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CVE-2021-25833

Status: ModifiedCritical (9.8)—

A file extension handling issue was found in [server] module of ONLYOFFICE DocumentServer v4.2.0.71-v5.6.0.21. The file extension is controlled by an attacker through the request data and leads to arbitrary file overwriting. Using this vulnerability, a remote attacker can obtain remote code execution on DocumentServer.

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).

Affected technologies (1)

Onlyoffice — Document Server

CWEs

References

Raw JSON (NVD)

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{
  "id": "CVE-2021-25833",
  "cveTags": [],
  "metrics": {
    "cvssMetricV2": [
      {
        "type": "Primary",
        "source": "nvd@nist.gov",
        "cvssData": {
          "version": "2.0",
          "baseScore": 7.5,
          "accessVector": "NETWORK",
          "vectorString": "AV:N/AC:L/Au:N/C:P/I:P/A:P",
          "authentication": "NONE",
          "integrityImpact": "PARTIAL",
          "accessComplexity": "LOW",
          "availabilityImpact": "PARTIAL",
          "confidentialityImpact": "PARTIAL"
        },
        "acInsufInfo": false,
        "impactScore": 6.4,
        "baseSeverity": "HIGH",
        "obtainAllPrivilege": false,
        "exploitabilityScore": 10,
        "obtainUserPrivilege": false,
        "obtainOtherPrivilege": false,
        "userInteractionRequired": false
      }
    ],
    "cvssMetricV31": [
      {
        "type": "Primary",
        "source": "nvd@nist.gov",
        "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": "cve@mitre.org",
      "affectedData": [
        {
          "vendor": "n/a",
          "product": "n/a",
          "versions": [
            {
              "status": "affected",
              "version": "n/a"
            }
          ]
        }
      ]
    }
  ],
  "published": "2021-03-01T16:15:14.510",
  "references": [
    {
      "url": "https://github.com/ONLYOFFICE/DocumentServer",
      "tags": [
        "Product",
        "Vendor Advisory"
      ],
      "source": "cve@mitre.org"
    },
    {
      "url": "https://github.com/ONLYOFFICE/server",
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      "source": "cve@mitre.org"
    },
    {
      "url": "https://github.com/ONLYOFFICE/server/blob/v5.6.0.21/DocService/sources/converterservice.js#L200",
      "tags": [
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      "source": "cve@mitre.org"
    },
    {
      "url": "https://github.com/ONLYOFFICE/server/blob/v5.6.0.21/FileConverter/sources/converter.js#L283",
      "tags": [
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      "source": "cve@mitre.org"
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    {
      "url": "https://github.com/ONLYOFFICE/server/blob/v5.6.0.21/FileConverter/sources/converter.js#L593",
      "tags": [
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      ],
      "source": "cve@mitre.org"
    },
    {
      "url": "https://github.com/merrychap/poc_exploits/tree/master/ONLYOFFICE/CVE-2021-25833",
      "tags": [
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      "source": "cve@mitre.org"
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    {
      "url": "https://github.com/ONLYOFFICE/DocumentServer",
      "tags": [
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    },
    {
      "url": "https://github.com/ONLYOFFICE/server/blob/v5.6.0.21/DocService/sources/converterservice.js#L200",
      "tags": [
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      "source": "af854a3a-2127-422b-91ae-364da2661108"
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    {
      "url": "https://github.com/ONLYOFFICE/server/blob/v5.6.0.21/FileConverter/sources/converter.js#L283",
      "tags": [
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      "source": "af854a3a-2127-422b-91ae-364da2661108"
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    {
      "url": "https://github.com/ONLYOFFICE/server/blob/v5.6.0.21/FileConverter/sources/converter.js#L593",
      "tags": [
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      "source": "af854a3a-2127-422b-91ae-364da2661108"
    },
    {
      "url": "https://github.com/merrychap/poc_exploits/tree/master/ONLYOFFICE/CVE-2021-25833",
      "tags": [
        "Exploit",
        "Third Party Advisory"
      ],
      "source": "af854a3a-2127-422b-91ae-364da2661108"
    }
  ],
  "vulnStatus": "Modified",
  "weaknesses": [
    {
      "type": "Primary",
      "source": "nvd@nist.gov",
      "description": [
        {
          "lang": "en",
          "value": "CWE-22"
        }
      ]
    }
  ],
  "descriptions": [
    {
      "lang": "en",
      "value": "A file extension handling issue was found in [server] module of ONLYOFFICE DocumentServer v4.2.0.71-v5.6.0.21. The file extension is controlled by an attacker through the request data and leads to arbitrary file overwriting. Using this vulnerability, a remote attacker can obtain remote code execution on DocumentServer."
    },
    {
      "lang": "es",
      "value": "Se encontró un problema de manejo de extensiones de archivo en el módulo [server] de ONLYOFFICE DocumentServer versiones v4.2.0.71-v5.6.0.21. La extensión del archivo está controlada por un atacante por medio de los datos de una petición y conlleva a una sobrescritura arbitraria del archivo. Con esta vulnerabilidad, un atacante remoto puede obtener una ejecución de código remota en DocumentServer"
    }
  ],
  "lastModified": "2026-06-17T03:42:29.673",
  "configurations": [
    {
      "nodes": [
        {
          "negate": false,
          "cpeMatch": [
            {
              "criteria": "cpe:2.3:a:onlyoffice:document_server:*:*:*:*:*:*:*:*",
              "vulnerable": true,
              "matchCriteriaId": "44FEDB54-DC75-4509-BBC1-1D2342FA95D0",
              "versionEndIncluding": "5.6.0.21",
              "versionStartIncluding": "4.2.0.71"
            }
          ],
          "operator": "OR"
        }
      ]
    }
  ],
  "sourceIdentifier": "cve@mitre.org"
}