CVE-2021-31207

Status: AnalyzedMedium (6.6)⚠ Active exploitation

Microsoft Exchange Server Security Feature Bypass Vulnerability

CVSS

Version: 3.1
Vector: CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H
Base score: 6.6

Exploitation probability (EPSS)

Probability of exploitation in the next 30 days: 100%
Percentile among all scored CVEs: 100
Score date: 9/29/2026

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).

CISA KEV — actively exploited

Added to catalog: 11/3/2021
Remediation due date: 11/17/2021
Known ransomware use: Known

🎯 ATT&CK techniques

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

ExploitationT1210 Exploitation of Remote Serviceslateral movement85 %
Primary impactT1505.003 Web Shellpersistence80 %
Secondary impactT1059.001 PowerShellexecution75 %

AV:N sin privilegios iniciales en Exchange Server remoto (T1210). CWE-434 permite upload de archivos maliciosos que resultan en webshell (T1505.003) y ejecución de código (T1059.001). KEV activa por ransomware confirma explotación en cadenas de ataque reales.

Inferred by our analysis agent from the official description, CVSS vector and CWE, and checked by a supervisor. May contain errors.

🛡️ ATT&CK mitigations that cover these techniques

Disable or Remove Feature or Program Privileged Account Management Vulnerability Scanning User Account Management Threat Intelligence Program Network Segmentation

Affected technologies (1)

Microsoft — Exchange Server

CWEs

CWE-434
CWE-434

References

Raw JSON (NVD)

