CVE-2026-4721
Published: 24 March 2026
Description
Memory safety bugs present in Firefox ESR 115.33, 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…
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been exploited to run arbitrary code. This vulnerability was fixed in Firefox 149, Firefox ESR 115.34, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.
Mitigating Controls (NIST 800-53 r5)AI
Requires timely remediation of identified flaws, such as applying patches for memory safety bugs in Firefox and Thunderbird to eliminate the vulnerability.
Implements memory protection mechanisms like ASLR and DEP to directly mitigate exploitation of memory corruption from buffer copy without size checks.
Enforces process isolation, such as browser sandboxing, to contain arbitrary code execution within affected processes like Firefox renderers.
Security SummaryAI
CVE-2026-4721 encompasses multiple memory safety bugs classified under CWE-120 (Buffer Copy without Checking Size of Input) affecting Firefox ESR 115.33, 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 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), making it remotely exploitable over the network by unauthenticated attackers with low complexity and no user interaction required. Successful exploitation could grant attackers high-impact control over confidentiality, integrity, and availability, potentially allowing arbitrary code execution within the affected browser or email client processes.
Mozilla has mitigated this issue in updated releases including Firefox 149, Firefox ESR 115.34, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9. Security practitioners should consult Mozilla Security Advisories MFSA2026-20, MFSA2026-21, MFSA2026-22, and MFSA2026-23, along with the linked Bugzilla entries, for patch details and additional technical analysis.
Details
- CWE(s)
Affected Products
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Memory corruption RCE in client applications (browser/email) with AV:N/UI:N directly enables drive-by compromise via malicious web/email content and exploitation for client execution to achieve arbitrary code execution.