What’s Vulnerable › Vulnerabilities

CVE-2026-6755: Mitigation bypass in the DOM: postMessage component

• Severity: medium (CVSS 6.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-04-21 · updated 2026-10-26
• Weakness: CWE-352

Description

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

How to fix

Upgrade to a fixed version: Mozilla Firefox 150.0; Mozilla Thunderbird 150.0. Check the vendor advisory for mitigations.

References

• https://bugzilla.mozilla.org/show_bug.cgi?id=1880429
• https://www.mozilla.org/security/advisories/mfsa2026-30/
• https://www.mozilla.org/security/advisories/mfsa2026-33/

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