CVE-2026-4691
9.8
CRITICAL
CVSS 3.1
EPSS 0.04%
Description
Use-after-free in the CSS Parsing and Computation component. 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-2026-4691
To remediate CVE-2026-4691, upgrade the affected package to a fixed version below.
- Debian/firefox-esr—upgrade to 140.9.0esr-1~deb11u1 or later
- Debian/thunderbird—upgrade to 1:140.9.0esr-1~deb11u1 or later
Is CVE-2026-4691 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 |