CVE-2026-12321 JIT miscompilation in the JavaScript: WebAssembly component

What is CVE-2026-12321?

CVE-2026-12321 is a medium-severity code injection vulnerability in Mozilla Firefox, published on 16 Jun 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 152 and Thunderbird 152.

Weakness: CWE-670

Which versions are affected by CVE-2026-12321?

It affects 2 products.

Products include Mozilla Firefox, Mozilla Thunderbird.

How do I fix CVE-2026-12321?

Upgrade to a fixed version.

Upgrade, and never evaluate templates, expressions or code built from user input. More about Code injection.

Is CVE-2026-12321 being exploited?

There is no known exploitation of CVE-2026-12321 in the wild and no public exploit code.

Other vulnerabilities in Mozilla Firefox

• CVE-2019-11708 Mozilla Firefox and Thunderbird Sandbox Escape Exploited Critical 10.0
• CVE-2010-3765 Mozilla Multiple Products Remote Code Execution Exploited Critical 9.8
• CVE-2022-26486 Mozilla Firefox Use-After-Free Exploited Critical 9.6
• CVE-2022-26485 Mozilla Firefox Use-After-Free Exploited High 8.8
• CVE-2019-11707 Mozilla Firefox and Thunderbird Type Confusion Exploited High 8.8

All Mozilla Firefox vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as GHSA-r946-vv6g-44hh, UBUNTU-CVE-2026-12321.