CVE-2026-16375
Mozilla Firefox ≤ 140.13.0
Raw vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:HSummary
CVE-2026-16375 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 Browser Session Hijacking (T1185); ranked at the 11th 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 SC-39 (Process Isolation) — see the control section below for these in your framework.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-46211
Vulnerability Data
Site isolation issue in the Networking: HTTP component. This vulnerability was fixed in Firefox 153, Firefox ESR 140.13, Thunderbird 153, and Thunderbird 140.13.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Site isolation bypass (CWE-346) in browser HTTP component directly enables cross-origin session/data access (T1185) and can be triggered via malicious web content in drive-by attacks (T1189).
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
Mitigating Controls (NIST 800-53 r5) AI
Enforces information flow policies between distinct security domains (origins), directly blocking the cross-site data access that results from the site-isolation flaw.
Requires process isolation so that code and data from different sites cannot interfere with each other, mitigating the root cause of the Networking:HTTP isolation bypass.
Implements boundary protection mechanisms that can be configured to enforce origin-based separation at the network and application layers, limiting exploitation of the origin-validation error.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Authentication directly verifies the source of users/services/hardware, mitigating origin validation failures.
Verifying identity assertions enforces origin validation for conveyed claims.
Documenting authorized flows supports origin validation by defining expected sources.
Protecting networks from unauthorized access requires origin checks on communication sources.
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.
Network segregation reduces exposure but does not directly validate origins.
Application security requirements explicitly call for origin validation of inputs and communications.
Secure architecture principles encourage origin checks but do not mandate them.
Secure coding practices include implementing proper origin validation to prevent spoofing.