fontconfig before 2.12.1 does not validate offsets, which allows local users to trigger arbitrary free calls and consequently conduct double free attacks and execute arbitrary code via a crafted cache file.
rhn.redhat.com/errata/RHSA-2016-2601.html
www.debian.org/security/2016/dsa-3644
www.securityfocus.com/bid/92339
www.ubuntu.com/usn/USN-3063-1
cgit.freedesktop.org/fontconfig/commit/?id=7a4a5bd7897d216f0794ca9dbce0a4a5c9d14940
lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/6CJ45VRAMCIISHOVKFVOQYQUSTUJP7FC/
lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/GGOS4YYB7UYAWX5AEXJZHDIX4ZMSXSW5/
lists.freedesktop.org/archives/fontconfig/2016-August/005792.html