{
  "id": "CVE-2021-42321",
  "url": "https://spydr.io/cve/CVE-2021-42321",
  "published": "2021-11-10T01:19:50.047Z",
  "modified": "2026-08-19T19:23:07.277Z",
  "score": 8.8,
  "severity": "high",
  "cvss_version": "3.1",
  "vector": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
  "score_source": "microsoft.com",
  "epss": 0.91737,
  "epss_percentile": 0.99815,
  "exploited": true,
  "kev": {
    "added": "2021-11-17",
    "due": "2021-12-01",
    "action": "Apply updates per vendor instructions.",
    "ransomware": "Known",
    "name": "Microsoft Exchange Server Remote Code Execution Vulnerability",
    "notes": "https://nvd.nist.gov/vuln/detail/CVE-2021-42321"
  },
  "ssvc_exploitation": "active",
  "vendors": [
    "Microsoft"
  ],
  "products": [
    "Microsoft Exchange Server 2016 Cumulative Update 21",
    "Microsoft Exchange Server 2016 Cumulative Update 22",
    "Microsoft Exchange Server 2019 Cumulative Update 10",
    "Microsoft Exchange Server 2019 Cumulative Update 11"
  ],
  "cwes": [],
  "description": "Microsoft Exchange Server Remote Code Execution Vulnerability",
  "status": "Analyzed",
  "score_type": "Secondary",
  "scores": {
    "cvss_v40": null,
    "cvss_v31": 8.8,
    "cvss_v30": null
  },
  "references": [
    {
      "url": "https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-42321",
      "tags": [
        "Patch",
        "Vendor Advisory"
      ]
    },
    {
      "url": "http://packetstormsecurity.com/files/166153/Microsoft-Exchange-Server-Remote-Code-Execution.html",
      "tags": [
        "Exploit",
        "Third Party Advisory",
        "VDB Entry"
      ]
    },
    {
      "url": "http://packetstormsecurity.com/files/168131/Microsoft-Exchange-Server-ChainedSerializationBinder-Remote-Code-Execution.html",
      "tags": [
        "Exploit",
        "Third Party Advisory",
        "VDB Entry"
      ]
    },
    {
      "url": "https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-42321",
      "tags": [
        "Patch",
        "Vendor Advisory"
      ]
    },
    {
      "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-42321",
      "tags": [
        "US Government Resource"
      ]
    }
  ],
  "nvd_url": "https://nvd.nist.gov/vuln/detail/CVE-2021-42321",
  "covered_in": [],
  "attribution": [
    {
      "source": "NVD",
      "url": "https://nvd.nist.gov",
      "notice": "This product uses data from the NVD API but is not endorsed or certified by the NVD."
    },
    {
      "source": "CISA KEV",
      "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog",
      "notice": "Known exploited vulnerabilities from the CISA KEV catalog."
    },
    {
      "source": "FIRST EPSS",
      "url": "https://www.first.org/epss",
      "notice": "Exploit prediction scores from FIRST EPSS."
    }
  ]
}