CVE-2026-2799
Published: 24 February 2026
Summary
CVE-2026-2799 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 5.2th 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
Mandates timely identification, reporting, and patching of flaws like the use-after-free in Firefox and Thunderbird DOM Core & HTML, directly eliminating the vulnerability as recommended by Mozilla.
Provides memory protection mechanisms such as ASLR and non-executable memory that hinder exploitation of use-after-free vulnerabilities by blocking unauthorized memory access and code execution.
Enforces process isolation via browser sandboxing to confine exploitation of the DOM use-after-free to the renderer process, preventing escape to full system compromise.
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Use-after-free in browser DOM parser enables drive-by compromise via malicious websites and direct client-side exploitation for arbitrary code execution without auth or interaction.
NVD Description
Use-after-free in the DOM: Core & HTML component. This vulnerability was fixed in Firefox 148 and Thunderbird 148.
Deeper analysisAI
CVE-2026-2799 is a use-after-free vulnerability (CWE-416) in the DOM Core & HTML component of Mozilla Firefox and Thunderbird. It affects versions prior to Firefox 148 and Thunderbird 148, earning 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 exploitation over the network without authentication or user interaction.
Remote attackers can exploit this vulnerability by tricking users into visiting a malicious website or interacting with crafted content that triggers the use-after-free in the DOM parser. Successful exploitation could allow arbitrary code execution, compromise of the browser process, theft of sensitive data, or full system takeover, as the flaw enables high confidentiality, integrity, and availability impacts.
Mozilla's security advisories (MFSA 2026-13 and MFSA 2026-16) and the associated Bugzilla entry detail the patch applied in Firefox 148 and Thunderbird 148, recommending immediate upgrades to these versions for mitigation. No workarounds are specified beyond updating the affected software.
Details
- CWE(s)