not 100% specific for MediaWiki, but be informed
*** to whom it may concern ***
Every version of GnuTLS found to be vulnerable to certification bypass.
See http://packetstormsecurity.com/files/125521/GNU-Transport-Layer-Security-Lib... and look on Twitter for gnutls
The relevant patch appears to be https://www.gitorious.org/gnutls/gnutls/commit/6aa26f78150ccbdf0aec1878a41c1...