Raw vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:HSummary
CVE-2026-16355 is a critical-severity Type Confusion (CWE-843) vulnerability in Mozilla Firefox. Its CVSS base score is 9.8 (Critical).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Client Execution (T1203); ranked at the 33th 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 RA-5 (Vulnerability Monitoring and Scanning) and SI-2 (Flaw Remediation) — see the control section below for these in your framework.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-46203
Vulnerability Data
JIT miscompilation in the JavaScript Engine: JIT component. This vulnerability was fixed in Firefox 153, Firefox ESR 115.38, Firefox ESR 140.13, Thunderbird 153, and Thunderbird 140.13.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Type confusion in JS JIT enables client-side RCE via malicious JavaScript (T1203, T1059.007).
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
Mitigating Controls (NIST 800-53 r5) AI
Directly requires timely application of the vendor-supplied patches that remediate the JIT type-confusion flaw in CVE-2026-16355.
Mandates continuous vulnerability scanning to identify unpatched Firefox/Thunderbird instances still containing the CWE-843 JIT miscompilation.
Establishes usage restrictions and implementation guidance for mobile code (JavaScript) that can reduce exposure to JIT engine exploitation.
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.
Secure SDLC practices directly prevent type-confusion flaws via safe typing, static analysis, and code review while the control itself addresses many additional weaknesses.
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.
Security testing in development can detect type-confusion vulnerabilities through fuzzing and static analysis.
Secure SDLC mandates type-safe design and review that can catch type-confusion flaws.
Application security requirements can specify strong typing and interface contracts that reduce type confusion.
Secure architecture principles promote type-safe languages and memory-safety mechanisms that mitigate type confusion.
Secure coding standards directly forbid unsafe type casts and require static-analysis checks for type confusion.