A use-after-free vulnerability can occur when flushing and resizing layout because the "PressShell" object has been freed while still in use. This results in a potentially exploitable crash during these operations. This vulnerability affects Firefox < 57, Firefox ESR < 52.5, and Thunderbird < 52.5.
https://www.mozilla.org/security/advisories/mfsa2017-26/
https://www.mozilla.org/security/advisories/mfsa2017-25/
https://www.mozilla.org/security/advisories/mfsa2017-24/
https://www.debian.org/security/2017/dsa-4075
https://www.debian.org/security/2017/dsa-4061
https://www.debian.org/security/2017/dsa-4035
https://lists.debian.org/debian-lts-announce/2017/12/msg00001.html
https://lists.debian.org/debian-lts-announce/2017/11/msg00018.html
https://bugzilla.mozilla.org/show_bug.cgi?id=1412252
https://bugzilla.mozilla.org/show_bug.cgi?id=1406750
https://access.redhat.com/errata/RHSA-2017:3372
https://access.redhat.com/errata/RHSA-2017:3247