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Vulnerability · Published May 12, 2026 · Assigned by mozilla

CVE-2026-8391Other issue in the JavaScript Engine component

Medium 5.3

In plain English

A medium-severity improper input validation 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 0.3% (higher than 23% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)5.3Medium
Exploit odds (30 days)0.3%top 77.4% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official description

Other issue in the JavaScript Engine component. This vulnerability was fixed in Firefox 150.0.3, Firefox ESR 115.36, Firefox ESR 140.11, and Thunderbird 140.11.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
AlmaLinux:10firefox140.11.0-1.el10_2ALSA-2026:21380
AlmaLinux:8firefox140.11.0-1.el8_10.alma.1ALSA-2026:21382
AlmaLinux:9firefox140.11.0-1.el9_8.alma.1ALSA-2026:21378
AlmaLinux:9firefox-x11140.11.0-1.el9_8.alma.1ALSA-2026:21378
AlmaLinux:10thunderbird140.11.0-1.el10_2.alma.1ALSA-2026:22325
AlmaLinux:8thunderbird140.11.0-1.el8_10.alma.1ALSA-2026:22643
AlmaLinux:9thunderbird140.11.0-1.el9_8.alma.1ALSA-2026:21381
Debian:12firefox-esr140.11.0esr-1~deb12u1DEBIAN-CVE-2026-8391
Debian:13firefox-esr140.11.0esr-1~deb13u1DEBIAN-CVE-2026-8391
Debian:14firefox-esr140.11.0esr-1DEBIAN-CVE-2026-8391
Debian:12thunderbird1:140.11.0esr-1~deb12u1DEBIAN-CVE-2026-8391
Debian:13thunderbird1:140.11.0esr-1~deb13u1DEBIAN-CVE-2026-8391
Debian:14thunderbird1:140.11.0esr-1DEBIAN-CVE-2026-8391
Rocky Linux:10firefox0:140.11.0-1.el10_2RLSA-2026:21380
Rocky Linux:8firefox0:140.11.0-1.el8_10RLSA-2026:21382
Rocky Linux:9firefox0:140.11.0-1.el9_8RLSA-2026:21378
Rocky Linux:10thunderbird0:140.11.0-1.el10_2RLSA-2026:22325
Rocky Linux:8thunderbird0:140.11.0-1.el8_10RLSA-2026:22643
Rocky Linux:9thunderbird0:140.11.0-1.el9_8RLSA-2026:21381
Ubuntu:22.04:LTSmozjs102no fix listedUBUNTU-CVE-2026-8391
Ubuntu:24.04:LTSmozjs102no fix listedUBUNTU-CVE-2026-8391
Ubuntu:24.04:LTSmozjs115no fix listedUBUNTU-CVE-2026-8391
Ubuntu:22.04:LTSmozjs78no fix listedUBUNTU-CVE-2026-8391
Ubuntu:22.04:LTSmozjs91no fix listedUBUNTU-CVE-2026-8391
Ubuntu:22.04:LTSthunderbirdno fix listedUBUNTU-CVE-2026-8391

Affected products (as reported)

VendorProductVersions
Mozilla Firefox see references
Mozilla Thunderbird see references

Weakness: CWE-20, CWE-79, CWE-119, CWE-475 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

References