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Vulnerability · Published Jan 13, 2026 · Assigned by mozilla

CVE-2026-0891Memory safety bugs fixed in Firefox ESR 140.7, Thunderbird ESR 140.7, Firefox 147 and Thunderbird 147

High 8.1

In plain English

A high-severity memory corruption 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)8.1High
Exploit odds (30 days)0.5%top 58.7% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official description

Memory safety bugs present in Firefox ESR 140.6, Thunderbird ESR 140.6, Firefox 146 and Thunderbird 146. 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 147, Firefox ESR 140.7, Thunderbird 147, and Thunderbird 140.7.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
AlmaLinux:10firefox140.7.0-1.el10_1ALSA-2026:2271
AlmaLinux:8firefox140.7.0-1.el8_10.alma.1ALSA-2026:0667
AlmaLinux:9firefox140.7.0-1.el9_7.alma.1ALSA-2026:0694
AlmaLinux:9firefox-x11140.7.0-1.el9_7.alma.1ALSA-2026:0694
AlmaLinux:10thunderbird140.7.0-1.el10_1.alma.1ALSA-2026:2286
AlmaLinux:8thunderbird140.7.0-1.el8_10.alma.1ALSA-2026:2220
AlmaLinux:9thunderbird140.7.0-1.el9_7.alma.1ALSA-2026:0924
Debian:12firefox-esr140.7.0esr-1~deb12u1DEBIAN-CVE-2026-0891
Debian:12firefox-esr140.7.0esr-1~deb12u1DSA-6101-1
Debian:13firefox-esr140.7.0esr-1~deb13u1DEBIAN-CVE-2026-0891
Debian:13firefox-esr140.7.0esr-1~deb13u1DSA-6101-1
Debian:14firefox-esr140.7.0esr-1DEBIAN-CVE-2026-0891
Debian:12thunderbird1:140.7.0esr-1~deb12u1DSA-6103-1
Debian:12thunderbird1:140.7.0esr-1~deb12u1DEBIAN-CVE-2026-0891
Debian:13thunderbird1:140.7.0esr-1~deb13u1DSA-6103-1
Debian:13thunderbird1:140.7.0esr-1~deb13u1DEBIAN-CVE-2026-0891
Debian:14thunderbird1:140.7.0esr-1DEBIAN-CVE-2026-0891
Rocky Linux:8firefox0:140.7.0-1.el8_10RLSA-2026:0667
Rocky Linux:9firefox0:140.7.0-1.el9_7RLSA-2026:0694
Rocky Linux:8thunderbird0:140.7.0-1.el8_10RLSA-2026:2220
Rocky Linux:9thunderbird0:140.7.0-1.el9_7RLSA-2026:0924
Ubuntu:22.04:LTSmozjs102no fix listedUBUNTU-CVE-2026-0891
Ubuntu:24.04:LTSmozjs102no fix listedUBUNTU-CVE-2026-0891
Ubuntu:24.04:LTSmozjs115no fix listedUBUNTU-CVE-2026-0891
Ubuntu:22.04:LTSmozjs78no fix listedUBUNTU-CVE-2026-0891
Ubuntu:22.04:LTSmozjs91no fix listedUBUNTU-CVE-2026-0891
Ubuntu:22.04:LTSthunderbird1:140.7.1+build1-0ubuntu0.22.04.1UBUNTU-CVE-2026-0891

Affected products (as reported)

VendorProductVersions
Mozilla Firefox see references
Mozilla Thunderbird see references

Weakness: CWE-119 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

References