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    CVE-2026-6686

    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.

    Published:Jul 1, 2026
    Last Modified:Jul 6, 2026
    EPS:Jul 1, 2026
    EPSS Score:0.00177
    CVSS Score:4.6

    Affected Products

    Vendor
    Chan
    Product
    Fatfs

    Exploits

    https://github.com/runZeroInc/vulns-2026-fatfs-chancehttps://www.runzero.com/blog/fatfs-bugs/https://github.com/runZeroInc/vulns-2026-fatfs-chance

    Common Weakness Enumeration

    CWE-908 Use of Uninitialized Resource

    Common Attack Pattern Enumeration and Classification (CAPEC)

    No CAPEC recorded yet

    Related CVEs

    CVE-2026-6688 (CVSS 7.6) — FatFs R0.16 and earlier contains a downstream-caller vulnerability pattern associated with FatFs long filename…
    CVE-2026-6687 (CVSS 7.6) — FatFs R0.16 and earlier contains a stack overflow bug in f_getlabel() because exFAT label length (XDIR_NumLabe…
    CVE-2026-6685 — This CVE ID has been rejected or withdrawn by its CVE Numbering Authority following a notification that the vu…
    CVE-2026-6684 (CVSS 4.6) — FatFs prior to R0.16 that use GPT scanning with 'FF_LBA64 = 1' contains an issue where an unbounded loop count…
    CVE-2026-6683 (CVSS 4.6) — FatFs R0.16 and earlier contains a divide-by-zero in exFAT sync logic bug when crafted metadata causes n_faten…
    CVE-2026-6682 (CVSS 7.6) — In FatFS R0.16 and earlier contains a FAT32 integer overflow bug in mount_volume() where fasize *= fs->n_fats …

    Common Vulnerability Scoring System

    Attack Vector
    Network
    Adjacent
    Local
    Physical
    Privileges Required
    None
    Low
    High
    User Interaction
    None
    Required
    Scope
    Unchanged
    Changed
    Confidentiality
    None
    Low
    High
    Integrity
    None
    Low
    High
    Availability
    None
    Low
    High