CVE-2026-84143

Name	CVE-2026-84143
Description	Internally found bugs present in Thunderbird 154, Thunderbird ESR 153.1 and Thunderbird ESR 140.14. Some of these bugs showed evidence of memory corruption or another security-relevant defect and we presume that with enough effort some of these could have been exploited. This vulnerability was fixed in Firefox 155, Firefox ESR 140.15, Firefox ESR 153.2, Thunderbird 155, Thunderbird 140.15, 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)
References	DSA-6481-1

Vulnerable and fixed packages

The table below lists information on source packages.

Source Package	Release	Version	Status
firefox (PTS)	sid	155.0-1	fixed
firefox-esr (PTS)	bookworm	140.12.0esr-1~deb12u1	vulnerable
	bookworm (security)	140.14.0esr-1~deb12u1	vulnerable
	trixie	140.12.0esr-1~deb13u1	vulnerable
	trixie (security)	140.14.0esr-1~deb13u1	vulnerable
	forky	140.14.0esr-2	vulnerable
	sid	140.15.0esr-1	fixed
thunderbird (PTS)	bookworm	1:140.12.0esr-1~deb12u1	vulnerable
	bookworm (security)	1:140.14.0esr-1~deb12u1	vulnerable
	trixie	1:140.12.0esr-1~deb13u1	vulnerable
	trixie (security)	1:140.14.0esr-1~deb13u1	vulnerable
	forky	1:140.14.0esr-1	vulnerable
	sid	1:153.2.0esr-1	fixed

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

Package	Type	Release	Fixed Version	Origin
firefox	source	(unstable)	155.0-1
firefox-esr	source	trixie	140.15.0esr-1~deb13u1	DSA-6481-1
firefox-esr	source	(unstable)	140.15.0esr-1
thunderbird	source	(unstable)	1:153.2.0esr-1

Notes

https://www.mozilla.org/en-US/security/advisories/mfsa2026-82/#CVE-2026-84143
https://www.mozilla.org/en-US/security/advisories/mfsa2026-84/#CVE-2026-84143
https://www.mozilla.org/en-US/security/advisories/mfsa2026-87/#CVE-2026-84143