CVE-2026-6686: medium-severity vulnerability in ChaN FatFs
FatFs Use of Uninitialized Clusters After Seek Past EOF
Published
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13Vexday Risk Score
No sign of exploitation. No public exploitation artifact known so far.
ssvc Trackcvss 4.6epss 0.3%
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 are Exploitation: PoC, Technical Impact: Partial.
CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Affected products
ChaN · FatFsRelated CVEs — ChaN FatFs
In the same product, most dangerous first.
CVE-2026-6687HIGHFatFs Stack Buffer Overflow via Uncapped exFAT Label LengthEPSS 0.3%CVE-2026-6688HIGHFatFs Buffer Overflow via Unbounded LFN Filename CopyEPSS 0.3%CVE-2026-6682HIGHFatFs Integer Overflow in FAT32 Volume MountEPSS 0.3%CVE-2026-6684MEDIUMFatFs Infinite Loop in GPT Partition ScanEPSS 0.3%CVE-2026-6683MEDIUMFatFs Divide-by-Zero in exFAT SyncEPSS 0.3%