CVE-2026-84642

Name	CVE-2026-84642
Description	The values of the mail.allowed_attachment_hostnames advanced config setting were used in a regular expression without escaping. For some possible valid hostnames, this could allow certain unintended hostnames to also match and serve remote attachments. This vulnerability was fixed in Thunderbird 155 and Thunderbird 153.2.
Source	CVE (at NVD; CERT, ENISA, LWN, oss-sec, fulldisc, Debian ELTS, 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)	bookworm	1:140.12.0esr-1~deb12u1	fixed
	bookworm (security)	1:140.14.0esr-1~deb12u1	fixed
	trixie	1:140.12.0esr-1~deb13u1	fixed
	trixie (security)	1:140.14.0esr-1~deb13u1	fixed
	forky, sid	1:140.14.0esr-1	fixed

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

Package	Type	Release	Fixed Version	Urgency	Origin	Debian Bugs
thunderbird	source	(unstable)	(not affected)

- thunderbird <not-affected> (Thunderbird ESR140 series not affected)
https://www.mozilla.org/en-US/security/advisories/mfsa2026-86/#CVE-2026-84642