CVE-2026-6747
Published: 21 April 2026
Summary
CVE-2026-6747 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 32.0th 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 SI-16 (Memory Protection).
Deeper analysis
CVE-2026-6747 is a use-after-free vulnerability (CWE-416) in the WebRTC 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. 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 denial-of-service impacts.
Remote attackers can exploit this vulnerability over the network with low complexity, requiring no privileges, authentication, or user interaction. Successful exploitation leads to a high-impact denial of service, such as application crashes, without affecting confidentiality or integrity.
Mozilla's security advisories (MFSA 2026-30, 32, 33, and 34) and the associated Bugzilla entry detail the fix applied in the specified versions. Mitigation involves updating to Firefox 150, Firefox ESR 140.10, Thunderbird 150, or Thunderbird 140.10 as applicable.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-24088
Vulnerability details
Use-after-free in the WebRTC 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?
Use-after-free in WebRTC enables remote exploitation causing browser crashes and denial of service with no user interaction, directly matching T1499.004 Application or System Exploitation.
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Directly mitigates the use-after-free vulnerability by requiring timely patching to the fixed versions of Firefox and Thunderbird as specified in Mozilla advisories.
Implements memory protection mechanisms such as ASLR and DEP that hinder exploitation of the WebRTC use-after-free leading to denial-of-service crashes.
Ensures monitoring of security advisories like MFSA 2026-30 to identify and remediate the vulnerable WebRTC component in affected browser versions.
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