CVE-2026-109720 JIT miscompilation in the JavaScript: WebAssembly component
A JIT miscompilation in the WebAssembly component allows attackers to execute arbitrary code via crafted web content.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-109720?
CVE-2026-109720 is a high-severity memory corruption vulnerability in Mozilla Firefox, published on 13 Oct 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
JIT miscompilation in the JavaScript: WebAssembly component. This vulnerability was fixed in Firefox 158, Firefox ESR 153.5, Thunderbird 158, and Thunderbird 153.5.
Weakness: CWE-843
Which versions are affected by CVE-2026-109720?
How do I fix CVE-2026-109720?
Upgrade to a fixed version.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-109720 being exploited?
There is no known exploitation of CVE-2026-109720 in the wild and no public exploit code.
Sources
Also known as DEBIAN-CVE-2026-109720, GHSA-5r38-4r4j-9hg3, UBUNTU-CVE-2026-109720.