CVE-2026-2758
Published: 24 February 2026
Summary
CVE-2026-2758 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 37.7th 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-16 (Memory Protection) and SI-2 (Flaw Remediation).
Deeper analysis
CVE-2026-2758 is a use-after-free vulnerability (CWE-416) in the JavaScript Garbage Collector (GC) component, published on 2026-02-24T14:16:24.037. It affects Mozilla Firefox and Thunderbird versions prior to the fixed releases: Firefox 148, Firefox ESR 115.33, 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 due to its potential for severe impact.
A remote attacker can exploit this vulnerability over the network with low complexity, requiring no privileges or user interaction. Exploitation could lead to high confidentiality, integrity, and availability impacts, enabling outcomes such as arbitrary code execution within the affected browser or email client processes.
Mozilla's security advisories (MFSA2026-13, MFSA2026-14, MFSA2026-15, and MFSA2026-16) and Bugzilla entry 2009608 detail the patches applied in the listed versions. Mitigation involves updating to Firefox 148 or later, Firefox ESR 115.33 or later, Firefox ESR 140.8 or later, Thunderbird 148 or later, or Thunderbird 140.8 or later.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-8480
Vulnerability details
Use-after-free in the JavaScript: GC component. This vulnerability was fixed in Firefox 148, Firefox ESR 115.33, 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 RCE in browser/Thunderbird JS GC directly enables client-side exploitation via malicious web content (T1189 Drive-by Compromise) or general client application exploitation (T1203 Exploitation for Client Execution).
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Mandates timely identification, reporting, and correction of flaws such as the use-after-free vulnerability in the JavaScript GC component via patching to fixed versions.
Implements system-level memory protections like ASLR and DEP that directly mitigate exploitation of use-after-free vulnerabilities by restricting unauthorized memory access.
Enables vulnerability scanning to identify affected Firefox and Thunderbird versions prior to exploitation, facilitating prompt 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