CVE-2021-31207 (GCVE-0-2021-31207)

Vulnerability from cvelistv5 – Published: 2021-05-11 19:11 – Updated: 2025-10-21 23:25
VLAI CISA KEV KEVintel KEV
Title
Microsoft Exchange Server Security Feature Bypass Vulnerability
Summary
Microsoft Exchange Server Security Feature Bypass Vulnerability
Severity
6.6 (Medium)
CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C
SSVC
Exploitation: active Automatable: no Technical Impact: total
CISA Coordinator (v2.0.3)
CWE
  • Defense in Depth
  • CWE-434 - Unrestricted Upload of File with Dangerous Type
Assigner
References
Impacted products
Vendor Product Version
Microsoft Microsoft Exchange Server 2013 Cumulative Update 23 Affected: 15.00.0 , < 15.00.1497.018 (custom)
    cpe:2.3:a:microsoft:exchange_server:2013:cumulative_update_23:*:*:*:*:*:*
 Create a notification for this product.
Microsoft Microsoft Exchange Server 2019 Cumulative Update 9 Affected: 15.02.0 , < 15.02.0858.012 (custom)
    cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_9:*:*:*:*:*:*
 Create a notification for this product.
Microsoft Microsoft Exchange Server 2016 Cumulative Update 20 Affected: 15.01.0 , < 15.01.2242.010 (custom)
    cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_20:*:*:*:*:*:*
 Create a notification for this product.
Microsoft Microsoft Exchange Server 2016 Cumulative Update 19 Affected: 15.01.0 , < 15.01.2176.014 (custom)
    cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_19:*:*:*:*:*:*
 Create a notification for this product.
Microsoft Microsoft Exchange Server 2019 Cumulative Update 8 Affected: 15.02.0 , < 15.02.0792.015 (custom)
    cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_8:*:*:*:*:*:*
 Create a notification for this product.
Date Public
2021-05-11 07:00
CISA KEV
Known Exploited Vulnerability - GCVE BCP-07 Compliant
KEV entry ID: ddc64a36-fa4b-44b6-aeed-22cf0b07b28e

Vulnerability ID: CVE-2021-31207

Status: Confirmed

Status Updated: 2021-11-03 00:00 UTC

Exploited: Yes

Timestamps
First Seen: 2021-11-03
Asserted: 2021-11-03
Scope
Notes: KEV entry: Microsoft Exchange Server Security Feature Bypass Vulnerability | Affected: Microsoft / Exchange Server | Description: Microsoft Exchange Server contains an unspecified vulnerability that allows for security feature bypass. | Required action: Apply updates per vendor instructions. | Due date: 2021-11-17 | Known ransomware campaign use (KEV): Known | Notes (KEV): https://nvd.nist.gov/vuln/detail/CVE-2021-31207
Evidence

Type: Vendor Report

Signal: Successful Exploitation

Confidence: 80%

Source: cisa-kev

Details
Cwes CWE-20 CWE-434
Feed CISA Known Exploited Vulnerabilities Catalog
Product Exchange Server
Due Date 2021-11-17
Date Added 2021-11-03
Vendorproject Microsoft
Vulnerabilityname Microsoft Exchange Server Security Feature Bypass 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
KEV entry ID: 3cbb3f39-d5ee-45e8-b7f2-eadac61a689c

Vulnerability ID: CVE-2021-31207

Status: Confirmed

Status Updated: 2021-11-03 00:00 UTC

Exploited: Yes

Timestamps
First Seen: 2021-11-03
Asserted: 2021-11-03
Scope
Notes: KEVIntel entry: Microsoft Exchange Server Security Feature Bypass Vulnerability | Affected: Microsoft / Microsoft Exchange Server 2013 Cumulative Update 23, Microsoft Exchange Server 2019 Cumulative Update 9, Microsoft Exchange Server 2016 Cumulative Update 20, Microsoft Exchange Server 2016 Cumulative Update 19, Microsoft Exchange Server 2019 Cumulative Update 8 | CVSS: 6.6 (MEDIUM) | 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 Security Feature Bypass Vulnerability
Vendor Microsoft
Product Microsoft Exchange Server 2013 Cumulative Update 23, Microsoft Exchange Server 2019 Cumulative Update 9, Microsoft Exchange Server 2016 Cumulative Update 20, Microsoft Exchange Server 2016 Cumulative Update 19, Microsoft Exchange Server 2019 Cumulative Update 8
Added Date 2021-11-03T00:00:00.000Z
Cvss Score 6.6
Epss Score None
Cvss Severity MEDIUM
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
To clipboard 

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    "vulnrichment": {
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      "cveMetadata": "{\"cveId\": \"CVE-2021-31207\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2025-10-21T23:25:45.697Z\", \"dateReserved\": \"2021-04-14T00:00:00.000Z\", \"assignerOrgId\": \"f38d906d-7342-40ea-92c1-6c4a2c6478c8\", \"datePublished\": \"2021-05-11T19:11:41.000Z\", \"assignerShortName\": \"microsoft\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.1"
    }
  }
}


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Tags
Taxonomy of the tags.





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.


Detection rules are retrieved from Rulezet.