libgadu before 1.12.0 does not verify X.509 certificates from SSL servers, which allows man-in-the-middle attackers to spoof servers.
https://security.gentoo.org/glsa/201508-02
https://lists.fedoraproject.org/pipermail/package-announce/2013-December/125143.html
https://bugzilla.redhat.com/show_bug.cgi?id=1025718
http://www.securityfocus.com/bid/63473
http://www.openwall.com/lists/oss-security/2013/10/31/5
http://www.mandriva.com/security/advisories?name=MDVSA-2014:185
http://www.mail-archive.com/libgadu-devel%40lists.ziew.org/msg01017.html