CVE-2026-6754
Published: 21 April 2026
Summary
CVE-2026-6754 is a high-severity Use After Free (CWE-416) vulnerability in Mozilla Firefox. Its CVSS base score is 7.5 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Application or System Exploitation (T1499.004); ranked at the 30.7th 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-2 (Flaw Remediation) and RA-5 (Vulnerability Monitoring and Scanning).
Deeper analysis
CVE-2026-6754 is a use-after-free vulnerability (CWE-416) in the JavaScript Engine component of Mozilla Firefox and Thunderbird. It affects versions of Firefox prior to 150, Firefox ESR prior to 115.35 and 140.10, Thunderbird prior to 150 and 140.10. The issue carries a CVSS v3.1 base score of 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H), indicating high severity primarily due to its potential for remote denial-of-service.
Remote attackers can exploit this vulnerability over the network with low complexity, requiring no privileges or user interaction. Successful exploitation leads to a denial of service, such as application crashes or instability, without impacts to confidentiality or integrity.
Mozilla's security advisories (MFSA 2026-30 through 2026-33) and the associated Bugzilla entry (bug 2027541) detail the patch releases that resolve the issue, recommending immediate upgrades to Firefox 150, Firefox ESR 115.35 or 140.10, Thunderbird 150, or Thunderbird 140.10 for mitigation.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-24095
Vulnerability details
Use-after-free in the JavaScript Engine component. This vulnerability was fixed in Firefox 150, Firefox ESR 115.35, Firefox ESR 140.10, Thunderbird 150, and Thunderbird 140.10.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Use-after-free in JS engine directly causes application crashes/instability for remote DoS with no C/I impact, matching Endpoint Denial of Service via Application or System Exploitation.
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Mandates timely installation of software updates to remediate the use-after-free flaw in the JavaScript engine as fixed in Firefox 150 and Thunderbird 150.
Requires receiving and implementing security advisories such as Mozilla's MFSA 2026-30 through 2026-33 to address this vulnerability.
Enables scanning for vulnerable Firefox and Thunderbird versions affected by this use-after-free issue to prioritize 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