What is CVE-2026-4727?

CVE-2026-4727 is a high-severity vulnerability in Mozilla Firefox, classified under Uncontrolled Resource Consumption. CVSS score: 7.5/10. Published 2026-03-24.

How severe is CVE-2026-4727?

High severity. CVSS v3 base score is 7.5 out of 10.

Resource exhaustion in Mozilla Firefox

CVE-2026-4727

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

Vulnerability class: DoS (Denial of Service)

Published 2026-03-24 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

EPSS exploit prediction

EPSS: 0.005 (41.7th percentile), scored 2026-09-29.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 42nd percentile — 41.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.005 · newest: 0.005 · change: -0.000

Affected products

Mozilla Firefox — versions 149
Mozilla Thunderbird — versions 149

Weakness classification (CWE)

CWE-400 — Uncontrolled Resource Consumption

References

bugzilla.mozilla.org/show_bug.cgi (Permissions Required)
www.mozilla.org/security/advisories/mfsa2026-20/ (Vendor Advisory)
www.mozilla.org/security/advisories/mfsa2026-23/ (Vendor Advisory)

Frequently asked questions

What is CVE-2026-4727?: CVE-2026-4727 is a high-severity vulnerability in Mozilla Firefox, classified under Uncontrolled Resource Consumption. CVSS score: 7.5/10. Published 2026-03-24.
How severe is CVE-2026-4727?: High severity. CVSS v3 base score is 7.5 out of 10.