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)

EPSS: 0.002 (8.7th percentile) — read the EPSS interpretation.

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.

Affected products

Mozilla Firefox — versions 150
Mozilla Thunderbird — versions 150

Weakness classification (CWE)

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

References

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