Show

{
  "id": "CVE-2021-31207",
  "cveTags": [],
  "metrics": {
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2021-31207",
          "role": "CISA Coordinator",
          "options": [
            {
              "exploitation": "active"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "total"
            }
          ],
          "version": "2.0.3",
          "timestamp": "2025-02-04T18:16:59.637651Z"
        }
      }
    ],
    "cvssMetricV2": [
      {
        "type": "Primary",
        "source": "nvd@nist.gov",
        "cvssData": {
          "version": "2.0",
          "baseScore": 6.5,
          "accessVector": "NETWORK",
          "vectorString": "AV:N/AC:L/Au:S/C:P/I:P/A:P",
          "authentication": "SINGLE",
          "integrityImpact": "PARTIAL",
          "accessComplexity": "LOW",
          "availabilityImpact": "PARTIAL",
          "confidentialityImpact": "PARTIAL"
        },
        "acInsufInfo": false,
        "impactScore": 6.4,
        "baseSeverity": "MEDIUM",
        "obtainAllPrivilege": false,
        "exploitabilityScore": 8,
        "obtainUserPrivilege": false,
        "obtainOtherPrivilege": false,
        "userInteractionRequired": false
      }
    ],
    "cvssMetricV31": [
      {
        "type": "Secondary",
        "source": "secure@microsoft.com",
        "cvssData": {
          "scope": "UNCHANGED",
          "version": "3.1",
          "baseScore": 6.6,
          "attackVector": "NETWORK",
          "baseSeverity": "MEDIUM",
          "vectorString": "CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H",
          "integrityImpact": "HIGH",
          "userInteraction": "NONE",
          "attackComplexity": "HIGH",
          "availabilityImpact": "HIGH",
          "privilegesRequired": "HIGH",
          "confidentialityImpact": "HIGH"
        },
        "impactScore": 5.9,
        "exploitabilityScore": 0.7
      },
      {
        "type": "Secondary",
        "source": "nvd@nist.gov",
        "cvssData": {
          "scope": "UNCHANGED",
          "version": "3.1",
          "baseScore": 6.6,
          "attackVector": "NETWORK",
          "baseSeverity": "MEDIUM",
          "vectorString": "CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H",
          "integrityImpact": "HIGH",
          "userInteraction": "NONE",
          "attackComplexity": "HIGH",
          "availabilityImpact": "HIGH",
          "privilegesRequired": "HIGH",
          "confidentialityImpact": "HIGH"
        },
        "impactScore": 5.9,
        "exploitabilityScore": 0.7
      }
    ]
  },
  "affected": [
    {
      "source": "secure@microsoft.com",
      "affectedData": [
        {
          "cpes": [
            "cpe:2.3:a:microsoft:exchange_server:2013:cumulative_update_23:*:*:*:*:*:*"
          ],
          "vendor": "Microsoft",
          "product": "Microsoft Exchange Server 2013 Cumulative Update 23",
          "versions": [
            {
              "status": "affected",
              "version": "15.00.0",
              "lessThan": "15.00.1497.018",
              "versionType": "custom"
            }
          ],
          "platforms": [
            "x64-based Systems"
          ]
        },
        {
          "cpes": [
            "cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_9:*:*:*:*:*:*"
          ],
          "vendor": "Microsoft",
          "product": "Microsoft Exchange Server 2019 Cumulative Update 9",
          "versions": [
            {
              "status": "affected",
              "version": "15.02.0",
              "lessThan": "15.02.0858.012",
              "versionType": "custom"
            }
          ],
          "platforms": [
            "x64-based Systems"
          ]
        },
        {
          "cpes": [
            "cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_20:*:*:*:*:*:*"
          ],
          "vendor": "Microsoft",
          "product": "Microsoft Exchange Server 2016 Cumulative Update 20",
          "versions": [
            {
              "status": "affected",
              "version": "15.01.0",
              "lessThan": "15.01.2242.010",
              "versionType": "custom"
            }
          ],
          "platforms": [
            "x64-based Systems"
          ]
        },
        {
          "cpes": [
            "cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_19:*:*:*:*:*:*"
          ],
          "vendor": "Microsoft",
          "product": "Microsoft Exchange Server 2016 Cumulative Update 19",
          "versions": [
            {
              "status": "affected",
              "version": "15.01.0",
              "lessThan": "15.01.2176.014",
              "versionType": "custom"
            }
          ],
          "platforms": [
            "x64-based Systems"
          ]
        },
        {
          "cpes": [
            "cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_8:*:*:*:*:*:*"
          ],
          "vendor": "Microsoft",
          "product": "Microsoft Exchange Server 2019 Cumulative Update 8",
          "versions": [
            {
              "status": "affected",
              "version": "15.02.0",
              "lessThan": "15.02.0792.015",
              "versionType": "custom"
            }
          ],
          "platforms": [
            "x64-based Systems"
          ]
        }
      ]
    }
  ],
  "published": "2021-05-11T19:15:10.397",
  "references": [
    {
      "url": "http://packetstormsecurity.com/files/163895/Microsoft-Exchange-ProxyShell-Remote-Code-Execution.html",
      "tags": [
        "Exploit",
        "Third Party Advisory",
        "VDB Entry"
      ],
      "source": "secure@microsoft.com"
    },
    {
      "url": "https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-31207",
      "tags": [
        "Patch",
        "Vendor Advisory"
      ],
      "source": "secure@microsoft.com"
    },
    {
      "url": "https://www.zerodayinitiative.com/advisories/ZDI-21-819/",
      "tags": [
        "Third Party Advisory",
        "VDB Entry"
      ],
      "source": "secure@microsoft.com"
    },
    {
      "url": "http://packetstormsecurity.com/files/163895/Microsoft-Exchange-ProxyShell-Remote-Code-Execution.html",
      "tags": [
        "Exploit",
        "Third Party Advisory",
        "VDB Entry"
      ],
      "source": "af854a3a-2127-422b-91ae-364da2661108"
    },
    {
      "url": "https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-31207",
      "tags": [
        "Patch",
        "Vendor Advisory"
      ],
      "source": "af854a3a-2127-422b-91ae-364da2661108"
    },
    {
      "url": "https://www.zerodayinitiative.com/advisories/ZDI-21-819/",
      "tags": [
        "Third Party Advisory",
        "VDB Entry"
      ],
      "source": "af854a3a-2127-422b-91ae-364da2661108"
    },
    {
      "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-31207",
      "tags": [
        "US Government Resource"
      ],
      "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0"
    }
  ],
  "vulnStatus": "Analyzed",
  "weaknesses": [
    {
      "type": "Primary",
      "source": "nvd@nist.gov",
      "description": [
        {
          "lang": "en",
          "value": "CWE-434"
        }
      ]
    },
    {
      "type": "Secondary",
      "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
      "description": [
        {
          "lang": "en",
          "value": "CWE-434"
        }
      ]
    }
  ],
  "descriptions": [
    {
      "lang": "en",
      "value": "Microsoft Exchange Server Security Feature Bypass Vulnerability"
    },
    {
      "lang": "es",
      "value": "Una vulnerabilidad de Omisión de la Característica de Seguridad de Microsoft Exchange Server"
    }
  ],
  "lastModified": "2026-06-17T03:51:27.123",
  "cisaActionDue": "2021-11-17",
  "cisaExploitAdd": "2021-11-03",
  "configurations": [
    {
      "nodes": [
        {
          "negate": false,
          "cpeMatch": [
            {
              "criteria": "cpe:2.3:a:microsoft:exchange_server:2013:cumulative_update_23:*:*:*:*:*:*",
              "vulnerable": true,
              "matchCriteriaId": "DA166F2A-D83B-4D50-AD0B-668D813E0585"
            },
            {
              "criteria": "cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_19:*:*:*:*:*:*",
              "vulnerable": true,
              "matchCriteriaId": "28FCA0E8-7D27-4746-9731-91B834CA3E64"
            },
            {
              "criteria": "cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_20:*:*:*:*:*:*",
              "vulnerable": true,
              "matchCriteriaId": "19C1EE0C-B8DD-4B91-BE4B-1C42D72FB718"
            },
            {
              "criteria": "cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_8:*:*:*:*:*:*",
              "vulnerable": true,
              "matchCriteriaId": "44ECF39A-1DE1-4870-A494-06A53494338D"
            },
            {
              "criteria": "cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_9:*:*:*:*:*:*",
              "vulnerable": true,
              "matchCriteriaId": "71CDF29B-116B-4DE2-AFD0-B62477FF0AEB"
            }
          ],
          "operator": "OR"
        }
      ]
    }
  ],
  "sourceIdentifier": "secure@microsoft.com",
  "cisaRequiredAction": "Apply updates per vendor instructions.",
  "cisaVulnerabilityName": "Microsoft Exchange Server Security Feature Bypass Vulnerability"
}