Memory safety bugs were reported in Thunderbird 45.7. Some of these bugs showed evidence of memory corruption and we presume that with enough effort that some of these could be exploited to run arbitrary code. This vulnerability affects Firefox < 52, Firefox ESR < 45.8, Thunderbird < 52, and Thunderbird < 45.8.
http://rhn.redhat.com/errata/RHSA-2017-0459.html
http://rhn.redhat.com/errata/RHSA-2017-0461.html
http://rhn.redhat.com/errata/RHSA-2017-0498.html
https://security.gentoo.org/glsa/201705-06
https://security.gentoo.org/glsa/201705-07
https://www.debian.org/security/2017/dsa-3805
https://www.debian.org/security/2017/dsa-3832
https://www.mozilla.org/security/advisories/mfsa2017-05/
https://www.mozilla.org/security/advisories/mfsa2017-06/
https://www.mozilla.org/security/advisories/mfsa2017-07/