CVE-2026-4700
Published: 24 March 2026
Summary
CVE-2026-4700 is a critical-severity Authentication Bypass Using an Alternate Path or Channel (CWE-288) vulnerability in Mozilla Firefox. Its CVSS base score is 9.8 (Critical).
Operationally, exploitation aligns with the MITRE ATT&CK technique Drive-by Compromise (T1189); ranked at the 6.8th 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-2 (Flaw Remediation) and RA-5 (Vulnerability Monitoring and Scanning).
Threat & Defense at a Glance
Threat & Defense Details
Mitigating Controls (NIST 800-53 r5)AI
Directly requires timely flaw remediation by patching Firefox and Thunderbird to fixed versions (149 or ESR 140.9) to eliminate the HTTP networking mitigation bypass in CVE-2026-4700.
Addresses vulnerability by scanning systems to identify instances running vulnerable versions of Firefox or Thunderbird affected by CVE-2026-4700.
Ensures awareness of security advisories like Mozilla MFSA 2026-20, 22, 23, 24 detailing CVE-2026-4700 to initiate patching.
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
CVE enables remote client-side exploitation via malicious HTTP responses (no auth/interaction), directly mapping to drive-by compromise and client execution techniques in browser/email clients.
NVD Description
Mitigation bypass in the Networking: HTTP component. This vulnerability was fixed in Firefox 149, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.
Deeper analysisAI
CVE-2026-4700 is a mitigation bypass vulnerability in the Networking: HTTP component of Mozilla Firefox and Thunderbird. It affects versions of Firefox prior to 149, Firefox ESR prior to 140.9, Thunderbird prior to 149, and Thunderbird prior to 140.9. The issue is classified under CWE-288 (Authentication Bypass Using an Alternate Path or Channel) with a CVSS v3.1 base score of 9.8, indicating critical severity due to its network accessibility, low complexity, lack of required privileges or user interaction, and high impacts on confidentiality, integrity, and availability.
Any unauthenticated remote attacker can exploit this vulnerability over the network with low complexity and no user interaction. Successful exploitation allows the attacker to bypass security mitigations in the HTTP networking stack, potentially leading to arbitrary code execution, data theft, or system compromise on affected browsers or email clients.
Mozilla security advisories (MFSA 2026-20, 22, 23, 24) and the associated Bugzilla entry (2003766) confirm the vulnerability was addressed in the specified fixed releases. Mitigation requires updating to Firefox 149, Firefox ESR 140.9, Thunderbird 149, or Thunderbird 140.9, with no additional workarounds mentioned.
Details
- CWE(s)