Vulnerability · Published Mar 24, 2026 · Assigned by mozilla
CVE-2026-4701Use-after-free in the JavaScript Engine component
Critical 9.8
In plain English
A critical-severity use-after-free in Firefox from Mozilla. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 41% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Severity (CVSS 3.1)9.8Critical
Exploit odds (30 days)0.5%top 58.5% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known
Official description
Use-after-free in the JavaScript Engine component. This vulnerability was fixed in Firefox 149, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| AlmaLinux:10 | firefox | 140.9.0-1.el10_1 | ALSA-2026:5931 |
| AlmaLinux:8 | firefox | 140.9.0-1.el8_10.alma.1 | ALSA-2026:5932 |
| AlmaLinux:9 | firefox | 140.9.0-1.el9_7.alma.1 | ALSA-2026:5930 |
| AlmaLinux:9 | firefox-x11 | 140.9.0-1.el9_7.alma.1 | ALSA-2026:5930 |
| AlmaLinux:10 | thunderbird | 140.9.0-1.el10_1.alma.1 | ALSA-2026:6342 |
| AlmaLinux:8 | thunderbird | 140.9.0-1.el8_10.alma.1 | ALSA-2026:6917 |
| AlmaLinux:9 | thunderbird | 140.9.0-1.el9_7.alma.1 | ALSA-2026:6188 |
| Debian:12 | firefox-esr | 140.9.0esr-1~deb12u1 | DSA-6178-1 |
| Debian:12 | firefox-esr | 140.9.0esr-1~deb12u1 | DEBIAN-CVE-2026-4701 |
| Debian:13 | firefox-esr | 140.9.0esr-1~deb13u1 | DEBIAN-CVE-2026-4701 |
| Debian:13 | firefox-esr | 140.9.0esr-1~deb13u1 | DSA-6178-1 |
| Debian:14 | firefox-esr | 140.9.0esr-1 | DEBIAN-CVE-2026-4701 |
| Debian:12 | thunderbird | 1:140.9.0esr-1~deb12u1 | DSA-6179-1 |
| Debian:12 | thunderbird | 1:140.9.0esr-1~deb12u1 | DEBIAN-CVE-2026-4701 |
| Debian:13 | thunderbird | 1:140.9.0esr-1~deb13u1 | DEBIAN-CVE-2026-4701 |
| Debian:13 | thunderbird | 1:140.9.0esr-1~deb13u1 | DSA-6179-1 |
| Debian:14 | thunderbird | 1:140.9.0esr-1 | DEBIAN-CVE-2026-4701 |
| Rocky Linux:10 | firefox | 0:140.9.0-1.el10_1 | RLSA-2026:5931 |
| Rocky Linux:8 | firefox | 0:140.9.0-1.el8_10 | RLSA-2026:5932 |
| Rocky Linux:9 | firefox | 0:140.9.0-1.el9_7 | RLSA-2026:5930 |
| Rocky Linux:10 | thunderbird | 0:140.9.0-1.el10_1 | RLSA-2026:6342 |
| Rocky Linux:8 | thunderbird | 0:140.9.0-1.el8_10 | RLSA-2026:6917 |
| Rocky Linux:9 | thunderbird | 0:140.9.0-1.el9_7 | RLSA-2026:6188 |
| Ubuntu:22.04:LTS | mozjs102 | no fix listed | UBUNTU-CVE-2026-4701 |
| Ubuntu:24.04:LTS | mozjs102 | no fix listed | UBUNTU-CVE-2026-4701 |
| Ubuntu:24.04:LTS | mozjs115 | no fix listed | UBUNTU-CVE-2026-4701 |
| Ubuntu:22.04:LTS | mozjs78 | no fix listed | UBUNTU-CVE-2026-4701 |
| Ubuntu:22.04:LTS | mozjs91 | no fix listed | UBUNTU-CVE-2026-4701 |
| Ubuntu:22.04:LTS | thunderbird | no fix listed | UBUNTU-CVE-2026-4701 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Mozilla | Firefox | see references |
| Mozilla | Thunderbird | see references |
Weakness: CWE-416 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H