What is CVE-2026-6779?

CVE-2026-6779 is a medium-severity vulnerability in Mozilla Firefox, classified under Improper Input Validation. CVSS score: 5.3/10. Published 2026-04-21.

How severe is CVE-2026-6779?

Medium severity. CVSS v3 base score is 5.3 out of 10.

XSS in Mozilla Firefox

CVE-2026-6779

Other issue in the JavaScript Engine component. This vulnerability was fixed in Firefox 150 and Thunderbird 150.

Vulnerability class: Drupalgeddon 2 (CVE-2018-7600)

EPSS: 0.002 (10.9th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 5.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N.

Affected products

Mozilla Firefox — versions 150
Mozilla Thunderbird — versions 150

Weakness classification (CWE)

CWE-20 — Improper Input Validation
CWE-79 — Cross-site Scripting
CWE-119 — Improper Restriction of Operations within the Bounds of a Memory Buffer

References

security@mozilla.org (Permissions Required)
security@mozilla.org (Vendor Advisory)
security@mozilla.org (Vendor Advisory)

Frequently asked questions

What is CVE-2026-6779?: CVE-2026-6779 is a medium-severity vulnerability in Mozilla Firefox, classified under Improper Input Validation. CVSS score: 5.3/10. Published 2026-04-21.
How severe is CVE-2026-6779?: Medium severity. CVSS v3 base score is 5.3 out of 10.