Security researcher Abhishek Arya (Inferno) of the Google Chrome Security Team used the Address Sanitizer tool to report an out-of-bounds read and an out-of-bounds write when rendering an improperly formatted SVG graphic. This could potentially allow the attacker to read uninitialized memory.
In general this flaw cannot be exploited through email in the Thunderbird product because scripting is disabled, but is potentially a risk in browser or browser-like contexts.