CVE-2026-6686
Elm-Chan Fatfs ≤ r0.16
Raw vector
CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:NSummary
CVE-2026-6686 is a medium-severity Use of Uninitialized Resource (CWE-908) vulnerability in Elm-Chan Fatfs. Its CVSS base score is 4.6 (Medium).
Operationally, ranked at the 30th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.
The strongest mitigations our analysis identified map to SC-4 (Information in Shared System Resources) and SI-2 (Flaw Remediation) — see the control section below for these in your framework.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-40998
Vulnerability Data
FatFs R0.16 and earlier contains an uninitialized cluster exposure when f_lseek() extends files beyond EOF without zero-filling newly allocated clusters. This maps to CWE-908 (Use of Uninitialized Resource). Estimated CVSS v3.1 vector: CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N (4.6, Medium). The estimated CISA SSVC vectors…
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are Exploitation: PoC, Technical Impact: Partial.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Insufficient information to map techniques.Likely ATT&CK TechniquesAI
Techniques this vulnerability likely enables, inferred from its description, weakness type, and attributed-actor tradecraft. Confidence is per-technique.
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
Mitigating Controls (NIST 800-53 r5) AI
Directly prevents residual data exposure by ensuring shared storage clusters (system resources) are cleared before reuse when files are extended.
Requires timely patching or replacement of the vulnerable FatFs implementation to eliminate the missing zero-fill on cluster allocation.
Limits blast radius of the disclosure by isolating processes so one process cannot read uninitialized clusters belonging to another via the file system.
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 activities such as static analysis and code review directly prevent use of uninitialized resources while also addressing many other 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 and acceptance can detect uninitialized resource usage through dynamic analysis and fuzzing.
Secure development life cycle mandates initialization checks and static analysis that can catch uninitialized resource use.
Application security requirements can specify mandatory initialization of variables and resources before use.
Secure system architecture and engineering principles include defensive coding practices that prevent use of uninitialized memory or objects.
Secure coding standards directly require explicit initialization of all variables and resources, substantially mitigating CWE-908.