CVE-2026-2790
Published: 24 February 2026
Summary
CVE-2026-2790 is a critical-severity Origin Validation Error (CWE-346) 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 7.3th 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 RA-5 (Vulnerability Monitoring and Scanning) and SI-2 (Flaw Remediation).
Threat & Defense at a Glance
Threat & Defense Details
Mitigating Controls (NIST 800-53 r5)AI
Directly mandates timely patching of the same-origin policy bypass flaw in the Firefox and Thunderbird Networking: JAR component to prevent exploitation.
Requires vulnerability scanning to identify systems with vulnerable browser versions and prioritized remediation via patching.
Ensures receipt and dissemination of Mozilla security advisories like MFSA 2026-13 for the CVE, enabling prompt flaw remediation.
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
CVE describes a remotely exploitable client-side SOP bypass in Firefox/Thunderbird (CWE-346) with no auth/UI required and full CIA impact; directly enables T1203 (Exploitation for Client Execution) and T1189 (Drive-by Compromise) as the primary attack techniques.
NVD Description
Same-origin policy bypass in the Networking: JAR component. This vulnerability was fixed in Firefox 148, Firefox ESR 140.8, Thunderbird 148, and Thunderbird 140.8.
Deeper analysisAI
CVE-2026-2790 is a same-origin policy bypass vulnerability in the Networking: JAR component of Mozilla Firefox and Thunderbird. It affects versions of Firefox prior to 148, Firefox ESR prior to 140.8, Thunderbird prior to 148, and Thunderbird prior to 140.8. 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) and is associated with CWE-346 (Origin Validation Error), with additional NVD-CWE-noinfo mapping.
The vulnerability enables exploitation over the network by unauthenticated attackers with low complexity and no user interaction required. Successful exploitation allows attackers to bypass the same-origin policy, potentially leading to high impacts on confidentiality, integrity, and availability, such as unauthorized access to sensitive data, modification of web content, or disruption of browser functionality.
Mozilla security advisories (MFSA 2026-13, 15, 16, and 17) and the associated Bugzilla entry detail the patch, which resolves the issue in Firefox 148, Firefox ESR 140.8, Thunderbird 148, and Thunderbird 140.8. Security practitioners should prioritize updating affected products to these versions or later to mitigate the vulnerability.
Details
- CWE(s)