CVE-2026-14899

Name	CVE-2026-14899
Description	The code to parse MIME headers for display when forwarding a message (if the setting to view all headers was enabled) had an off-by-one error, allowing a single byte to be read from the memory after the buffer for the headers, and potentially crashing Thunderbird. This vulnerability was fixed in Thunderbird 153 and Thunderbird 140.13.
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)	bullseye	1:115.12.0-1~deb11u1	vulnerable
	bullseye (security)	1:140.12.0esr-1~deb11u1	vulnerable
	bookworm, bookworm (security)	1:140.12.0esr-1~deb12u1	vulnerable
	trixie (security), trixie	1:140.12.0esr-1~deb13u1	vulnerable
	forky, sid	1:140.12.0esr-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)

https://www.mozilla.org/en-US/security/advisories/mfsa2026-72/#CVE-2026-14899