CVE-2026-6751
Published: 21 April 2026
Summary
CVE-2026-6751 is a high-severity Use of Uninitialized Variable (CWE-457) vulnerability in Mozilla Firefox. Its CVSS base score is 7.3 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Drive-by Compromise (T1189); ranked at the 22.4th 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-2026-6751 is an uninitialized memory vulnerability (CWE-457) in the Audio/Video: Web Codecs component of Mozilla Firefox and Thunderbird products. It affects versions prior to Firefox 150, Firefox ESR 140.10, Thunderbird 150, and Thunderbird 140.10. The issue was publicly disclosed on 2026-04-21 and carries a CVSS v3.1 base score of 7.3 (AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L), indicating high severity due to its network accessibility and lack of prerequisites for exploitation.
Remote attackers can exploit this vulnerability without authentication or user interaction by targeting the Web Codecs API, potentially leading to limited disclosure of sensitive information, minor integrity modifications, or partial denial of service through memory corruption. The unchanged scope suggests impacts remain within the affected browser process.
Mozilla's security advisories (MFSA 2026-30 through 2026-34) and the associated Bugzilla entry detail the fix applied in the specified versions, recommending immediate upgrades to patched releases for mitigation. No workarounds are mentioned in the provided references.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-24092
Vulnerability details
Uninitialized memory in the Audio/Video: Web Codecs component. This vulnerability was fixed in Firefox 150, Firefox ESR 140.10, Thunderbird 150, and Thunderbird 140.10.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Client-side memory corruption in browser Web Codecs API enables remote exploitation via web content for drive-by compromise (T1189) and client application execution (T1203).
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Timely identification, reporting, and correction of flaws like the uninitialized memory in Web Codecs directly prevents exploitation of CVE-2026-6751 through patching to fixed versions.
Memory protection mechanisms such as ASLR, DEP, and stack canaries comprehensively mitigate exploitation of uninitialized memory vulnerabilities like CVE-2026-6751 by disrupting reliable memory corruption attacks.
Vulnerability monitoring and scanning detects deployed systems vulnerable to CVE-2026-6751, enabling proactive remediation before exploitation.