CVE-2026-6688

Summary

FatFs R0.16 and earlier contains a downstream-caller vulnerability pattern associated with FatFs long filename handling. With LFN enabled, fno.fname can be up to 255 characters; many callers copy it into short fixed buffers without bounds checks, causing overflow. This maps to CWE-120 (Buffer Copy without Checking Size of Input). 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 vectors are Exploitation: PoC, Technical Impact: Total.

Affected Software

Weaknesses

• CWE-120: CWE-120 Buffer Copy without Checking Size of Input

ADP Enrichment

CISA ADP Vulnrichment

• SSVC:
• Exploitation: poc
  • Automatable: no
  • Technical Impact: total

Additional References

• https://github.com/runZeroInc/vulns-2026-fatfs-chance

References

• https://www.runzero.com/blog/fatfs-bugs/
• https://github.com/runZeroInc/vulns-2026-fatfs-chance
• https://elm-chan.org/fsw/ff/
• https://www.runzero.com/advisories/fatfs-long-fn-of-downstream-cve-2026-6688/

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