daemon/Greeter.cpp in sddm before 0.13.0 does not properly disable the KDE crash handler, which allows local users to gain privileges by crashing a greeter when using certain themes, as demonstrated by the plasma-workspace breeze theme.
https://github.com/sddm/sddm/wiki/0.13.0-Release-Announcement
https://github.com/sddm/sddm/commit/4cfed6b0a625593fb43876f04badc4dd99799d86
http://www.securityfocus.com/bid/77099
http://www.openwall.com/lists/oss-security/2015/10/14/2
http://lists.fedoraproject.org/pipermail/package-announce/2015-November/171443.html