CVE-2026-4701
published 2026-03-24CVE-2026-4701: 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.
PriorityP352critical9.8CVSS 3.1
AVNACLPRNUINSUCHIHAH
EPSS
0.46%
37.4th percentile
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
10 ranges
| Vendor | Product | Version range | Fixed in |
|---|---|---|---|
| debian | firefox | < firefox 149.0-1 (sid) | firefox 149.0-1 (sid) |
| debian | firefox-esr | < firefox 149.0-1 (sid) | firefox 149.0-1 (sid) |
| debian | thunderbird | < firefox 149.0-1 (sid) | firefox 149.0-1 (sid) |
| mozilla | firefox | < 140.9.0 | 140.9.0 |
| mozilla | firefox | < 149.0 | 149.0 |
| mozilla | firefox | — | — |
| mozilla | thunderbird | >= 0 < 1:140.9.0esr-1~deb11u1 | 1:140.9.0esr-1~deb11u1 |
| mozilla | thunderbird | >= 0 < 1:140.9.0esr-1~deb12u1 | 1:140.9.0esr-1~deb12u1 |
| mozilla | thunderbird | >= 0 < 1:140.9.0esr-1~deb13u1 | 1:140.9.0esr-1~deb13u1 |
| mozilla | thunderbird | >= 0 < 1:140.9.0esr-1 | 1:140.9.0esr-1 |
CVSS provenance
nvdv3.19.8CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
osv9.8CRITICAL
vendor_debian9.8CRITICAL
vendor_redhat9.8CRITICAL
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VulDB
Mozilla Firefox up to 148 JavaScript Engine use after free (Nessus ID 303809 / WID-SEC-2026-0850)
vuldb·2026-04-16·CVSS 9.8
CVE-2026-4701 [CRITICAL] Mozilla Firefox up to 148 JavaScript Engine use after free (Nessus ID 303809 / WID-SEC-2026-0850)
A vulnerability, which was classified as critical, was found in Mozilla Firefox up to 148. This impacts an unknown function of the component JavaScript Engine. The manipulation results in use after free.
This vulnerability is identified as CVE-2026-4701. The attack can be executed remotely. There is not any exploit available.
You should upgrade the affected component.
OSV
CVE-2026-4701: Use-after-free in the JavaScript Engine component
osv·2026-03-24·CVSS 9.8
CVE-2026-4701 [CRITICAL] CVE-2026-4701: Use-after-free in the JavaScript Engine component
Use-after-free in the JavaScript Engine component. This vulnerability affects Firefox < 149, Firefox ESR < 140.9, Thunderbird < 149, and Thunderbird < 140.9.
GHSA
GHSA-hxpv-3x38-h8v5: Use-after-free in the JavaScript Engine component
ghsa_unreviewed·2026-03-24
CVE-2026-4701 [CRITICAL] CWE-416 GHSA-hxpv-3x38-h8v5: Use-after-free in the JavaScript Engine component
Use-after-free in the JavaScript Engine component. This vulnerability affects Firefox < 149 and Firefox ESR < 140.9.
Red Hat
firefox: thunderbird: Use-after-free in the JavaScript Engine component
vendor_redhat·2026-03-24·CVSS 9.8
CVE-2026-4701 [CRITICAL] CWE-825 firefox: thunderbird: Use-after-free in the JavaScript Engine component
firefox: thunderbird: Use-after-free in the JavaScript Engine component
Use-after-free in the JavaScript Engine component. This vulnerability affects Firefox < 149, Firefox ESR < 140.9, Thunderbird < 149, and Thunderbird < 140.9.
A flaw was found in Firefox and Thunderbird. The Mozilla Foundation's Security Advisory describes the following issue:
Use-after-free in the JavaScript Engine component
Statement: Red Hat Product Security rates the severity of this flaw as determined by the Mozilla Foundation Security Advisory.
Package: rhel10/firefox-flatpak (Red Hat Enterprise Linux 10) - Affected
Package: rhel10/thunderbird-flatpak (Red Hat Enterprise Linux 10) - Affected
Package: firefox (Red Hat Enterprise Linux 6) - Out of support scope
Package: thunderbird (Red Hat Enterprise Linux 6
Debian
CVE-2026-4701: firefox - Use-after-free in the JavaScript Engine component. This vulnerability affects Fi...
vendor_debian·2026·CVSS 9.8
CVE-2026-4701 [CRITICAL] CVE-2026-4701: firefox - Use-after-free in the JavaScript Engine component. This vulnerability affects Fi...
