Security researchers Tyson Smith and Jesse Schwartzentruber of the BlackBerry Security Automated Analysis Team used the Address Sanitizer tool while fuzzing to discover a user-after-free in the functions for synthetic mouse movement handling. Security researcher Atte Kettunen from OUSPG also reported a variant of the same flaw. This issue leads to a potentially exploitable crash.
In general these flaws cannot be exploited through email in the Thunderbird and Seamonkey products because scripting is disabled, but are potentially a risk in browser or browser-like contexts.