Raw vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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-2026-4720 is a critical-severity Classic Buffer Overflow (CWE-120) vulnerability in Mozilla Firefox. Its CVSS base score is 9.8 (Critical).
Operationally, exploitation aligns with the MITRE ATT&CK technique NTDS (T1003.003); ranked at the 35th 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-2026-4720 consists of multiple memory safety bugs, classified under CWE-120, present in Firefox ESR 140.8, Thunderbird ESR 140.8, Firefox 148, and Thunderbird 148. Some of these bugs exhibited evidence of memory corruption, which Mozilla presumes could be exploited to run arbitrary code with sufficient effort. The vulnerability was published on 2026-03-24 and carries a CVSS v3.1 base score of 9.8, reflecting its critical severity.
Attackers can exploit this vulnerability remotely over the network (AV:N) with low attack complexity (AC:L), requiring no privileges (PR:N) or user interaction (UI:N), and without changing scope (S:U). Successful exploitation could result in high impacts to confidentiality, integrity, and availability (C:H/I:H/A:H), enabling potential arbitrary code execution on affected systems.
Mozilla advisories MFSA2026-20, MFSA2026-22, MFSA2026-23, and MFSA2026-24 detail the issues, with fixes available in Firefox 149, Firefox ESR 140.9, Thunderbird 149, and Thunderbird ESR 140.9. Additional technical information is provided in Bugzilla entries for bugs 2004652, 2019372, 2021922, 2022567, and 2022733.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-14855
Vulnerability Data
Memory safety bugs present in Firefox ESR 140.8, Thunderbird ESR 140.8, Firefox 148 and Thunderbird 148. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to…
more
run arbitrary code. This vulnerability was fixed in Firefox 149, 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
Developer testing and analysis can find missing size checks before deployment.
Input validation directly enforces size checks before buffer copies.
Engineering principles require bounds checking and safe buffer handling in 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.
Vulnerability identification processes such as code review or scanning detect classic buffer overflows before exploitation.
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.