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 13.6th 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).
Deeper analysis
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.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-8443
Vulnerability details
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.
- CWE(s)
Related Threats
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.
CVEs Like This One
Affected Assets
Mitigating Controls
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.
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 (3 rules)
- V-248574 YUM must be configured to prevent the installation of patches, service packs, device drivers, or OL 8 system components that have not been digitally signed using a certificate that is recognized and approved by the organization. via CWE-346
- V-248575 OL 8 must prevent the installation of software, patches, service packs, device drivers, or operating system components of local packages without verification they have been digitally signed using a certificate that is issued by a Certificate Authority (CA) that is recognized and approved by the organization. via CWE-346
- V-248827 OL 8 must not have the rsh-server package installed. via CWE-346