Raw vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:HCVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.
Summary
CVE-2026-4687 is a high-severity Improper Check for Unusual or Exceptional Conditions (CWE-754) vulnerability in Mozilla Firefox. Its CVSS base score is 8.6 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Data Obfuscation (T1001); ranked at the 44th 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-4 (Information Flow Enforcement) and SA-11 (Developer Testing and Evaluation) — 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-2026-4687 is a sandbox escape vulnerability caused by incorrect boundary conditions in the Telemetry component of Mozilla Firefox and Thunderbird. Published on 2026-03-24, it carries a CVSS v3.1 base score of 8.6 (AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H) and maps to CWE-754 (Improper Check for Unusual or Exceptional Conditions) and CWE-120 (Buffer Copy without Checking Size of Input). The flaw affects Firefox and Thunderbird versions prior to the patched releases.
Remote attackers can exploit this vulnerability over the network with low attack complexity, requiring no privileges, user interaction, or authentication. Exploitation results in a change of scope from the sandboxed context, enabling high-impact availability disruption such as application crashes or denial of service, while confidentiality and integrity remain unaffected.
Mozilla fixed the vulnerability in Firefox 149, Firefox ESR 115.34, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9. Security advisories MFSA2026-20, MFSA2026-21, MFSA2026-22, and MFSA2026-23, along with Bugzilla entry 2016368, provide further details on the patches and recommend immediate updates to mitigate the risk.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-14798
Vulnerability Data
Sandbox escape due to incorrect boundary conditions in the Telemetry component. This vulnerability was fixed in Firefox 149, Firefox ESR 115.34, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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V5.2.1
Mitigating Controls (NIST 800-53 r5) AI
Information flow enforcement directly stops trusted and untrusted data from being combined by applying rules that govern allowable data movements and combinations.
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.
Associating explicit security attributes with data objects enables enforcement mechanisms that keep trust levels from being mixed inside structures.
Security engineering principles include structured handling of edge cases and exceptions during design.
Memory protection limits the impact of an overflow once it occurs.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Documented data-flow representations make trust boundaries explicit and help surface mixing of trusted/untrusted data.
Vulnerability identification processes such as code review or scanning detect classic buffer overflows before exploitation.
Logical segmentation and access controls enforce separation between trust domains, reducing the chance of co-mingled data structures.
Routine patching replaces vulnerable code containing unchecked buffer copies with corrected versions.
Secure development practices directly enforce bounds checking and input validation that prevent classic buffer overflows.
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.
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.