CVE-2026-4727 Denial-of-service in the Libraries component in NSS

What is CVE-2026-4727?

CVE-2026-4727 is a high-severity denial of service vulnerability in Mozilla Firefox, published on 24 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

Denial-of-service in the Libraries component in NSS. This vulnerability was fixed in Firefox 149 and Thunderbird 149.

Weakness: CWE-400

Which versions are affected by CVE-2026-4727?

It affects 2 products.

Products include Mozilla Firefox, Mozilla Thunderbird.

How do I fix CVE-2026-4727?

Upgrade to a fixed version.

Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.

Is CVE-2026-4727 being exploited?

There is no known exploitation of CVE-2026-4727 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-f58q-fr7j-32m6, UBUNTU-CVE-2026-4727.