Vulnerability · Published Oct 13, 2026 · Assigned by mozilla
CVE-2026-109721Incorrect boundary conditions in the JavaScript Engine: JIT component
Medium 5.4
In plain English
A medium-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 0.3% (higher than 20% of all known vulnerabilities). Ready-made attack tooling exists: public proof-of-concept code. Fixed versions are available - upgrade the affected package.
Severity (CVSS 3.1)5.4Medium
Exploit odds (30 days)0.3%top 79.7% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack tooling1Public PoC
Official description
Incorrect boundary conditions in the JavaScript Engine: JIT component. This vulnerability was fixed in Firefox 158, Firefox ESR 153.5, Thunderbird 158, and Thunderbird 153.5.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| AlmaLinux:10 | firefox | 153.5.0-1.el10_2 | ALSA-2026:89758 |
| AlmaLinux:8 | firefox | 153.5.0-1.el8_10 | ALSA-2026:89756 |
| AlmaLinux:9 | firefox | 153.5.0-1.el9_8 | ALSA-2026:89757 |
| AlmaLinux:9 | firefox-x11 | 153.5.0-1.el9_8 | ALSA-2026:89757 |
| AlmaLinux:9 | thunderbird | 153.5.0-1.el9_8.alma.1 | ALSA-2026:93443 |
| Debian:12 | firefox-esr | 153.5.0esr-1~deb12u1 | DEBIAN-CVE-2026-109721 |
| Debian:13 | firefox-esr | 153.5.0esr-1~deb13u1 | DEBIAN-CVE-2026-109721 |
| Debian:14 | firefox-esr | 153.5.0esr-1 | DEBIAN-CVE-2026-109721 |
| Debian:12 | thunderbird | 1:153.5.1esr-1~deb12u1 | DEBIAN-CVE-2026-109721 |
| Debian:13 | thunderbird | 1:153.5.1esr-1~deb13u1 | DEBIAN-CVE-2026-109721 |
| Debian:14 | thunderbird | 1:153.5.0esr-1 | DEBIAN-CVE-2026-109721 |
| Rocky Linux:10 | firefox | 0:153.5.0-1.el10_2 | RLSA-2026:89758 |
| Rocky Linux:8 | firefox | 0:153.5.0-1.el8_10 | RLSA-2026:89756 |
| Rocky Linux:9 | firefox | 0:153.5.0-1.el9_8 | RLSA-2026:89757 |
| Rocky Linux:9 | thunderbird | 0:153.5.0-1.el9_8 | RLSA-2026:93443 |
| Ubuntu:22.04:LTS | mozjs102 | no fix listed | UBUNTU-CVE-2026-109721 |
| Ubuntu:24.04:LTS | mozjs102 | no fix listed | UBUNTU-CVE-2026-109721 |
| Ubuntu:24.04:LTS | mozjs115 | no fix listed | UBUNTU-CVE-2026-109721 |
| Ubuntu:22.04:LTS | mozjs78 | no fix listed | UBUNTU-CVE-2026-109721 |
| Ubuntu:22.04:LTS | mozjs91 | no fix listed | UBUNTU-CVE-2026-109721 |
| Ubuntu:22.04:LTS | thunderbird | no fix listed | UBUNTU-CVE-2026-109721 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Mozilla | Firefox | see references |
| Mozilla | Thunderbird | see references |
Weakness: CWE-119 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N