CVE-2026-6766
Mozilla Firefox ≤ 140.10.0
Raw vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/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-2026-6766 is a high-severity Improper Check for Unusual or Exceptional Conditions (CWE-754) vulnerability in Mozilla Firefox. Its CVSS base score is 7.5 (High).
Operationally, ranked at the 36th 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 SA-11 (Developer Testing and Evaluation) and SI-10 (Information Input Validation) — 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-2026-6766 is a vulnerability involving incorrect boundary conditions in the Libraries component of NSS (Network Security Services). NSS is a set of libraries used for cryptographic and security functions in Mozilla products, specifically affecting Firefox, Firefox ESR, and Thunderbird prior to their respective patched versions.
The vulnerability has a CVSS v3.1 base score of 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N), indicating it can be exploited remotely by unauthenticated attackers with low complexity and no user interaction required. Successful exploitation allows attackers to achieve high-impact confidentiality violations, such as disclosing sensitive information processed or stored by affected applications.
Mozilla security advisories (MFSA 2026-30 through 2026-34) and the associated Bugzilla entry detail the fix applied in Firefox 150, Firefox ESR 140.10, Thunderbird 150, and Thunderbird 140.10. Security practitioners should ensure these updates are applied to mitigate the issue, as classified under CWE-754 (Improper Check for Unusual or Exceptional Conditions).
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-24107
Vulnerability Data
Incorrect boundary conditions in the Libraries component in NSS. This vulnerability was fixed in Firefox 150, Firefox ESR 140.10, Thunderbird 150, and Thunderbird 140.10.
- CWE(s)
Related Threats
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Developer testing and evaluation explicitly exercises unusual conditions to find missing or incorrect checks.
Input validation directly requires checking for unexpected or malformed conditions before they propagate.
Security engineering principles include structured handling of edge cases and exceptions during design.
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.
Logging can record unhandled exceptions but does not prevent the weakness itself.
Monitoring may detect symptoms of unhandled conditions but does not eliminate the root weakness.
Secure development life cycle mandates exception handling and input validation that directly prevent missing checks for unusual conditions.
Application security requirements explicitly call for handling of exceptional conditions and error paths.
A.8.27 mandates security-by-design principles (fail securely, least privilege, distrust external input, security-oriented design reviews) that reach some but not most CWE-754 cases; many exceptional-condition checks live in low-level code paths outside architecture-level engineering.
Secure coding standards directly mandate proper checks for exceptional and unusual conditions.
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.
- No fine-grained STIG row for CWE-754, a class-level weakness. Rules are authored against its narrower children: CWE-354.