CVE-2026-4696
Published: 24 March 2026
Summary
CVE-2026-4696 is a critical-severity Use After Free (CWE-416) vulnerability in Mozilla Firefox. Its CVSS base score is 9.8 (Critical).
Operationally, exploitation aligns with the MITRE ATT&CK technique Drive-by Compromise (T1189); ranked at the 8.5th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified are NIST 800-53 SI-2 (Flaw Remediation) and SC-39 (Process Isolation).
Threat & Defense at a Glance
Threat & Defense Details
Mitigating Controls (NIST 800-53 r5)AI
Directly mandates timely patching of known software flaws like this use-after-free vulnerability in Firefox and Thunderbird.
Implements memory safeguards such as ASLR and DEP that mitigate exploitation of use-after-free errors in the browser's rendering engine.
Enforces process isolation via browser sandboxing to limit the impact and potential code execution from the layout component vulnerability.
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Use-after-free RCE in browser rendering engine (no auth/interaction) directly enables drive-by delivery of malicious content and client-side exploitation for arbitrary code execution.
NVD Description
Use-after-free in the Layout: Text and Fonts component. This vulnerability was fixed in Firefox 149, Firefox ESR 115.34, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.
Deeper analysisAI
CVE-2026-4696 is a use-after-free vulnerability (CWE-416) in the Layout: Text and Fonts component of Mozilla Firefox and Thunderbird. It affects versions of Firefox prior to 149, Firefox ESR prior to 115.34 and 140.9, and Thunderbird prior to 149 and 140.9. The issue was publicly disclosed on 2026-03-24 and carries a CVSS v3.1 base score of 9.8, indicating critical severity due to its potential for high impact.
Remote attackers can exploit this vulnerability over the network with low complexity, requiring no privileges or user interaction. Successful exploitation could result in high impacts to confidentiality, integrity, and availability, potentially allowing arbitrary code execution within the browser's rendering engine.
Mozilla addressed the vulnerability in the specified fixed releases: Firefox 149, Firefox ESR 115.34 and 140.9, Thunderbird 149, and Thunderbird 140.9. Detailed information is available in Mozilla's security advisories MFSA 2026-20 through MFSA 2026-23 and Bugzilla entry 2020190. Security practitioners should prioritize updating affected products to mitigate exposure.
Details
- CWE(s)