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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.
Lifecycle PUBLISHED1 preserved revisionFact urn:baitaphish:canonical-cve-fact-revision:v2:fe5fff48ef125dadef6e5a06324eeb3b3713b38d76b36c0bd5e1e5e004e3424b
Known exploited
Not asserted
Disputed
No
Stale source
No
Conflicts
0

Affected products and versions

1 source assertion
{"defaultStatus":"unaffected","product":"FatFs","vendor":"ChaN","versions":[{"lessThanOrEqual":"R0.16","status":"affected","version":"0","versionType":"custom"}]}
  • cve_program_cvelist_v5affected
    urn:baitaphish:normalized-source-record:v2:fc76b7958f1b666c5acceb9d81598ac2e6470c226cc0eddc48569cf97b1a10e4 · sha256:d640546635ed3006… · /containers/cna/affected/0

Provider-owned CVSS observations

1 source assertion
{"metric":{"attackComplexity":"LOW","attackVector":"PHYSICAL","availabilityImpact":"NONE","baseScore":4.6,"baseSeverity":"MEDIUM","confidentialityImpact":"HIGH","integrityImpact":"NONE","privilegesRequired":"NONE","scope":"UNCHANGED","userInteraction":"NONE","vectorString":"CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N","version":"3.1"},"metric_type":"cvssV3_1"}
  • cve_program_cvelist_v5cvss
    urn:baitaphish:normalized-source-record:v2:fc76b7958f1b666c5acceb9d81598ac2e6470c226cc0eddc48569cf97b1a10e4 · sha256:d640546635ed3006… · /containers/cna/metrics/0/cvssV3_1

CWE assertions

1 source assertion
{"cweId":"CWE-908","description":"CWE-908 Use of uninitialized resource","lang":"en","type":"CWE"}
  • cve_program_cvelist_v5cwe
    urn:baitaphish:normalized-source-record:v2:fc76b7958f1b666c5acceb9d81598ac2e6470c226cc0eddc48569cf97b1a10e4 · sha256:d640546635ed3006… · /containers/cna/problemTypes/0/descriptions/0

Source references

5 source assertions
{"tags":["product"],"url":"https://elm-chan.org/fsw/ff/"}
  • cve_program_cvelist_v5reference
    urn:baitaphish:normalized-source-record:v2:fc76b7958f1b666c5acceb9d81598ac2e6470c226cc0eddc48569cf97b1a10e4 · sha256:d640546635ed3006… · /containers/cna/references/2
{"tags":["exploit"],"url":"https://github.com/runZeroInc/vulns-2026-fatfs-chance"}
  • cve_program_cvelist_v5reference
    urn:baitaphish:normalized-source-record:v2:fc76b7958f1b666c5acceb9d81598ac2e6470c226cc0eddc48569cf97b1a10e4 · sha256:d640546635ed3006… · /containers/adp/0/references/0
{"tags":["technical-description"],"url":"https://github.com/runZeroInc/vulns-2026-fatfs-chance"}
  • cve_program_cvelist_v5reference
    urn:baitaphish:normalized-source-record:v2:fc76b7958f1b666c5acceb9d81598ac2e6470c226cc0eddc48569cf97b1a10e4 · sha256:d640546635ed3006… · /containers/cna/references/1
{"tags":["third-party-advisory"],"url":"https://www.runzero.com/advisories/fatfs-uninit-cluster-exposure-cve-2026-6686/"}
  • cve_program_cvelist_v5reference
    urn:baitaphish:normalized-source-record:v2:fc76b7958f1b666c5acceb9d81598ac2e6470c226cc0eddc48569cf97b1a10e4 · sha256:d640546635ed3006… · /containers/cna/references/3
{"tags":["third-party-advisory"],"url":"https://www.runzero.com/blog/fatfs-bugs/"}
  • cve_program_cvelist_v5reference
    urn:baitaphish:normalized-source-record:v2:fc76b7958f1b666c5acceb9d81598ac2e6470c226cc0eddc48569cf97b1a10e4 · sha256:d640546635ed3006… · /containers/cna/references/0

Attribution and limitations

  • CVE Program CVEList V5: Reproduce the MITRE copyright designation and CVE license in copies. Source →

Provider severity values are preserved separately. Baitaphish does not convert them into a risk rating, infer affected products, or treat EPSS as observed exploitation.

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