CVE-2026-6774
Mozilla Firefox ≤ 150.0
Raw vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:NCVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.
Summary
CVE-2026-6774 is a medium-severity Protection Mechanism Failure (CWE-693) vulnerability in Mozilla Firefox. Its CVSS base score is 5.4 (Medium).
Operationally, ranked at the 16th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified map to AC-3 (Access Enforcement) and AC-4 (Information Flow Enforcement) — see the control section below for these in your framework.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
CVE-2026-6774 is a mitigation bypass vulnerability in the DOM Security component of Mozilla Firefox and Thunderbird. It affects versions prior to Firefox 150 and Thunderbird 150, where attackers can circumvent security protections in the Document Object Model handling. The issue is classified under CWE-693 (Protection Mechanism Failure) with a CVSS v3.1 base score of 5.4 (AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N), indicating medium severity due to network accessibility, low attack complexity, and limited impact on confidentiality and integrity.
Exploitation requires a low-privileged attacker (PR:L) with network access to deliver a malicious payload, combined with user interaction (UI:R), such as clicking a link or engaging with crafted content. Successful exploitation changes the scope (S:C) to allow limited disclosure of sensitive information (C:L) or modification of data (I:L) within the browser or email client context, bypassing intended DOM security mitigations without impacting availability.
Mozilla's security advisories (MFSA 2026-30 and MFSA 2026-33) confirm the fix in Firefox 150 and Thunderbird 150, recommending immediate upgrades to patched versions. Additional details are available in Bugzilla ticket 2016915.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-24115
Vulnerability Data
Mitigation bypass in the DOM: Security component. This vulnerability was fixed in Firefox 150 and Thunderbird 150.
- CWE(s)
Related Threats
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
AC-3 directly requires enforcement of access authorizations via the protection mechanism itself.
AC-4 mandates use of information flow enforcement mechanisms to control data movement.
SC-2 requires separation of user and system functionality as a protection mechanism.
SC-28 requires protection mechanisms for information at rest.
SC-3 requires isolation of security functions from non-security functions.
SC-7 requires boundary protection mechanisms to monitor and control external communications.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Systematic verification that security mechanisms operate according to defined standards reduces the likelihood that protection mechanisms are bypassed or disabled.
A.8.26 only requires that security requirements (including protection mechanisms) be identified and specified during development or acquisition; it does not itself mandate, implement, or enforce the mechanisms that would remove CWE-693 instances from the product.
A.8.28 mandates secure coding practices, principles, standards, design, peer review, defect removal, prohibition of insecure techniques (e.g. hard-coded passwords), and evaluation of common errors before deployment, which directly removes many instances of missing or incorrectly used protection mechanisms from first-party code; the bounded remainder is third-party components and post-deployment issues handled by other clauses (8.8, 8.29).
Hardening callouts derived
DISA STIG baselines are authored against specific weaknesses. Where this CVE cites a broad weakness class, the mapping is not asserted at that abstraction (owner ruling, 2026-09-25: grade only at Base and below), so no rule is shown here rather than a rule shown against the wrong grain.