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TI-2021-18752 Aliases CVE-2021-42321GHSA-3f87-66x4-f3p7

Microsoft Exchange Server Remote Code Execution Vulnerability

Priority CRITICAL 97Exploited in the wildPublished · Updated

Key facts

Attack vector
Network
Privileges required
Low
User interaction
None
Attack complexity
Low
Impact type
Code execution
Confidentiality · integrity · availability
High · High · High
Fix status
Fixed

Attack profile from CVSS 3.1 · CNA. Fix status from CNA and Microsoft. Impact type from Microsoft.

Summary

Microsoft Exchange Server Remote Code Execution Vulnerability

Why it matters now

Exploitation Active In CISA KEV since 2021-11-17CISA due date 2021-12-01Known ransomware use
EPSS 0.91737 99th percentileScored 2026-11-07
Public exploit Yes 2 exploit referencesTagged by NVD
Fix Fixed Microsoft: 1 update

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
Active
Automatable
No
Technical impact
Total

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
MicrosoftMicrosoft Exchange Server 2016 Cumulative Update 2115.01.0 to before 15.01.2308.02015.01.2308.020Patch availableCNA
MicrosoftMicrosoft Exchange Server 2016 Cumulative Update 2215.0.0 to before 15.01.2375.01715.01.2375.017Patch availableCNA
MicrosoftMicrosoft Exchange Server 2019 Cumulative Update 1015.02.0 to before 15.02.0792.01915.02.0792.019Patch availableCNA
MicrosoftMicrosoft Exchange Server 2019 Cumulative Update 1115.02.0 to before 15.02.0986.01415.02.0986.014Patch availableCNA
  • Microsoft Exchange Server 2016 Cumulative Update 21 VendorMicrosoft Affected 15.01.0 to before 15.01.2308.020 Fixed in 15.01.2308.020 Patch available CNA
  • Microsoft Exchange Server 2016 Cumulative Update 22 VendorMicrosoft Affected 15.0.0 to before 15.01.2375.017 Fixed in 15.01.2375.017 Patch available CNA
  • Microsoft Exchange Server 2019 Cumulative Update 10 VendorMicrosoft Affected 15.02.0 to before 15.02.0792.019 Fixed in 15.02.0792.019 Patch available CNA
  • Microsoft Exchange Server 2019 Cumulative Update 11 VendorMicrosoft Affected 15.02.0 to before 15.02.0986.014 Fixed in 15.02.0986.014 Patch available CNA

CPE configurations NVD · 4

CPEVersionsRoleVendor
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_21:*:*:*:*:*:*2016 cumulative_update_21VulnerableMicrosoft
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_22:*:*:*:*:*:*2016 cumulative_update_22VulnerableMicrosoft
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_10:*:*:*:*:*:*2019 cumulative_update_10VulnerableMicrosoft
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_11:*:*:*:*:*:*2019 cumulative_update_11VulnerableMicrosoft
  • cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_21:*:*:*:*:*:* Versions 2016 cumulative_update_21 Vulnerable ·Microsoft
  • cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_22:*:*:*:*:*:* Versions 2016 cumulative_update_22 Vulnerable ·Microsoft
  • cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_10:*:*:*:*:*:* Versions 2019 cumulative_update_10 Vulnerable ·Microsoft
  • cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_11:*:*:*:*:*:* Versions 2019 cumulative_update_11 Vulnerable ·Microsoft

Remediation

Microsoft 1 update

  • KB5007409
    Security Update
    • Microsoft Exchange Server 2013 Cumulative Update 23 15.00.1497.026
    • Microsoft Exchange Server 2016 Cumulative Update 21 15.01.2308.020
    • Microsoft Exchange Server 2016 Cumulative Update 22 15.01.2375.017
    • Microsoft Exchange Server 2019 Cumulative Update 10 15.02.0792.019
    • Microsoft Exchange Server 2019 Cumulative Update 11 15.02.0986.014

Vendor assessments

Microsoft

Microsoft's page for this CVE →

Impact
Remote Code Execution
Exploited
Yes
Publicly disclosed
No
Exploitability
Exploitation Detected

Timeline

  1. 2021-11-17 Added to CISA KEV
  2. 2026-10-02 Threatist record created from CVE-2021-42321
  3. 2026-10-03 Alias added: GHSA-3f87-66x4-f3p7

References

Exploit 2

Patch 2

  • TI-2024-14170 Microsoft Exchange Server Elevation of Privilege Vulnerability KEVCVSS 3.1CRITICAL 9.8
  • TI-2022-19610 Microsoft Exchange Server Elevation of Privilege Vulnerability KEVCVSS 3.1CRITICAL 9.8
  • TI-2021-13547 Microsoft Exchange Server Elevation of Privilege Vulnerability KEVCVSS 3.1CRITICAL 9.8
  • TI-2021-13502 Microsoft Exchange Server Remote Code Execution Vulnerability KEVCVSS 3.1CRITICAL 9.8
  • TI-2021-08465 Microsoft Exchange Server Remote Code Execution Vulnerability KEVCVSS 3.1CRITICAL 9.8
  • TI-2023-07929 Microsoft Exchange Server Remote Code Execution Vulnerability KEVCVSS 3.1HIGH 8.8
See all 258 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences