CVE-2026-7321
Published: 28 April 2026
Summary
CVE-2026-7321 is a critical-severity Classic Buffer Overflow (CWE-120) vulnerability in Mozilla Firefox. Its CVSS base score is 9.6 (Critical).
Operationally, exploitation aligns with the MITRE ATT&CK technique Drive-by Compromise (T1189); ranked at the 17.1th 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 CM-7 (Least Functionality) and SI-2 (Flaw Remediation).
Deeper analysis
CVE-2026-7321 is a sandbox escape vulnerability stemming from incorrect boundary conditions, classified under CWE-120 (Buffer Copy without Bounds Check), in the WebRTC Networking component. It affects Mozilla Firefox, Thunderbird, Firefox ESR, and Thunderbird ESR prior to their respective fixed versions: Firefox 150, Thunderbird 150, Firefox ESR 140.10.1, and Thunderbird ESR 140.10.1. The vulnerability carries a CVSS v3.1 base score of 9.6, reflecting its critical severity due to network accessibility, low attack complexity, and high potential impact.
An attacker can exploit this vulnerability remotely over the network without privileges by tricking a user into interacting with malicious content, such as visiting a specially crafted webpage that triggers the WebRTC Networking flaw. Successful exploitation changes the scope from the sandboxed context to the broader system, granting high confidentiality, integrity, and availability impacts, potentially allowing arbitrary code execution, data theft, or full system compromise on the targeted machine.
Mozilla's security advisories (MFSA 2026-30, 2026-33, 2026-36, and 2026-39) and the associated Bugzilla entry (bug 2029461) confirm the issue was addressed in the specified versions. Security practitioners should prioritize updating affected browsers and email clients to the patched releases, disable WebRTC if not required, and educate users on avoiding suspicious links or media streams.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-26058
Vulnerability details
Sandbox escape due to incorrect boundary conditions in the WebRTC: Networking component. This vulnerability was fixed in Firefox 150, Thunderbird 150, Firefox ESR 140.10.1, and Thunderbird 140.10.1.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
The CVE describes a browser sandbox escape via buffer overflow in WebRTC, triggered by visiting a malicious webpage, directly enabling Drive-by Compromise (T1189) for initial access and Exploitation for Client Execution (T1203) to achieve arbitrary code execution outside the sandbox.
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Directly requires identification, reporting, and correction of flaws like the buffer copy without bounds check in the WebRTC networking component via timely patching.
Prohibits or restricts unnecessary functions such as WebRTC to eliminate exposure to the vulnerable networking component.
Implements memory safeguards that protect against unauthorized code execution stemming from the boundary condition error in WebRTC.