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CVE-2021-26858

Microsoft Exchange Server Remote Code Execution Vulnerability

  • High 7.8
  • Exploited: added to CISA KEV 3 Nov 2021
  • Used in ransomware campaigns

Description

Microsoft Exchange Server Remote Code Execution Vulnerability

Key facts

Published
2 Mar 2021
Last changed
1 Oct 2026
Assigned by
microsoft
KEV added
3 Nov 2021
KEV fix due
3 May 2022
Used in ransomware
Yes, according to CISA
EPSS
93.651% likely to be exploited in the next 30 days, higher than 99.845% of CVEs (scores for 15 Nov 2026)
SSVC (CISA)
Exploitation: active; Automatable: yes; Technical impact: total

Severity scores

Each score is shown as its source gave it. They are not averaged or merged.

  • 7.8CVSS 3.1, Highfrom the CNA (microsoft)CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C

What to do

  • Apply updates per vendor instructions.CISA KEV required action

Historical context and remediation

This reference retains the original CVE publication date. A recent record update does not mean a new attack occurred.

No separately sourced impact summary is available on this page yet. Consult the description, version data and dated exploitation evidence.

Version statuses below come from the CNA. An “unaffected” version is not necessarily a currently supported release or proof of a patch date. EPSS is a dated risk estimate, not a count of historical attacks.

Read the original CVE record.

Affected products

VendorProductVersions
MicrosoftMicrosoft Exchange Server 2013 Cumulative Update 21
  • 15.00.0 up to but excluding 15.00.1395.012 (affected)
MicrosoftMicrosoft Exchange Server 2013 Cumulative Update 22
  • 15.00.0 up to but excluding 15.00.1473.006 (affected)
MicrosoftMicrosoft Exchange Server 2013 Cumulative Update 23
  • 15.00.0 up to but excluding 15.00.1497.012 (affected)
MicrosoftMicrosoft Exchange Server 2016 Cumulative Update 10
  • 15.01.0 up to but excluding 15.01.1531.012 (affected)
MicrosoftMicrosoft Exchange Server 2016 Cumulative Update 11
  • 15.01.0 up to but excluding 15.01.1591.018 (affected)
MicrosoftMicrosoft Exchange Server 2016 Cumulative Update 12
  • 15.01.0 up to but excluding 15.01.1713.010 (affected)
MicrosoftMicrosoft Exchange Server 2016 Cumulative Update 13
  • 15.01.0 up to but excluding 15.01.1779.008 (affected)
MicrosoftMicrosoft Exchange Server 2016 Cumulative Update 14
  • 15.01.0 up to but excluding 15.01.1847.012 (affected)
MicrosoftMicrosoft Exchange Server 2016 Cumulative Update 15
  • 15.01.0 up to but excluding 15.01.1913.012 (affected)
MicrosoftMicrosoft Exchange Server 2016 Cumulative Update 16
  • 15.01.0 up to but excluding 15.01.1979.008 (affected)
MicrosoftMicrosoft Exchange Server 2016 Cumulative Update 17
  • 15.01.0 up to but excluding 15.01.2044.013 (affected)
MicrosoftMicrosoft Exchange Server 2016 Cumulative Update 18
  • 15.01.0 up to but excluding 15.01.2106.013 (affected)
MicrosoftMicrosoft Exchange Server 2016 Cumulative Update 19
  • 15.01.0 up to but excluding 15.01.2176.009 (affected)
MicrosoftMicrosoft Exchange Server 2016 Cumulative Update 8
  • 15.01.0 up to but excluding 15.01.1415.010 (affected)
MicrosoftMicrosoft Exchange Server 2016 Cumulative Update 9
  • 15.01.0 up to but excluding 15.01.1466.016 (affected)
MicrosoftMicrosoft Exchange Server 2019
  • 15.02.0 up to but excluding 15.02.0221.018 (affected)
MicrosoftMicrosoft Exchange Server 2019 Cumulative Update 1
  • 15.02.0 up to but excluding 15.01.1979.006 (affected)
MicrosoftMicrosoft Exchange Server 2019 Cumulative Update 2
  • 15.02.0 up to but excluding 15.02.0397.011 (affected)
MicrosoftMicrosoft Exchange Server 2019 Cumulative Update 3
  • 15.02.0 up to but excluding 15.02.0464.015 (affected)
MicrosoftMicrosoft Exchange Server 2019 Cumulative Update 4
  • 15.02.0 up to but excluding 15.02.0659.012 (affected)
MicrosoftMicrosoft Exchange Server 2019 Cumulative Update 5
  • 15.02.0 up to but excluding 15.02.0595.008 (affected)
MicrosoftMicrosoft Exchange Server 2019 Cumulative Update 6
  • 15.02.0 up to but excluding 15.02.0529.013 (affected)
MicrosoftMicrosoft Exchange Server 2019 Cumulative Update 7
  • 15.02.0 up to but excluding 15.02.0721.013 (affected)
MicrosoftMicrosoft Exchange Server 2019 Cumulative Update 8
  • 15.02.0 up to but excluding 15.02.0792.010 (affected)

Timeline

  1. 2 Mar 2021 Published
  2. 3 Nov 2021 Added to the CISA KEV catalogue

References