CVE-2026-6755
Published: 21 April 2026
Summary
CVE-2026-6755 is a medium-severity CSRF (CWE-352) vulnerability in Mozilla Firefox. Its CVSS base score is 6.5 (Medium).
Operationally, exploitation aligns with the MITRE ATT&CK technique Application or System Exploitation (T1499.004); ranked at the 5.7th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
Threat & Defense at a Glance
Threat & Defense Details
Likely Mitigating ControlsAI
Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.
Awareness training educates users on avoiding untrusted links and actions that can be exploited via CSRF.
Requiring user re-entry of credentials for sensitive actions prevents automated forgery of requests without active user participation.
Security testing regimens explicitly include checks for missing or ineffective anti-CSRF protections in web applications.
Detects anomalous request patterns consistent with cross-site request forgery.
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Browser postMessage mitigation bypass enables remote exploitation resulting in application DoS (crash/hang), directly matching T1499.004 Application or System Exploitation.
NVD Description
Mitigation bypass in the DOM: postMessage component. This vulnerability was fixed in Firefox 150 and Thunderbird 150.
Deeper analysisAI
CVE-2026-6755 is a mitigation bypass vulnerability in the DOM postMessage component, affecting Mozilla Firefox and Thunderbird. The issue, linked to CWE-352 (Cross-Site Request Forgery), was fixed in Firefox version 150 and Thunderbird version 150. It carries a CVSS v3.1 base score of 6.5 (AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H), indicating medium severity primarily due to high availability impact.
An attacker can exploit this vulnerability over the network with low complexity and low privileges required, without needing user interaction. Exploitation leads to a denial of service, such as application crashes or hangs, while having no impact on confidentiality or integrity.
Mozilla's security advisories MFSA2026-30 and MFSA2026-33 address the vulnerability, recommending updates to Firefox 150 or Thunderbird 150 for mitigation. Further technical details are available in Bugzilla bug 1880429.
Details
- CWE(s)