CVE-2026-109749 Use-after-free in the JavaScript: WebAssembly component
A use-after-free flaw in the WebAssembly component allows attackers to execute arbitrary code, requiring users to upgrade Firefox and Thunderbird.
- 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-2026-109749?
CVE-2026-109749 is a medium-severity use after free 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
Use-after-free in the JavaScript: WebAssembly component. This vulnerability was fixed in Firefox 158 and Thunderbird 158.
Weakness: CWE-416
Which versions are affected by CVE-2026-109749?
How do I fix CVE-2026-109749?
Upgrade to a fixed version.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2026-109749 being exploited?
There is no known exploitation of CVE-2026-109749 in the wild and no public exploit code.
Sources
Also known as GHSA-ww9p-5q3r-4q4m, UBUNTU-CVE-2026-109749.