Protection Mechanism Failure in Mozilla Firefox and Firefox for Android - CVE-2026-6755
Published: April 21, 2026
Vulnerability identifier: #VU126678
CSH Severity: Medium
CVSS v4: 5.1 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-6755
CWE-ID: CWE-693
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to bypass a security restriction.
The vulnerability exists due to a mitigation bypass in the DOM: postMessage component when handling postMessage operations. A remote attacker can craft content to bypass a security restriction.
Affected software
Mozilla Firefox
Firefox for Android
Mozilla Thunderbird
Firefox for Android
Mozilla Thunderbird
How to mitigate CVE-2026-6755
Install security update from vendor's website.
Mozilla Firefox - update to 150.0
Firefox for Android - update to 150.0
Mozilla Thunderbird - update to 150.0
Firefox for Android - update to 150.0
Mozilla Thunderbird - update to 150.0