CVE-2025-3522

Name	CVE-2025-3522
Description	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. This vulnerability affects Thunderbird < 137.0.2 and Thunderbird < 128.9.2.
Source	CVE (at NVD; CERT, LWN, oss-sec, fulldisc, Red Hat, Ubuntu, Gentoo, SUSE bugzilla/CVE, GitHub advisories/code/issues, web search, more)

Vulnerable and fixed packages

The table below lists information on source packages.

Source Package	Release	Version	Status
thunderbird (PTS)	bullseye	1:115.12.0-1~deb11u1	vulnerable
	bullseye (security)	1:128.9.0esr-1~deb11u1	vulnerable
	bookworm	1:128.8.0esr-1~deb12u1	vulnerable
	bookworm (security)	1:128.9.0esr-1~deb12u1	vulnerable
	sid, trixie	1:128.9.0esr-1	vulnerable

The information below is based on the following data on fixed versions.

Package	Type	Release	Fixed Version	Urgency	Origin	Debian Bugs
thunderbird	source	(unstable)	(unfixed)

Notes

[bookworm] - thunderbird <postponed> (Fix along with May security release)
https://www.mozilla.org/en-US/security/advisories/mfsa2025-27/#CVE-2025-3522