CVE-2026-6755: Mozilla Firefox

Medium severity, CVSS 6.5. EPSS: 0.2% chance of exploitation in the next 30 days.

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

Affected products

• Mozilla Firefox: before 150.0 (fixed in 150.0)
• Mozilla Thunderbird: before 150.0 (fixed in 150.0)

Published 2026-04-21. Last modified 2026-06-17.