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Vulnerability · Published Mar 24, 2026 · Assigned by mozilla

CVE-2026-4721Memory safety bugs fixed in Firefox ESR 115.34, Firefox ESR 140.9, Thunderbird ESR 140.9, Firefox 149 and Thunderbird 149

Critical 9.8

In plain English

A critical-severity buffer overflow 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 0.4% (higher than 38% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)9.8Critical
Exploit odds (30 days)0.4%top 61.5% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official 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.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
AlmaLinux:10firefox140.9.0-1.el10_1ALSA-2026:5931
AlmaLinux:8firefox140.9.0-1.el8_10.alma.1ALSA-2026:5932
AlmaLinux:9firefox140.9.0-1.el9_7.alma.1ALSA-2026:5930
AlmaLinux:9firefox-x11140.9.0-1.el9_7.alma.1ALSA-2026:5930
AlmaLinux:10thunderbird140.9.0-1.el10_1.alma.1ALSA-2026:6342
AlmaLinux:8thunderbird140.9.0-1.el8_10.alma.1ALSA-2026:6917
AlmaLinux:9thunderbird140.9.0-1.el9_7.alma.1ALSA-2026:6188
Debian:12firefox-esr140.9.0esr-1~deb12u1DSA-6178-1
Debian:12firefox-esr140.9.0esr-1~deb12u1DEBIAN-CVE-2026-4721
Debian:13firefox-esr140.9.0esr-1~deb13u1DEBIAN-CVE-2026-4721
Debian:13firefox-esr140.9.0esr-1~deb13u1DSA-6178-1
Debian:14firefox-esr140.9.0esr-1DEBIAN-CVE-2026-4721
Debian:12thunderbird1:140.9.0esr-1~deb12u1DSA-6179-1
Debian:12thunderbird1:140.9.0esr-1~deb12u1DEBIAN-CVE-2026-4721
Debian:13thunderbird1:140.9.0esr-1~deb13u1DEBIAN-CVE-2026-4721
Debian:13thunderbird1:140.9.0esr-1~deb13u1DSA-6179-1
Debian:14thunderbird1:140.9.0esr-1DEBIAN-CVE-2026-4721
Rocky Linux:10firefox0:140.9.0-1.el10_1RLSA-2026:5931
Rocky Linux:8firefox0:140.9.0-1.el8_10RLSA-2026:5932
Rocky Linux:9firefox0:140.9.0-1.el9_7RLSA-2026:5930
Rocky Linux:10thunderbird0:140.9.0-1.el10_1RLSA-2026:6342
Rocky Linux:8thunderbird0:140.9.0-1.el8_10RLSA-2026:6917
Rocky Linux:9thunderbird0:140.9.0-1.el9_7RLSA-2026:6188
Ubuntu:22.04:LTSmozjs102no fix listedUBUNTU-CVE-2026-4721
Ubuntu:24.04:LTSmozjs102no fix listedUBUNTU-CVE-2026-4721
Ubuntu:24.04:LTSmozjs115no fix listedUBUNTU-CVE-2026-4721
Ubuntu:22.04:LTSmozjs78no fix listedUBUNTU-CVE-2026-4721
Ubuntu:22.04:LTSmozjs91no fix listedUBUNTU-CVE-2026-4721
Ubuntu:22.04:LTSthunderbirdno fix listedUBUNTU-CVE-2026-4721

Affected products (as reported)

VendorProductVersions
Mozilla Firefox see references
Mozilla Thunderbird see references

Weakness: CWE-120, CWE-825 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

References