CVE-2026-2790
Mozilla Firefox ≤ 140.8.0
Raw vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:HCVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.
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, ranked at the 13th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified map to AC-4 (Information Flow Enforcement) and IA-3 (Device Identification and Authentication) — see the control section below for these in your framework.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
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 Data
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
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Information flow enforcement directly requires validating the source of data before allowing transmission or receipt.
Device identification and authentication mandates verifying the source before establishing connections.
Session authenticity mechanisms require validation that communications originate from the expected party.
Boundary protection at interfaces enforces checks on the origin of incoming communications.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Network security controls enforce origin validation at network boundaries.
Security of network services includes validating the authenticity of service endpoints.
A.8.26 requires identifying and specifying requirements for resilience against malicious attacks including SQL injections and input validation (items d, j), plus related protections (authentication, segregation, cryptography per 8.24), which can address some but not most origin validation scenarios such as those involving untrusted cross-origin requests or implicit trust in sources.
A.8.27 mandates security-by-design principles (defense-in-depth, least privilege, assume-breach, distrust-external-input, zero-trust verification) plus design reviews that can catch and block origin-validation gaps in many common cases, but leaves a bounded remainder (e.g. protocol-level or third-party component origin errors not surfaced by the organization's review process).
Secure coding practices include implementing proper origin validation to prevent spoofing.
Secure authentication verifies identity but does not address origin validation of arbitrary data flows.
Hardening callouts derived
DISA STIG baselines are authored against specific weaknesses. Where this CVE cites a broad weakness class, the mapping is not asserted at that abstraction (owner ruling, 2026-09-25: grade only at Base and below), so no rule is shown here rather than a rule shown against the wrong grain.
- No fine-grained STIG row for CWE-346, a class-level weakness, and none of its children carries one either.