CVE-2026-84118 Use-after-free in the JavaScript: GC component
A use-after-free flaw in the JavaScript garbage collector allows attackers to execute arbitrary code via malicious 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-2026-84118?
CVE-2026-84118 is a medium-severity use after free vulnerability in Mozilla Firefox, published on 1 Sep 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: GC component. This vulnerability was fixed in Firefox 155, Firefox ESR 153.2, Thunderbird 155, and Thunderbird 153.2.
Weakness: CWE-416
Which versions are affected by CVE-2026-84118?
It affects 2 products.
Products include Mozilla Firefox, Mozilla Thunderbird.
How do I fix CVE-2026-84118?
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-2026-84118 being exploited?
There is no known exploitation of CVE-2026-84118 in the wild and no public exploit code.
Public exploit code: 1 proofs of concept on GitHub.
Other vulnerabilities in Mozilla Firefox
Sources
Also known as GHSA-26h4-6rvj-cph2, UBUNTU-CVE-2026-84118.