CVE-2026-6766 Incorrect boundary conditions in the Libraries component in NSS

What is CVE-2026-6766?

CVE-2026-6766 is a high-severity vulnerability in Mozilla Firefox, published on 21 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

Incorrect boundary conditions in the Libraries component in NSS. This vulnerability was fixed in Firefox 150, Firefox ESR 140.10, Thunderbird 150, and Thunderbird 140.10.

Weakness: CWE-754

Which versions are affected by CVE-2026-6766?

It affects 2 products.

Products include Mozilla Firefox, Mozilla Thunderbird.

How do I fix CVE-2026-6766?

Upgrade to a fixed version.

Is CVE-2026-6766 being exploited?

There is no known exploitation of CVE-2026-6766 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-2026-6766, ECHO-b379-2860-2350, GHSA-q6qg-6fmg-jjcv, UBUNTU-CVE-2026-6766.