CVE 2006-1045
The HTML rendering engine in Mozilla Thunderbird 1.5, when "Block loading of remote images in mail messages" is enabled, does not properly block external images from inline HTML attachments, which could allow remote attackers to obtain sensitive information, such as application version or IP address, when the user reads the email and the external image is accessed.
See the 
CVE page on Mitre.org
for more details.
