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.

CVSS v3 4.6 MEDIUM

4.6^/10

CVSS v3 : MEDIUM

Vector :

Exploitability : 0.9 / Impact : 3.6

Attack Vector PHYSICAL

Attack Complexity LOW

Privileges Required NONE

User Interaction NONE

Confidentiality Impact HIGH

Integrity Impact NONE

Availability Impact NONE

Scope UNCHANGED

References

Link	Resource
https://elm-chan.org/fsw/ff/	Product
https://github.com/runZeroInc/vulns-2026-fatfs-chance	Third Party Advisory Exploit
https://www.runzero.com/advisories/fatfs-uninit-cluster-exposure-cve-2026-6686/	Third Party Advisory
https://www.runzero.com/blog/fatfs-bugs/	Third Party Advisory Exploit
https://github.com/runZeroInc/vulns-2026-fatfs-chance	Third Party Advisory Exploit

Configurations

Configuration 1 (hide)

cpe:2.3:a:elm-chan:fatfs:*:*:*:*:*:*:*:*

History

25 Oct 2026, 17:10

Type	Values Removed	Values Added
Summary		(es) FatFs R0.16 y anteriores contiene una exposición de clúster no inicializado cuando f_lseek() extiende archivos más allá del EOF sin rellenar con ceros los clústeres recién asignados. Esto se mapea a CWE-908 (Uso de Recurso No Inicializado). Vector CVSS v3.1 estimado: CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N (4.6, Medio). Los vectores SSVC de CISA estimados son Explotación: PoC, Impacto Técnico: Parcial.

Information

Published : 2026-07-01 15:17

Updated : 2026-10-25 17:10

NVD link : CVE-2026-6686

Mitre link : CVE-2026-6686

CVE.ORG link : CVE-2026-6686

JSON object : View

Products Affected

elm-chan

fatfs

CWE

CWE-908

Use of Uninitialized Resource

{"id": "CVE-2026-6686", "cveTags": [], "metrics": {"ssvcV203": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "ssvcData": {"id": "CVE-2026-6686", "role": "CISA Coordinator", "options": [{"exploitation": "poc"}, {"automatable": "no"}, {"technicalImpact": "partial"}], "version": "2.0.3", "timestamp": "2026-07-01T15:05:23.138301Z"}}], "cvssMetricV31": [{"type": "Secondary", "source": "44488dab-36db-4358-99f9-bc116477f914", "cvssData": {"scope": "UNCHANGED", "version": "3.1", "baseScore": 4.6, "attackVector": "PHYSICAL", "baseSeverity": "MEDIUM", "vectorString": "CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N", "integrityImpact": "NONE", "userInteraction": "NONE", "attackComplexity": "LOW", "availabilityImpact": "NONE", "privilegesRequired": "NONE", "confidentialityImpact": "HIGH"}, "impactScore": 3.6, "exploitabilityScore": 0.9}]}, "affected": [{"source": "44488dab-36db-4358-99f9-bc116477f914", "affectedData": [{"vendor": "ChaN", "product": "FatFs", "versions": [{"status": "affected", "version": "0", "versionType": "custom", "lessThanOrEqual": "R0.16"}], "defaultStatus": "unaffected"}]}], "published": "2026-07-01T15:17:12.763", "references": [{"url": "https://elm-chan.org/fsw/ff/", "tags": ["Product"], "source": "44488dab-36db-4358-99f9-bc116477f914"}, {"url": "https://github.com/runZeroInc/vulns-2026-fatfs-chance", "tags": ["Third Party Advisory", "Exploit"], "source": "44488dab-36db-4358-99f9-bc116477f914"}, {"url": "https://www.runzero.com/advisories/fatfs-uninit-cluster-exposure-cve-2026-6686/", "tags": ["Third Party Advisory"], "source": "44488dab-36db-4358-99f9-bc116477f914"}, {"url": "https://www.runzero.com/blog/fatfs-bugs/", "tags": ["Third Party Advisory", "Exploit"], "source": "44488dab-36db-4358-99f9-bc116477f914"}, {"url": "https://github.com/runZeroInc/vulns-2026-fatfs-chance", "tags": ["Third Party Advisory", "Exploit"], "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0"}], "vulnStatus": "Analyzed", "weaknesses": [{"type": "Secondary", "source": "44488dab-36db-4358-99f9-bc116477f914", "description": [{"lang": "en", "value": "CWE-908"}]}], "descriptions": [{"lang": "en", "value": "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."}, {"lang": "es", "value": "FatFs R0.16 y anteriores contiene una exposici\u00f3n de cl\u00faster no inicializado cuando f_lseek() extiende archivos m\u00e1s all\u00e1 del EOF sin rellenar con ceros los cl\u00fasteres reci\u00e9n asignados. Esto se mapea a CWE-908 (Uso de Recurso No Inicializado). Vector CVSS v3.1 estimado: CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N (4.6, Medio). Los vectores SSVC de CISA estimados son Explotaci\u00f3n: PoC, Impacto T\u00e9cnico: Parcial."}], "lastModified": "2026-10-25T17:10:00.197", "configurations": [{"nodes": [{"negate": false, "cpeMatch": [{"criteria": "cpe:2.3:a:elm-chan:fatfs:*:*:*:*:*:*:*:*", "vulnerable": true, "matchCriteriaId": "B99160BB-C4F5-4DA0-9FC9-0723E0633E00", "versionEndIncluding": "r0.16"}], "operator": "OR"}]}], "sourceIdentifier": "44488dab-36db-4358-99f9-bc116477f914"}