Vulnerability-Lookup

FKIE_CVE-2026-6686

Vulnerability from fkie_nvd - Published: 2026-07-01 15:17 - Updated: 2026-07-02 14:38

Severity

4.6 (Medium) - CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Summary

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.

References

URL	Tags
44488dab-36db-4358-99f9-bc116477f914	https://elm-chan.org/fsw/ff/	Product
44488dab-36db-4358-99f9-bc116477f914	https://github.com/runZeroInc/vulns-2026-fatfs-chance	Third Party Advisory, Exploit
44488dab-36db-4358-99f9-bc116477f914	https://www.runzero.com/advisories/fatfs-uninit-cluster-exposure-cve-2026-6686/	Third Party Advisory
44488dab-36db-4358-99f9-bc116477f914	https://www.runzero.com/blog/fatfs-bugs/	Third Party Advisory, Exploit
134c704f-9b21-4f2e-91b3-4a467353bcc0	https://github.com/runZeroInc/vulns-2026-fatfs-chance	Third Party Advisory, Exploit

Impacted products

	Vendor	Product	Version
	elm-chan	fatfs	*

JSON

To clipboard

{
  "affected": [
    {
      "affectedData": [
        {
          "defaultStatus": "unaffected",
          "product": "FatFs",
          "vendor": "ChaN",
          "versions": [
            {
              "lessThanOrEqual": "R0.16",
              "status": "affected",
              "version": "0",
              "versionType": "custom"
            }
          ]
        }
      ],
      "source": "44488dab-36db-4358-99f9-bc116477f914"
    }
  ],
  "configurations": [
    {
      "nodes": [
        {
          "cpeMatch": [
            {
              "criteria": "cpe:2.3:a:elm-chan:fatfs:*:*:*:*:*:*:*:*",
              "matchCriteriaId": "B99160BB-C4F5-4DA0-9FC9-0723E0633E00",
              "versionEndIncluding": "r0.16",
              "vulnerable": true
            }
          ],
          "negate": false,
          "operator": "OR"
        }
      ]
    }
  ],
  "cveTags": [],
  "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."
    }
  ],
  "id": "CVE-2026-6686",
  "lastModified": "2026-07-02T14:38:35.823",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "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"
        },
        "exploitabilityScore": 0.9,
        "impactScore": 3.6,
        "source": "44488dab-36db-4358-99f9-bc116477f914",
        "type": "Secondary"
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-6686",
          "options": [
            {
              "exploitation": "poc"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "role": "CISA Coordinator",
          "timestamp": "2026-07-01T15:05:23.138301Z",
          "version": "2.0.3"
        }
      }
    ]
  },
  "published": "2026-07-01T15:17:12.763",
  "references": [
    {
      "source": "44488dab-36db-4358-99f9-bc116477f914",
      "tags": [
        "Product"
      ],
      "url": "https://elm-chan.org/fsw/ff/"
    },
    {
      "source": "44488dab-36db-4358-99f9-bc116477f914",
      "tags": [
        "Third Party Advisory",
        "Exploit"
      ],
      "url": "https://github.com/runZeroInc/vulns-2026-fatfs-chance"
    },
    {
      "source": "44488dab-36db-4358-99f9-bc116477f914",
      "tags": [
        "Third Party Advisory"
      ],
      "url": "https://www.runzero.com/advisories/fatfs-uninit-cluster-exposure-cve-2026-6686/"
    },
    {
      "source": "44488dab-36db-4358-99f9-bc116477f914",
      "tags": [
        "Third Party Advisory",
        "Exploit"
      ],
      "url": "https://www.runzero.com/blog/fatfs-bugs/"
    },
    {
      "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
      "tags": [
        "Third Party Advisory",
        "Exploit"
      ],
      "url": "https://github.com/runZeroInc/vulns-2026-fatfs-chance"
    }
  ],
  "sourceIdentifier": "44488dab-36db-4358-99f9-bc116477f914",
  "vulnStatus": "Analyzed",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-908"
        }
      ],
      "source": "44488dab-36db-4358-99f9-bc116477f914",
      "type": "Secondary"
    }
  ]
}

CVE-2026-6686 (GCVE-0-2026-6686)

Vulnerability from cvelistv5 – Published: 2026-07-01 13:55 – Updated: 2026-07-01 15:05

Title

FatFs Use of Uninitialized Clusters After Seek Past EOF

Summary

Severity

4.6 (Medium)


                        
                          CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

SSVC

Exploitation: poc Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-07-01 15:05 UTC

CWE

CWE-908 - Use of uninitialized resource

Assigner

runZero icscert root

References

4 references

URL	Tags
https://www.runzero.com/blog/fatfs-bugs/	third-party-advisory
https://github.com/runZeroInc/vulns-2026-fatfs-chance	technical-description
https://elm-chan.org/fsw/ff/	product
https://www.runzero.com/advisories/fatfs-uninit-c…	third-party-advisory

Impacted products

1 product

Vendor	Product	Version
ChaN	FatFs	Affected: 0 , ≤ R0.16 (custom)

Date Public

2026-07-01 13:00

Credits

HD Moore of runZero, Inc. Tod Beardsley of runZero, Inc.

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-6686",
                "options": [
                  {
                    "Exploitation": "poc"
                  },
                  {
                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-07-01T15:05:23.138301Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-07-01T15:05:27.926Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "references": [
          {
            "tags": [
              "exploit"
            ],
            "url": "https://github.com/runZeroInc/vulns-2026-fatfs-chance"
          }
        ],
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "FatFs",
          "vendor": "ChaN",
          "versions": [
            {
              "lessThanOrEqual": "R0.16",
              "status": "affected",
              "version": "0",
              "versionType": "custom"
            }
          ]
        }
      ],
      "credits": [
        {
          "lang": "en",
          "type": "finder",
          "value": "HD Moore of runZero, Inc."
        },
        {
          "lang": "en",
          "type": "coordinator",
          "value": "Tod Beardsley of runZero, Inc."
        }
      ],
      "datePublic": "2026-07-01T13:00:00.000Z",
      "descriptions": [
        {
          "lang": "en",
          "supportingMedia": [
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              "type": "text/html",
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            }
          ],
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        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "attackComplexity": "LOW",
            "attackVector": "PHYSICAL",
            "availabilityImpact": "NONE",
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            "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"
          },
          "format": "CVSS",
          "scenarios": [
            {
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              "value": "GENERAL"
            }
          ]
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      ],
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          "tags": [
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          ],
          "url": "https://github.com/runZeroInc/vulns-2026-fatfs-chance"
        },
        {
          "tags": [
            "product"
          ],
          "url": "https://elm-chan.org/fsw/ff/"
        },
        {
          "tags": [
            "third-party-advisory"
          ],
          "url": "https://www.runzero.com/advisories/fatfs-uninit-cluster-exposure-cve-2026-6686/"
        }
      ],
      "source": {
        "discovery": "UNKNOWN"
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      "title": "FatFs Use of Uninitialized Clusters After Seek Past EOF",
      "x_generator": {
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  "cveMetadata": {
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    "dateReserved": "2026-04-20T15:06:22.242Z",
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}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.

Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.