Mozilla Thunderbird is "an open source electronic mail client and news reader. Multipurpose Internet Message Extensions (MIME) is a standard that defines how non-text attachments and other data are handled in electronic mail. The external-body MIME type is used for retrieving a resource that is referenced in the message, such as an attachment". Remote exploitation of a heap based buffer overflow vulnerability in Mozilla Organization's Thunderbird could allow an attacker to execute arbitrary code with the privileges of the current user.

http://www.securiteam.com/securitynews/5JP0L20NFS.html