What is CVE-2026-6774?

CVE-2026-6774 is a medium-severity vulnerability in Mozilla Firefox, classified under Protection Mechanism Failure. CVSS score: 5.4/10. Published 2026-04-21.

How severe is CVE-2026-6774?

Medium severity. CVSS v3 base score is 5.4 out of 10.

Vulnerability in Mozilla Firefox

CVE-2026-6774

Mitigation bypass in the DOM: Security component. This vulnerability was fixed in Firefox 150 and Thunderbird 150.

Published 2026-04-21 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 5.4 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N.

EPSS exploit prediction

EPSS: 0.003 (15.7th percentile), scored 2026-09-30.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 16th percentile — 15.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.002 · newest: 0.003 · change: +0.001

Affected products

Mozilla Firefox — versions 150
Mozilla Thunderbird — versions 150

Weakness classification (CWE)

CWE-693 — Protection Mechanism Failure

References

bugzilla.mozilla.org/show_bug.cgi (Permissions Required)
www.mozilla.org/security/advisories/mfsa2026-30/ (Vendor Advisory)
www.mozilla.org/security/advisories/mfsa2026-33/ (Vendor Advisory)

Frequently asked questions

What is CVE-2026-6774?: CVE-2026-6774 is a medium-severity vulnerability in Mozilla Firefox, classified under Protection Mechanism Failure. CVSS score: 5.4/10. Published 2026-04-21.
How severe is CVE-2026-6774?: Medium severity. CVSS v3 base score is 5.4 out of 10.