Maksim Otstavnov discovered that the Wocky submodule used by telepathy-gabble, the Jabber/XMPP connection manager for the Telepathy framework, does not respect the tls-required flag on legacy Jabber servers. A network intermediary could use this vulnerability to bypass TLS verification and perform a man-in-the-middle attack.
For the oldstable distribution (squeeze), this problem has been fixed in version 0.9.15-1+squeeze2.
For the stable distribution (wheezy), this problem has been fixed in version 0.16.5-1+deb7u1.
For the testing distribution (jessie) and the unstable distribution (sid), this problem has been fixed in version 0.16.6-1.
We recommend that you upgrade your telepathy-gabble packages.