Raw vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:NCVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.
Summary
CVE-2026-2783 is a high-severity Type Confusion (CWE-843) vulnerability in Mozilla Firefox. Its CVSS base score is 7.5 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Junk Data (T1001.001); ranked at the 35th 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-3 (Access Enforcement) and AC-4 (Information Flow Enforcement) — 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-2026-2783 is an information disclosure vulnerability stemming from JIT miscompilation in the JavaScript Engine's JIT component. It affects Mozilla Firefox versions prior to 148, Firefox ESR prior to 140.8, Thunderbird prior to 148, and Thunderbird prior to 140.8. The issue is classified under CWE-843 (Access of Resource Using Incompatible Type) and CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor), with a CVSS v3.1 base score of 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N), indicating high severity due to its potential for confidential data exposure.
Remote attackers require no privileges or user interaction to exploit this vulnerability over the network with low complexity. Successful exploitation enables high-impact confidentiality violations, such as leaking sensitive memory contents from the JavaScript engine, potentially exposing user data, tokens, or other process information without affecting integrity or availability.
Mozilla's security advisories (MFSA 2026-13, 2026-15, 2026-16, and 2026-17) and Bugzilla entry 2010943 detail the fix applied 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 risk.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-8503
Vulnerability Data
Information disclosure due to JIT miscompilation in the JavaScript Engine: JIT 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 Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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V1.5.2V15.3.5
Mitigating Controls (NIST 800-53 r5) AI
Access enforcement directly stops unauthorized actors from obtaining sensitive information.
Information flow enforcement structurally prevents sensitive data from reaching unauthorized recipients.
Protection of information at rest prevents unauthorized exposure of stored sensitive data.
Transmission confidentiality mechanisms stop exposure of sensitive data on the wire.
Least privilege reduces the set of actors who can reach sensitive information.
Developer testing and evaluation (including fuzzing and type-aware analysis) directly finds type-confusion flaws before deployment.
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.
A.5.10 only requires awareness, a topic-specific acceptable-use policy stating expected behaviours/monitoring, and procedures referencing classification and other controls; per the owner's explicit rule on labelling and similar dependency-style clauses, this does not itself prevent exposure (CWE-200) unless access/DLP/etc. act on it.
Requiring the return of all physical and electronic assets plus secure deletion of organizational data from personal devices reduces the chance that sensitive information remains accessible to departing personnel.
A.5.12 only defines and communicates a classification scheme so that protection needs can be understood; per the owner's explicit rule, labeling/classification does not itself prevent exposure and requires other controls (e.g. access enforcement) to act on it.
By requiring classification labels and metadata on all information assets, the control makes it harder for sensitive data to be inadvertently exposed because downstream systems and users can recognize and enforce handling rules based on those labels.
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.