CVE-2026-6748
Published: 21 April 2026
Summary
CVE-2026-6748 is a critical-severity Use of Uninitialized Variable (CWE-457) vulnerability in Mozilla Firefox. Its CVSS base score is 9.8 (Critical).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Client Execution (T1203); ranked at the 19.8th 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).
Threat & Defense at a Glance
Threat & Defense Details
Mitigating Controls (NIST 800-53 r5)AI
Directly mitigates CVE-2026-6748 by requiring timely installation of vendor patches to fix the uninitialized memory vulnerability in Firefox and Thunderbird Web Codecs.
Implements memory protection mechanisms like ASLR and DEP that reduce the exploitability of uninitialized memory disclosures and corruption in the Web Codecs component.
Enables scanning to identify systems running vulnerable versions of Firefox or Thunderbird affected by this uninitialized memory issue, facilitating remediation.
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Uninitialized memory vulnerability (CWE-457) in Firefox/Thunderbird web codecs component enables remote code execution in a client application with no privileges or user interaction required, directly mapping to Exploitation for Client Execution (T1203).
NVD Description
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.
Deeper analysisAI
CVE-2026-6748 is an uninitialized memory vulnerability, classified under CWE-457, in the Audio/Video: Web Codecs component of Mozilla Firefox and Thunderbird. It affects versions of Firefox prior to 150, Firefox ESR prior to 140.10, Thunderbird prior to 150, and Thunderbird prior to 140.10. Published on 2026-04-21, the issue 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 severity due to its potential for severe impacts.
The vulnerability enables exploitation by a remote attacker over the network with low attack complexity, requiring no privileges, user interaction, or scope changes. Successful exploitation can result in high confidentiality, integrity, and availability impacts on the affected system.
Mozilla advisories MFSA2026-30, MFSA2026-32, MFSA2026-33, and MFSA2026-34 document the patch, confirming fixes in Firefox 150, Firefox ESR 140.10, Thunderbird 150, and Thunderbird 140.10. Additional technical details are available in Bugzilla entry 2022604. Security practitioners should prioritize updating to these versions to mitigate the risk.
Details
- CWE(s)