Use-after-free in the JavaScript Engine component. This vulnerability affects Firefox < 149, Firefox ESR < 140.9, Thunderbird < 149, and Thunderbird < 140.9.
Scope: local
sid: resolved (fixed in 149.0-1)
Mozilla
Mozilla Foundation Security Advisory 2026-23: CVE-2026-4701
vendor_mozilla·CVSS 9.8
CVE-2026-4701 [CRITICAL] Mozilla Foundation Security Advisory 2026-23: CVE-2026-4701
Mozilla Foundation Security Advisory 2026-23
CVE: CVE-2026-4701
Product: Thunderbird
Impact: high
Fixed in: Thunderbird 149
Mozilla
Mozilla Foundation Security Advisory 2026-22: CVE-2026-4701
vendor_mozilla·CVSS 9.8
CVE-2026-4701 [CRITICAL] Mozilla Foundation Security Advisory 2026-22: CVE-2026-4701
Mozilla Foundation Security Advisory 2026-22
CVE: CVE-2026-4701
Product: Firefox ESR
Impact: high
Fixed in: Firefox ESR 140.9
Mozilla
Mozilla Foundation Security Advisory 2026-20: CVE-2026-4701
vendor_mozilla·CVSS 9.8
CVE-2026-4701 [CRITICAL] Mozilla Foundation Security Advisory 2026-20: CVE-2026-4701
Mozilla Foundation Security Advisory 2026-20
CVE: CVE-2026-4701
Product: Firefox
Impact: high
Fixed in: Firefox 149
Mozilla
Mozilla Foundation Security Advisory 2026-24: CVE-2026-4701
vendor_mozilla·CVSS 9.8
CVE-2026-4701 [CRITICAL] Mozilla Foundation Security Advisory 2026-24: CVE-2026-4701
Mozilla Foundation Security Advisory 2026-24
CVE: CVE-2026-4701
Product: Thunderbird
Impact: high
Fixed in: Thunderbird 140.9
No detection rules found.
No public exploits indexed.
Wiz
CVE-2026-4701 Impact, Exploitability, and Mitigation Steps | Wiz
blogs_wiz·CVSS 7.5
CVE-2026-4701 [HIGH] CVE-2026-4701 Impact, Exploitability, and Mitigation Steps | Wiz
## CVE-2026-4701 :
NixOS vulnerability analysis and mitigation
Use-after-free in the JavaScript Engine component. This vulnerability affects Firefox < 149, Firefox ESR < 140.9, Thunderbird < 149, and Thunderbird < 140.9.
Source : NVD
## 9.8
Score
Published March 24, 2026
Severity CRITICAL
CNA Score 9.8
Affected Technologies
NixOS
Mozilla Firefox
Has Public Exploit No
Has CISA KEV Exploit No
CISA KEV Release Date N/A
CISA KEV Due Date N/A
Exploitation Probability Percentile (EPSS) 6
Exploitation Probability (EPSS) N/A
Affected packages and libraries
rhel10::firefox-flatpak.src
rhel10::thunderbird-flatpak
Sources
AlmaLinux 8 Severity HIGH Has Fix Added at: Mar 31, 2026
AlmaLinux 9 Severity HIGH Has Fix Added at: Mar 31, 2026
Chainguard Has Fix Added at: Mar 29, 2026
Bugzilla
CVE-2026-4701 firefox: thunderbird: Use-after-free in the JavaScript Engine component
bugzilla·2026-03-24·CVSS 9.8
CVE-2026-4701 [CRITICAL] CVE-2026-4701 firefox: thunderbird: Use-after-free in the JavaScript Engine component
CVE-2026-4701 firefox: thunderbird: Use-after-free in the JavaScript Engine component
Use-after-free in the JavaScript Engine component. This vulnerability affects Firefox < 149 and Firefox ESR < 140.9.
Discussion:
This issue has been addressed in the following products:
Red Hat Enterprise Linux 10
Via RHSA-2026:5931 https://access.redhat.com/errata/RHSA-2026:5931
---
This issue has been addressed in the following products:
Red Hat Enterprise Linux 9
Via RHSA-2026:5930 https://access.redhat.com/errata/RHSA-2026:5930
---
This issue has been addressed in the following products:
Red Hat Enterprise Linux 8
Via RHSA-2026:5932 https://access.redhat.com/errata/RHSA-2026:5932
---
This issue has been addressed in the following products:
Red Hat Enterprise Linux 9
Via RHSA-2026:6188
2026-03-24
Published