CVE-2026-4720 PUBLISHED

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 and Firefox ESR < 140.9.

• Christian Holler, Gabriele Svelto, Tom Schuster and the Mozilla Fuzzing Team

• Memory safety bugs fixed in Firefox ESR 140.9, Thunderbird ESR 140.9, Firefox 149 and Thunderbird 149
• https://www.mozilla.org/security/advisories/mfsa2026-20/
• https://www.mozilla.org/security/advisories/mfsa2026-22/