CVE-2026-6758
Published: 21 April 2026
Summary
CVE-2026-6758 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 16.3th 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 RA-5 (Vulnerability Monitoring and Scanning) and SI-16 (Memory Protection).
Threat & Defense at a Glance
Threat & Defense Details
Mitigating Controls (NIST 800-53 r5)AI
Directly mandates timely patching and flaw remediation for the specific use-after-free vulnerability fixed in Firefox and Thunderbird version 150.
Provides memory protection mechanisms that prevent unauthorized access to freed memory, comprehensively mitigating use-after-free exploits like CVE-2026-6758.
Requires vulnerability scanning to identify and prioritize remediation of systems with vulnerable Firefox or Thunderbird versions affected by this CVE.
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Use-after-free in browser WebAssembly component directly enables remote exploitation causing application crashes, mapping to Endpoint Denial of Service via Application or System Exploitation.
NVD Description
Use-after-free in the JavaScript: WebAssembly component. This vulnerability was fixed in Firefox 150 and Thunderbird 150.
Deeper analysisAI
CVE-2026-6758 is a use-after-free vulnerability (CWE-416) in the JavaScript WebAssembly component of Mozilla Firefox and Thunderbird. Published on 2026-04-21, it 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 with primary impact on availability. The issue was addressed in Firefox version 150 and Thunderbird version 150.
Remote attackers can exploit this vulnerability over the network with low attack complexity, requiring no privileges, user interaction, or special scope changes. Successful exploitation results in denial of service, such as browser or application crashes, without affecting confidentiality or integrity.
Mozilla's security advisories MFSA2026-30 and MFSA2026-33 document the patch, recommending upgrade to Firefox 150 or Thunderbird 150 for mitigation. Further technical details are available in Bugzilla entry 2013619.
Details
- CWE(s)