What is CVE-2026-6755?

CVE-2026-6755 is a medium-severity vulnerability in Mozilla Firefox, classified under Cross-Site Request Forgery (CSRF). CVSS score: 6.5/10. Published 2026-04-21.

How severe is CVE-2026-6755?

Medium severity. CVSS v3 base score is 6.5 out of 10.

CSRF in Mozilla Firefox

CVE-2026-6755

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

Vulnerability class: CSRF (Cross-Site Request Forgery)

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

CVSS v3 metric

CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H.

EPSS exploit prediction

EPSS: 0.002 (14.5th percentile), scored 2026-09-30.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 14th percentile — 14.5% 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: 0.002 · change: +0.001

Affected products

Mozilla Firefox — versions 150
Mozilla Thunderbird — versions 150

Weakness classification (CWE)

CWE-352 — Cross-Site Request Forgery (CSRF)

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-2026-6755?: CVE-2026-6755 is a medium-severity vulnerability in Mozilla Firefox, classified under Cross-Site Request Forgery (CSRF). CVSS score: 6.5/10. Published 2026-04-21.
How severe is CVE-2026-6755?: Medium severity. CVSS v3 base score is 6.5 out of 10.