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-2026-4729 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 Security Account Manager (T1003.002); ranked at the 39th 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-2026-4729 is a set of memory safety bugs (classified under CWE-120: Buffer Copy without Checking Size of Input) affecting Firefox version 148 and Thunderbird version 148. These bugs exhibited evidence of memory corruption, which Mozilla presumes could be leveraged with sufficient effort to enable arbitrary code execution. The vulnerability carries a CVSS v3.1 base score of 9.8 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H), indicating critical severity due to its potential for high-impact remote compromise.
Remote attackers can exploit this vulnerability over the network with low complexity, requiring no privileges, user interaction, or special conditions. Successful exploitation could grant attackers high confidentiality, integrity, and availability impacts, potentially allowing full control over the affected browser or email client processes, including execution of arbitrary code within the victim's environment.
Mozilla's security advisories (MFSA 2026-20 and MFSA 2026-23) address the issue, with fixes implemented in Firefox 149 and Thunderbird 149. Security practitioners should prioritize updating affected instances to these versions, as detailed in the referenced Bugzilla entries for bugs 1944033, 1997282, 2009213, 2011412, 2021925, and 2022034.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-14873
Vulnerability Data
Memory safety bugs present in 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 run arbitrary code. This vulnerability was…
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fixed in Firefox 149 and Thunderbird 149.
- 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.
Process isolation confines the effects of a use-after-free within a single address space, reducing cross-process impact.
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.
Lifecycle management includes secure development and maintenance phases that reduce memory-safety defects.
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.