CVE-2026-8391 Other issue in the JavaScript Engine component

What is CVE-2026-8391?

CVE-2026-8391 is a medium-severity cross-site scripting vulnerability in Mozilla Firefox, published on 12 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

Other issue in the JavaScript Engine component. This vulnerability was fixed in Firefox 150.0.3, Firefox ESR 115.36, Firefox ESR 140.11, and Thunderbird 140.11.

Weakness: CWE-79, CWE-475, CWE-20, CWE-119

Which versions are affected by CVE-2026-8391?

It affects 1 product.

Products include Mozilla Firefox.

How do I fix CVE-2026-8391?

Upgrade to a fixed version.

Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.

Is CVE-2026-8391 being exploited?

There is no known exploitation of CVE-2026-8391 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 DEBIAN-CVE-2026-8391, GHSA-93pv-vhrf-wv64, UBUNTU-CVE-2026-8391.