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CVE-2026-56857

Status: Awaiting AnalysisCritical (9.8)—

On Windows, when the target of Root.Mkdir or Root.MkdirAll is a junction pointing to an empty location, the operation can create a directory at the junction target even when that target is located outside the root. This only applies to operations where the last path component is a junction (path/to/junction, but not path/junction/target).

CVSS

Exploitation probability (EPSS)

EPSS (Exploit Prediction Scoring System, FIRST) estimates how likely a vulnerability is to be exploited in the wild within 30 days. It complements CVSS (impact) and CISA KEV (confirmed exploitation).

🎯 ATT&CK techniques

How this vulnerability is exploited and what the attacker gains, in MITRE ATT&CK terms.

Inferred by deterministic rules from the CVSS vector and CWE. Indicative only.

🛡️ ATT&CK mitigations that cover these techniques

Vulnerability ScanningPrivileged Account ManagementNetwork SegmentationLimit Access to Resource Over NetworkFilter Network TrafficApplication Isolation and Sandboxing

Affected technologies (1)

⚠ AI-inferred from the description — NVD hasn't analyzed this CVE yet, these aren't verified CPEs.

Golang — GOAI

CWEs

References

Raw JSON (NVD)

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{
  "id": "CVE-2026-56857",
  "cveTags": [],
  "metrics": {
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-56857",
          "role": "CISA Coordinator",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "yes"
            },
            {
              "technicalImpact": "total"
            }
          ],
          "version": "2.0.3",
          "timestamp": "2026-10-09T15:35:58.663117Z"
        }
      }
    ],
    "cvssMetricV31": [
      {
        "type": "Secondary",
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "cvssData": {
          "scope": "UNCHANGED",
          "version": "3.1",
          "baseScore": 9.8,
          "attackVector": "NETWORK",
          "baseSeverity": "CRITICAL",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
          "integrityImpact": "HIGH",
          "userInteraction": "NONE",
          "attackComplexity": "LOW",
          "availabilityImpact": "HIGH",
          "privilegesRequired": "NONE",
          "confidentialityImpact": "HIGH"
        },
        "impactScore": 5.9,
        "exploitabilityScore": 3.9
      }
    ]
  },
  "affected": [
    {
      "source": "security@golang.org",
      "affectedData": [
        {
          "vendor": "Go standard library",
          "product": "os",
          "versions": [
            {
              "status": "affected",
              "version": "0",
              "lessThan": "1.26.9",
              "versionType": "semver"
            },
            {
              "status": "affected",
              "version": "1.27.0-0",
              "lessThan": "1.27.2",
              "versionType": "semver"
            }
          ],
          "platforms": [
            "windows"
          ],
          "packageName": "os",
          "collectionURL": "https://pkg.go.dev",
          "defaultStatus": "unaffected",
          "programRoutines": [
            {
              "name": "Root.Mkdir"
            },
            {
              "name": "doInRoot"
            },
            {
              "name": "rootMkdirAll"
            },
            {
              "name": "Root.Chmod"
            },
            {
              "name": "Root.Chown"
            },
            {
              "name": "Root.Chtimes"
            },
            {
              "name": "Root.Lchown"
            },
            {
              "name": "Root.Link"
            },
            {
              "name": "Root.MkdirAll"
            },
            {
              "name": "Root.Remove"
            },
            {
              "name": "Root.RemoveAll"
            },
            {
              "name": "Root.Rename"
            },
            {
              "name": "Root.Symlink"
            }
          ]
        },
        {
          "vendor": "Go standard library",
          "product": "internal/syscall/windows",
          "versions": [
            {
              "status": "affected",
              "version": "0",
              "lessThan": "1.26.9",
              "versionType": "semver"
            },
            {
              "status": "affected",
              "version": "1.27.0-0",
              "lessThan": "1.27.2",
              "versionType": "semver"
            }
          ],
          "platforms": [
            "windows"
          ],
          "packageName": "internal/syscall/windows",
          "collectionURL": "https://pkg.go.dev",
          "defaultStatus": "unaffected",
          "programRoutines": [
            {
              "name": "Mkdirat"
            }
          ]
        }
      ]
    }
  ],
  "published": "2026-10-08T23:17:01.487",
  "references": [
    {
      "url": "https://go.dev/cl/847305",
      "source": "security@golang.org"
    },
    {
      "url": "https://go.dev/issue/81739",
      "source": "security@golang.org"
    },
    {
      "url": "https://groups.google.com/g/golang-announce/c/U2fTuyDJznI",
      "source": "security@golang.org"
    },
    {
      "url": "https://pkg.go.dev/vuln/GO-2026-6604",
      "source": "security@golang.org"
    }
  ],
  "vulnStatus": "Awaiting Analysis",
  "weaknesses": [
    {
      "type": "Secondary",
      "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
      "description": [
        {
          "lang": "en",
          "value": "CWE-1386"
        }
      ]
    }
  ],
  "descriptions": [
    {
      "lang": "en",
      "value": "On Windows, when the target of Root.Mkdir or Root.MkdirAll is a junction pointing to an empty location, the operation can create a directory at the junction target even when that target is located outside the root. This only applies to operations where the last path component is a junction (path/to/junction, but not path/junction/target)."
    }
  ],
  "lastModified": "2026-10-09T16:35:35.900",
  "sourceIdentifier": "security@golang.org"
}