A use-after-free vulnerability can occur when reading an image observer during frame reconstruction after the observer has been freed. This results in a potentially exploitable crash. This vulnerability affects Thunderbird < 52.3, Firefox ESR < 52.3, and Firefox < 55.
www.securityfocus.com/bid/100202
www.securitytracker.com/id/1039124
access.redhat.com/errata/RHSA-2017:2456
access.redhat.com/errata/RHSA-2017:2534
bugzilla.mozilla.org/show_bug.cgi?id=1376087
security.gentoo.org/glsa/201803-14
www.debian.org/security/2017/dsa-3928
www.debian.org/security/2017/dsa-3968
www.mozilla.org/security/advisories/mfsa2017-18/
www.mozilla.org/security/advisories/mfsa2017-19/
www.mozilla.org/security/advisories/mfsa2017-20/