{
  "id": "CVE-2021-34473",
  "url": "https://spydr.io/cve/CVE-2021-34473",
  "published": "2021-07-14T18:15:11.163Z",
  "modified": "2026-08-10T19:58:52.800Z",
  "score": 9.1,
  "severity": "critical",
  "cvss_version": "3.1",
  "vector": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N",
  "score_source": "microsoft.com",
  "epss": 0.99999,
  "epss_percentile": 0.99996,
  "exploited": true,
  "kev": {
    "added": "2021-11-03",
    "due": "2021-11-17",
    "action": "Apply updates per vendor instructions.",
    "ransomware": "Known",
    "name": "Microsoft Exchange Server Remote Code Execution Vulnerability",
    "notes": "https://nvd.nist.gov/vuln/detail/CVE-2021-34473"
  },
  "ssvc_exploitation": "active",
  "vendors": [
    "Microsoft"
  ],
  "products": [
    "Microsoft Exchange Server 2013 Cumulative Update 23",
    "Microsoft Exchange Server 2016 Cumulative Update 19",
    "Microsoft Exchange Server 2016 Cumulative Update 20",
    "Microsoft Exchange Server 2019 Cumulative Update 8",
    "Microsoft Exchange Server 2019 Cumulative Update 9"
  ],
  "cwes": [
    "CWE-918"
  ],
  "description": "Microsoft Exchange Server Remote Code Execution Vulnerability",
  "status": "Analyzed",
  "score_type": "Secondary",
  "scores": {
    "cvss_v40": null,
    "cvss_v31": 9.1,
    "cvss_v30": null
  },
  "references": [
    {
      "url": "https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-34473",
      "tags": [
        "Patch",
        "Vendor Advisory"
      ]
    },
    {
      "url": "http://packetstormsecurity.com/files/163895/Microsoft-Exchange-ProxyShell-Remote-Code-Execution.html",
      "tags": [
        "Exploit",
        "Third Party Advisory",
        "VDB Entry"
      ]
    },
    {
      "url": "https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-34473",
      "tags": [
        "Patch",
        "Vendor Advisory"
      ]
    },
    {
      "url": "https://www.zerodayinitiative.com/advisories/ZDI-21-821/",
      "tags": [
        "Third Party Advisory",
        "VDB Entry"
      ]
    },
    {
      "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-34473",
      "tags": [
        "US Government Resource"
      ]
    }
  ],
  "nvd_url": "https://nvd.nist.gov/vuln/detail/CVE-2021-34473",
  "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."
    }
  ]
}