Cyber Resilience

CVE-2026-6774

Medium

Published: 21 April 2026

Published
21 April 2026
Modified
22 April 2026
KEV Added
—
Patch
—
CVSS Score v3.1 5.4 CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
EPSS Score 0.0015 4.9th percentile
Risk Priority 35 floored blend · peak EPSS

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, exploitation aligns with the MITRE ATT&CK technique Drive-by Compromise (T1189); ranked at the 4.9th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

The strongest mitigations our analysis identified are NIST 800-53 SI-2 (Flaw Remediation) and SI-3 (Malicious Code Protection).

Deeper analysis

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)

A06:2025 Insecure Design

EU & UK References

Vulnerability details

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

CWE(s)
CWE-693

Related Threats

MITRE ATT&CK Enterprise TechniquesAI

T1189 Drive-by Compromise Initial Access
Adversaries may gain access to a system through a user visiting a website over the normal course of browsing.
attack.mitre.org →
T1203 Exploitation for Client Execution Execution
Adversaries may exploit software vulnerabilities in client applications to execute code.
attack.mitre.org →
T1204.001 Malicious Link Execution
An adversary may rely upon a user clicking a malicious link in order to gain execution.
attack.mitre.org →
Why these techniques?

Browser DOM mitigation bypass directly enables client-side exploitation (T1203) via malicious links or crafted web content (T1204.001, T1189 drive-by).

Confidence: MEDIUM · MITRE ATT&CK Enterprise v19.0

CVEs Like This One

CVE-2026-8969Same product: Mozilla Firefox
CVE-2026-8962Same product: Mozilla Firefox
CVE-2026-6763Same product: Mozilla Firefox
CVE-2026-0877Same product: Mozilla Firefox
CVE-2026-2761Same product: Mozilla Firefox
CVE-2025-1012Same product: Mozilla Firefox
CVE-2025-10528Same product: Mozilla Firefox
CVE-2025-8034Same product: Mozilla Firefox
CVE-2026-2802Same product: Mozilla Firefox
CVE-2025-8032Same product: Mozilla Firefox

Affected Assets

mozilla
firefox
≤ 150.0
mozilla
thunderbird
≤ 150.0

Mitigating Controls

Mitigating Controls (NIST 800-53 r5) AI

SI-2 Flaw Remediation good match
prevent

Directly requires timely application of the vendor patch that eliminates the DOM Security mitigation bypass in Firefox/Thunderbird <150.

SI-3 Malicious Code Protection partial match
preventdetect

Deploys malicious-code detection and blocking mechanisms that can intercept the crafted payloads used to trigger the DOM bypass.

SI-7 Software, Firmware, and Information Integrity partial match
detect

Verifies integrity of browser binaries and components, enabling detection of unauthorized modification or failure of the DOM security enforcement logic.

Hardening callouts derived

Configuration rules from DISA STIG baselines that reduce the attack surface for weaknesses of the type cited by this CVE. Derived transitively via CVE→CWE→STIG over `controls_xwalks` (authoritative rows only).

Oracle Linux 8 (2 rules)
  • V-248524 OL 8 must implement NIST FIPS-validated cryptography for the following: To provision digital signatures, to generate cryptographic hashes, and to protect data requiring data-at-rest protections in accordance with applicable federal laws, Executive Orders, directives, policies, regulations, and standards. via CWE-693
  • V-248525 All OL 8 local disk partitions must implement cryptographic mechanisms to prevent unauthorized disclosure or modification of all information that requires at-rest protection. via CWE-693
Windows 10 (2 rules)
  • V-220865 The Windows Remote Management (WinRM) service must not use Basic authentication. via CWE-693
  • V-220812 Credential Guard must be running on Windows 10 domain-joined systems. via CWE-693
Windows 11 (1 rule)
  • V-253418 The Windows Remote Management (WinRM) service must not use Basic authentication. via CWE-693
Windows Server 2016 (1 rule)
  • V-225012 Windows Server 2016 must be running Credential Guard on domain-joined member servers. via CWE-693
Windows Server 2019 (1 rule)
  • V-205907 Windows Server 2019 must be running Credential Guard on domain-joined member servers. via CWE-693
Windows Server 2022 (1 rule)
  • V-254441 Windows Server 2022 must be running Credential Guard on domain-joined member servers. via CWE-693

References