Package Instance

By crafting a malformed file name for an attachment in a multipart
message, an attacker can trick Thunderbird into including a
directory listing of /tmp when the message is forwarded or edited
as a new message. This vulnerability could allow attackers to
disclose sensitive information from the victim's system. This
vulnerability is not limited to Linux; similar behavior has been
observed on Windows as well.

When an email contains multiple attachments with external links
via the X-Mozilla-External-Attachment-URL header, only the last
link is shown when hovering over any attachment. Although the
correct link is used on click, the misleading hover text could
trick users into downloading content from untrusted sources.

Thunderbird processes the X-Mozilla-External-Attachment-URL header
to handle attachments which can be hosted externally. When an
email is opened, Thunderbird accesses the specified URL to 
determine file size, and navigates to it when the user clicks the
attachment. Because the URL is not validated or sanitized, it can
reference internal resources like chrome:// or SMB share file:// links,
potentially leading to hashed Windows credential leakage and opening the
door to more serious security issues.