Cyber Resilience

CVE-2026-6687

Memory Safety in Elm-Chan Fatfs ≤ r0.16

Public PoCMemory Safety
Published
01 July 2026
Modified
02 July 2026
Patch / advisory
View advisory
CVSS Score v3.1 7.6
Click a component to see what it means
Raw vectorCVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
EPSS Score 0.0046 37th percentile
Risk Priority 55 floored blend · peak EPSS

Summary

CVE-2026-6687 is a high-severity Stack-based Buffer Overflow (CWE-121) vulnerability in Elm-Chan Fatfs. Its CVSS base score is 7.6 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Privilege Escalation (T1068); ranked at the 37th 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 SI-10 (Information Input Validation) and SI-16 (Memory Protection) — see the control section below for these in your framework.

EU & UK References

Vulnerability Data

FatFs R0.16 and earlier contains a stack overflow bug in f_getlabel() because exFAT label length (XDIR_NumLabel) is trusted without enforcing spec maximums. This maps to CWE-121 (Stack-based Buffer Overflow). Estimated CVSS v3.1 vector: CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H (7.6, High). The estimated CISA SSVC…

more

vectors are Exploitation: PoC, Technical Impact: Total.

CWE(s)
CWE-121

Related Threats

MITRE ATT&CK Enterprise TechniquesAI

T1068 Exploitation for Privilege Escalation Privilege Escalation
Adversaries may exploit software vulnerabilities in an attempt to elevate privileges.
attack.mitre.org →
Why these techniques?

Stack buffer overflow in filesystem label parsing enables local code execution/privilege escalation when a malicious exFAT image is processed (physical access vector).

Confidence: MEDIUM · MITRE ATT&CK Enterprise v19.0

Likely ATT&CK TechniquesAI

Techniques this vulnerability likely enables, inferred from its description, weakness type, and attributed-actor tradecraft. Confidence is per-technique.

T1200 Hardware Additions Initial Accessconfidence: HIGH
Stack overflow in exFAT label parsing is triggered by inserting crafted removable media (AV:P).
attack.mitre.org →
T1091 Replication Through Removable Media Lateral Movementconfidence: HIGH
Vulnerability in FatFs f_getlabel() enables code execution or impact when malicious exFAT volume label is processed on media insertion.
attack.mitre.org →
inferred from description + CWE · MITRE ATT&CK Enterprise v19.0

CVEs Like This One

CVE-2026-6688Same product: Elm-Chan Fatfs
CVE-2026-6682Same product: Elm-Chan Fatfs
CVE-2026-6684Same product: Elm-Chan Fatfs
CVE-2026-6686Same product: Elm-Chan Fatfs
CVE-2026-6683Same product: Elm-Chan Fatfs
CVE-2026-0413Shared CWE-121
CVE-2025-70616Shared CWE-121
CVE-2026-23995Shared CWE-121
CVE-2026-32708Shared CWE-121
CVE-2026-24085Shared CWE-121

Affected Assets

elm-chan
fatfs
≤ r0.16

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)
  • SI-10 Information Input Validation
  • SI-16 Memory Protection
  • SC-39 Process Isolation
Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)
  • 2 hardening rules · 2 OS baselines
Validate
Prove the fix (OWASP ASVS)

—

Mitigating Controls (NIST 800-53 r5) AI

SI-10 Information Input Validation good match
prevent

Directly requires validation of all input fields (including XDIR_NumLabel length) against defined limits before any copy into stack buffers occurs.

SI-16 Memory Protection good match
prevent

Enforces memory-protection mechanisms (e.g., stack canaries, NX, ASLR) that block exploitation of the stack overflow in f_getlabel().

SC-39 Process Isolation partial match
prevent

Process isolation confines the effects of a successful overflow in the FatFs library to the calling process, limiting system-wide impact.

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.

PR.PS-06 mostly match
prevents

Secure-development practices directly prevent introduction of stack buffer overflows.

ID.RA-01 partial match
prevents

Vulnerability scanning can discover stack buffer overflows but does not prevent their introduction.

PR.PS-02 partial match
prevents

Patching eliminates known instances of the weakness after discovery.

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.8.29 Security testing in development and acceptance mostly match
detects

Security testing (fuzzing, static analysis) detects stack overflows before release.

A.8.25 Secure development life cycle partial match
prevents

Secure SDLC mandates buffer-safety practices that directly prevent stack overflows.

A.8.26 Application security requirements partial match
prevents

Application security requirements can specify buffer-size and input-validation rules.

A.8.27 Secure system architecture and engineering principles partial match
prevents

Secure architecture principles include memory-safety and least-privilege stack usage.

A.8.28 Secure coding partial match
prevents

Secure coding standards explicitly forbid unsafe buffer handling that causes CWE-121.

A.8.32 Change management none match
none

Change-management gates can enforce security reviews that catch buffer issues.

References