CVE-2026-4720

Name	CVE-2026-4720
Description	Memory safety bugs present in Firefox ESR 140.8, Thunderbird ESR 140.8, Firefox 148 and Thunderbird 148. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability affects Firefox < 149, Firefox ESR < 140.9, Thunderbird < 149, and Thunderbird < 140.9.
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
firefox (PTS)	sid	148.0.2-1	vulnerable
firefox-esr (PTS)	bullseye	115.14.0esr-1~deb11u1	vulnerable
	bullseye (security)	140.8.0esr-1~deb11u1	vulnerable
	bookworm	128.14.0esr-1~deb12u1	vulnerable
	bookworm (security)	140.8.0esr-1~deb12u1	vulnerable
	trixie (security), trixie	140.8.0esr-1~deb13u1	vulnerable
	forky	140.8.0esr-1	vulnerable
	sid	140.9.0esr-1	fixed
thunderbird (PTS)	bullseye	1:115.12.0-1~deb11u1	vulnerable
	bullseye (security)	1:140.8.0esr-1~deb11u1	vulnerable
	bookworm	1:140.6.0esr-1~deb12u1	vulnerable
	bookworm (security)	1:140.8.0esr-1~deb12u1	vulnerable
	trixie (security), trixie	1:140.8.0esr-1~deb13u1	vulnerable
	forky, sid	1:140.8.0esr-1	vulnerable

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

Package	Type	Release	Fixed Version
firefox	source	(unstable)	(unfixed)
firefox-esr	source	(unstable)	140.9.0esr-1
thunderbird	source	(unstable)	(unfixed)

Notes

https://www.mozilla.org/en-US/security/advisories/mfsa2026-20/#CVE-2026-4720
https://www.mozilla.org/en-US/security/advisories/mfsa2026-22/#CVE-2026-4720
https://www.mozilla.org/en-US/security/advisories/mfsa2026-24/#CVE-2026-4720