Multiple vulnerabilities have been reported in Thunderbird, which can be exploited by malicious people to bypass certain security restrictions, conduct cross-site scripting and HTTP response smuggling attacks, and potentially compromise a user's system.

For more information, see vulnerabilities #1, #2, #3, #5, #6, #7, and #9 in:
SA20376

Successful exploitation of some of the vulnerabilities requires that JavaScript is enabled (not enabled by default).

The following vulnerability has also been reported:

The vulnerability is caused due to a double-free error within the processing of large VCards with invalid base64 characters. This may be exploited to execute arbitrary code.

Solution
Update to version 1.5.0.4.
Further details available to Secunia VIM customers

Provided and/or discovered by
Masatoshi Kimura

Changelog
Further details available to Secunia VIM customers

Original Advisory
http://www.mozilla.org/security/announce/2006/mfsa2006-40.html

Other references
Further details available to Secunia VIM customers

Deep Links
Links available to Secunia VIM customers