CVE-2026-4721
9.8
CRITICAL
CVSS 3.1
EPSS 0.03%
Description
Memory safety bugs present in Firefox ESR 115.33, 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 was fixed in Firefox 149, Firefox ESR 115.34, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.
How to fix CVE-2026-4721
To remediate CVE-2026-4721, upgrade the affected package to a fixed version below.
- —upgrade to 140.9.0esr-1~deb11u1 or later
- —upgrade to 1:140.9.0esr-1~deb11u1 or later
Is CVE-2026-4721 being exploited?
Low — EPSS is 0.0%, meaning exploitation activity has not been observed at scale.
Affected packages (2)
- from 0, < 140.9.0esr-1~deb11u1
- from 0, < 1:140.9.0esr-1~deb11u1
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 3.1 | CRITICAL9.8 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H |