text "h4x3d by The GreaT TeAm" and "Libyan H4x0rz :D".

At the time of writing the homepage of the mailing list domain was showing the two lists-

Kali  with description Hacked By The GreaT TeAm -TGT
Kali-Dev  with description Libyan Hackers

It is not clear how the hackers have managed to add the deface page on the server. May the mailing list site have been compromised or the server has been hacked. In the meantime, the site was still showing the deface page and you can also check the Mirror of the hack at Zone-h.

The GreaT TeAm was the same hacker group who have also hacked the Egyptian Ministry of Information Website two days before, and they also defaced a NATO subdomain.

UPDATE:- 
After Contacting the hacker's team, they reported that the "kali team didn't check the security for mailmanlist.net before they linked their domain "mailmanlist". The mailing list domain of Kali Linux is hosted on the Mailmanlist, and the Mailmanlist website is Vulnerable to Heartbleed vulnerability.

After exploiting the Heartbleed vulnerability, hackers have managed to gain access to the mailman list users' accounts via stolen cookies and then searched for more vulnerable web applications. This allows him to gain the administrative credentials of the Kali Linux Mailing list account.