CVE-2026-2786
Published: 24 February 2026
Summary
CVE-2026-2786 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 23.2th 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 RA-5 (Vulnerability Monitoring and Scanning).
Deeper analysis
CVE-2026-2786 is a use-after-free vulnerability (CWE-416) in the JavaScript Engine component of Mozilla products. It affects Firefox, Firefox ESR, and Thunderbird, with fixes applied in Firefox 148, Firefox ESR 140.8, Thunderbird 148, and Thunderbird 140.8.
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), marking it as critical. Remote attackers require no privileges or user interaction and can exploit it over the network with low attack complexity. Successful exploitation enables high-impact compromise of confidentiality, integrity, and availability, such as arbitrary code execution within the browser context.
Mozilla's security advisories (MFSA 2026-13, MFSA 2026-15, MFSA 2026-16, and MFSA 2026-17), along with Bugzilla entry 2013612, document the issue and recommend updating to the patched versions for mitigation.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-8507
Vulnerability details
Use-after-free in the JavaScript Engine component. This vulnerability was fixed in Firefox 148, Firefox ESR 140.8, Thunderbird 148, and Thunderbird 140.8.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Use-after-free in browser JS engine enables remote arbitrary code execution with no privileges or interaction, directly facilitating drive-by compromise (T1189) and exploitation for client execution (T1203) via malicious web content or email rendering.
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Directly requires timely identification, reporting, and correction of the use-after-free flaw via patching to the fixed Firefox and Thunderbird versions.
Implements memory protections like ASLR and DEP that mitigate exploitation of the use-after-free vulnerability in the JavaScript engine.
Enables vulnerability scanning to identify systems affected by CVE-2026-2786 and trigger remediation.
Hardening callouts derived
Configuration rules from DISA STIG baselines that reduce the attack surface for weaknesses of the type cited by this CVE. Derived transitively via CVE→CWE→STIG over `controls_xwalks` (authoritative rows only).
Oracle Linux 8 (1 rule)
- V-248592 OL 8 must clear memory when it is freed to prevent use-after-free attacks. via CWE-416
RHEL 8 (1 rule)
- V-230279 RHEL 8 must clear memory when it is freed to prevent use-after-free attacks. via CWE-416
RHEL 9 (1 rule)
- V-257794 RHEL 9 must clear memory when it is freed to prevent use-after-free attacks. via CWE-416