Security research firm iDefense reported that researcher regenrecht discovered a heap-based buffer overflow vulnerability in Mozilla mail code which could potentially allow an attacker to run arbitrary code. The vulnerability is caused by allocating a buffer that can be three bytes too small in certain cases when viewing an email message with an external MIME body.
Users can prevent the vulnerable code from being triggered by setting the "mailnews.display.disallow_mime_handlers" property to any value greater than or equal to 3.