CVE-2021-42321 (GCVE-0-2021-42321)

Vulnerability from cvelistv5 – Published: 2021-11-10 00:47 – Updated: 2025-10-21 23:25
Title
Microsoft Exchange Server Remote Code Execution Vulnerability
Summary
Microsoft Exchange Server Remote Code Execution Vulnerability
SSVC
Exploitation: active Automatable: no Technical Impact: total
CISA Coordinator (v2.0.3)
CWE
Assigner
Impacted products
Vendor Product Version
Microsoft Microsoft Exchange Server 2016 Cumulative Update 21 Affected: 15.01.0 , < 15.01.2308.020 (custom)
    cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_21:*:*:*:*:*:*
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Microsoft Microsoft Exchange Server 2019 Cumulative Update 10 Affected: 15.02.0 , < 15.02.0792.019 (custom)
    cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_10:*:*:*:*:*:*
Create a notification for this product.
Microsoft Microsoft Exchange Server 2016 Cumulative Update 22 Affected: 15.0.0 , < 15.01.2375.017 (custom)
    cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_22:*:*:*:*:*:*
Create a notification for this product.
Microsoft Microsoft Exchange Server 2019 Cumulative Update 11 Affected: 15.02.0 , < 15.02.0986.014 (custom)
    cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_11:*:*:*:*:*:*
Create a notification for this product.
Date Public
2021-11-09 08:00
CISA KEV
Known Exploited Vulnerability - GCVE BCP-07 Compliant

Vulnerability ID: CVE-2021-42321

Status: Confirmed

Status Updated: 2021-11-17 00:00 UTC

Exploited: Yes


Timestamps
First Seen: 2021-11-17
Asserted: 2021-11-17

Scope
Notes: KEV entry: Microsoft Exchange Server Remote Code Execution Vulnerability | Affected: Microsoft / Exchange | Description: An authenticated attacker could leverage improper validation in cmdlet arguments within Microsoft Exchange and perform remote code execution. | Required action: Apply updates per vendor instructions. | Due date: 2021-12-01 | Known ransomware campaign use (KEV): Known | Notes (KEV): https://nvd.nist.gov/vuln/detail/CVE-2021-42321

Evidence

Type: Vendor Report

Signal: Successful Exploitation

Confidence: 80%

Source: cisa-kev


Details
Cwes CWE-184 CWE-502
Feed CISA Known Exploited Vulnerabilities Catalog
Product Exchange
Due Date 2021-12-01
Date Added 2021-11-17
Vendorproject Microsoft
Vulnerabilityname Microsoft Exchange Server Remote Code Execution Vulnerability
Knownransomwarecampaignuse Known

References

Created: 2026-02-02 12:28 UTC | Updated: 2026-02-06 07:17 UTC
KEVintel KEV
Known Exploited Vulnerability - GCVE BCP-07 Compliant

Vulnerability ID: CVE-2021-42321

Status: Confirmed

Status Updated: 2021-11-17 00:00 UTC

Exploited: Yes


Timestamps
First Seen: 2021-11-17
Asserted: 2021-11-17

Scope
Notes: KEVIntel entry: Microsoft Exchange Server Remote Code Execution Vulnerability | Affected: Microsoft / Microsoft Exchange Server 2016 Cumulative Update 21, Microsoft Exchange Server 2019 Cumulative Update 10, Microsoft Exchange Server 2016 Cumulative Update 22, Microsoft Exchange Server 2019 Cumulative Update 11 | CVSS: 8.8 (HIGH) | Used in malware: yes | Not yet in CISA KEV: False

Evidence

Type: Public Report

Signal: Confirmed Compromise

Confidence: 70%

Source: kevintel


Details
Feed KEVIntel (kevintel.com)
Title Microsoft Exchange Server Remote Code Execution Vulnerability
Vendor Microsoft
Product Microsoft Exchange Server 2016 Cumulative Update 21, Microsoft Exchange Server 2019 Cumulative Update 10, Microsoft Exchange Server 2016 Cumulative Update 22, Microsoft Exchange Server 2019 Cumulative Update 11
Added Date 2021-11-17T00:00:00.000Z
Cvss Score 8.8
Epss Score None
Cvss Severity HIGH
Epss Percentile None
Used In Malware yes
Ahead Of Cisa Kev None
Not Yet In Cisa Kev False

References

Created: 2026-06-19 12:47 UTC | Updated: 2026-06-19 12:47 UTC
Show details on NVD website

