{"id":"CVE-2026-6686","aliases":["EUVD-2026-40998","GHSA-h94p-vjqx-v7rr"],"status":"published","title":"FatFs Use of Uninitialized Clusters After Seek Past EOF","description":"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.","severity":{"version":"3.1","score":4.6,"vector":"CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N","level":"medium","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-09","score":0.00255,"percentile":0.1719,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":false},"cwes":["CWE-908"],"published":"2026-07-01T13:55:09Z","modified":"2026-10-25T17:10:00Z","products":[{"vendor":"chan","product":"fatfs"},{"vendor":"elm-chan","product":"fatfs"}],"references":[{"url":"https://www.runzero.com/blog/fatfs-bugs/","tags":["third-party-advisory","Third Party Advisory","Exploit"]},{"url":"https://github.com/runZeroInc/vulns-2026-fatfs-chance","tags":["technical-description","exploit","Third Party Advisory","Exploit"]},{"url":"https://elm-chan.org/fsw/ff/","tags":["product","Product"]},{"url":"https://www.runzero.com/advisories/fatfs-uninit-cluster-exposure-cve-2026-6686/","tags":["third-party-advisory","Third Party Advisory"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-6686"},{"url":"https://elm-chan.org/fsw/ff"},{"url":"https://www.runzero.com/advisories/fatfs-uninit-cluster-exposure-cve-2026-6686"},{"url":"https://www.runzero.com/blog/fatfs-bugs"},{"url":"https://github.com/advisories/GHSA-h94p-vjqx-v7rr"}],"sources":{"cve":[{"id":"CVE-2026-6686","title":"FatFs Use of Uninitialized Clusters After Seek Past EOF","description":"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.","status":"published","published":"2026-07-01T13:55:09.072Z","modified":"2026-07-01T15:05:27.926Z","cvss":[{"version":"3.1","score":4.6,"vector":"CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N","level":"medium","assessor":"cna"}],"cwes":["CWE-908"],"updated_at":"2026-11-02T13:50:04.986624Z"}],"euvd":[{"id":"EUVD-2026-40998","description":"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.","status":"published","published":"2026-07-01T13:55:09Z","modified":"2026-07-01T15:05:27Z","cvss":[{"version":"3.1","score":4.6,"vector":"CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N","level":"medium"}],"updated_at":"2026-11-02T18:20:19.829772Z"}],"ghsa":[{"id":"GHSA-h94p-vjqx-v7rr","title":"FatFs R0.16 and earlier contains an uninitialized cluster exposure when f_lseek() extends files...","description":"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.","status":"published","published":"2026-07-01T15:35:20Z","modified":"2026-07-01T15:35:21Z","cvss":[{"version":"3.1","score":4.6,"vector":"CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N","level":"medium"}],"cwes":["CWE-908"],"updated_at":"2026-11-02T15:09:08.409779Z"}],"nvd":[{"id":"CVE-2026-6686","description":"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.","status":"published","published":"2026-07-01T15:17:12.763Z","modified":"2026-10-25T17:10:00.197Z","cvss":[{"version":"3.1","score":4.6,"vector":"CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N","level":"medium","assessor":"secondary"}],"cwes":["CWE-908"],"updated_at":"2026-11-02T14:12:27.199837Z"}]}}