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      "containers": "{\"adp\": [{\"title\": \"CVE Program Container\", \"references\": [{\"url\": \"https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-42321\", \"tags\": [\"x_refsource_MISC\", \"x_transferred\"]}, {\"url\": \"http://packetstormsecurity.com/files/166153/Microsoft-Exchange-Server-Remote-Code-Execution.html\", \"tags\": [\"x_refsource_MISC\", \"x_transferred\"]}, {\"url\": \"http://packetstormsecurity.com/files/168131/Microsoft-Exchange-Server-ChainedSerializationBinder-Remote-Code-Execution.html\", \"tags\": [\"x_refsource_MISC\", \"x_transferred\"]}], \"providerMetadata\": {\"orgId\": \"af854a3a-2127-422b-91ae-364da2661108\", \"shortName\": \"CVE\", \"dateUpdated\": \"2024-08-04T03:30:38.363Z\"}}, {\"title\": \"CISA ADP Vulnrichment\", \"metrics\": [{\"other\": {\"type\": \"ssvc\", \"content\": {\"id\": \"CVE-2021-42321\", \"role\": \"CISA Coordinator\", \"options\": [{\"Exploitation\": \"active\"}, {\"Automatable\": \"no\"}, {\"Technical Impact\": \"total\"}], \"version\": \"2.0.3\", \"timestamp\": \"2024-01-03T16:43:32.753195Z\"}}}, {\"other\": {\"type\": \"kev\", \"content\": {\"dateAdded\": \"2021-11-17\", \"reference\": \"https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-42321\"}}}], \"timeline\": [{\"lang\": \"en\", \"time\": \"2021-11-17T00:00:00.000Z\", \"value\": \"CVE-2021-42321 added to CISA KEV\"}], \"references\": [{\"url\": \"https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-42321\", \"tags\": [\"government-resource\"]}], \"problemTypes\": [{\"descriptions\": [{\"lang\": \"en\", \"type\": \"CWE\", \"description\": \"CWE-noinfo Not enough information\"}]}], \"providerMetadata\": {\"orgId\": \"134c704f-9b21-4f2e-91b3-4a467353bcc0\", \"shortName\": \"CISA-ADP\", \"dateUpdated\": \"2025-02-04T19:04:59.268Z\"}}], \"cna\": {\"title\": \"Microsoft Exchange Server Remote Code Execution Vulnerability\", \"metrics\": [{\"format\": \"CVSS\", \"cvssV3_1\": {\"version\": \"3.1\", \"baseScore\": 8.8, \"baseSeverity\": \"HIGH\", \"vectorString\": \"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C\"}, \"scenarios\": [{\"lang\": \"en-US\", \"value\": \"GENERAL\"}]}], \"affected\": [{\"cpes\": [\"cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_21:*:*:*:*:*:*\"], \"vendor\": \"Microsoft\", \"product\": \"Microsoft Exchange Server 2016 Cumulative Update 21\", \"versions\": [{\"status\": \"affected\", \"version\": \"15.01.0\", \"lessThan\": \"15.01.2308.020\", \"versionType\": \"custom\"}], \"platforms\": [\"x64-based Systems\"]}, {\"cpes\": [\"cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_10:*:*:*:*:*:*\"], \"vendor\": \"Microsoft\", \"product\": \"Microsoft Exchange Server 2019 Cumulative Update 10\", \"versions\": [{\"status\": \"affected\", \"version\": \"15.02.0\", \"lessThan\": \"15.02.0792.019\", \"versionType\": \"custom\"}], \"platforms\": [\"x64-based Systems\"]}, {\"cpes\": [\"cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_22:*:*:*:*:*:*\"], \"vendor\": \"Microsoft\", \"product\": \"Microsoft Exchange Server 2016 Cumulative Update 22\", \"versions\": [{\"status\": \"affected\", \"version\": \"15.0.0\", \"lessThan\": \"15.01.2375.017\", \"versionType\": \"custom\"}], \"platforms\": [\"x64-based Systems\"]}, {\"cpes\": [\"cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_11:*:*:*:*:*:*\"], \"vendor\": \"Microsoft\", \"product\": \"Microsoft Exchange Server 2019 Cumulative Update 11\", \"versions\": [{\"status\": \"affected\", \"version\": \"15.02.0\", \"lessThan\": \"15.02.0986.014\", \"versionType\": \"custom\"}], \"platforms\": [\"x64-based Systems\"]}], \"datePublic\": \"2021-11-09T08:00:00.000Z\", \"references\": [{\"url\": \"https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-42321\", \"tags\": [\"x_refsource_MISC\"]}, {\"url\": \"http://packetstormsecurity.com/files/166153/Microsoft-Exchange-Server-Remote-Code-Execution.html\", \"tags\": [\"x_refsource_MISC\"]}, {\"url\": \"http://packetstormsecurity.com/files/168131/Microsoft-Exchange-Server-ChainedSerializationBinder-Remote-Code-Execution.html\", \"tags\": [\"x_refsource_MISC\"]}], \"descriptions\": [{\"lang\": \"en-US\", \"value\": \"Microsoft Exchange Server Remote Code Execution Vulnerability\"}], \"problemTypes\": [{\"descriptions\": [{\"lang\": \"en-US\", \"type\": \"Impact\", \"description\": \"Remote Code Execution\"}]}], \"providerMetadata\": {\"orgId\": \"f38d906d-7342-40ea-92c1-6c4a2c6478c8\", \"shortName\": \"microsoft\", \"dateUpdated\": \"2024-05-29T14:47:48.107Z\"}}}",
      "cveMetadata": "{\"cveId\": \"CVE-2021-42321\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2025-10-21T23:25:25.274Z\", \"dateReserved\": \"2021-10-12T00:00:00.000Z\", \"assignerOrgId\": \"f38d906d-7342-40ea-92c1-6c4a2c6478c8\", \"datePublished\": \"2021-11-10T00:47:43.000Z\", \"assignerShortName\": \"microsoft\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.1"
    }
  }
}


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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

Author Source Type Date Other

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

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Detection rules are retrieved from Rulezet.

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