CVE-2021-26854Network attack vector

Remote code execution via undisclosed mechanism

Published Mar 2, 2021 · Updated Aug 19, 2026

Remote code execution in Microsoft Exchange Server 2013, 2016, and 2019 allows remote authenticated users to execute arbitrary code. Microsoft has not published the affected component or the operation that mishandles untrusted input. Exploitation requires network access, high privileges, and high attack complexity, and successful exploitation grants code execution on the server.

CVSS severity6.6
Medium
EPSS probability23.58%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Remote code execution in Microsoft Exchange Server 2013, 2016, and 2019 allows remote authenticated users to execute arbitrary code. Microsoft has not published the affected component or the operation that mishandles untrusted input. Exploitation requires network access, high privileges, and high attack complexity, and successful exploitation grants code execution on the server.

The record

CVE
CVE-2021-26854
Published
Mar 2, 2021
Updated
Aug 19, 2026
Vendor
Microsoft
Product
Microsoft Exchange Server 2016 Cumulative Update 18
Classifications
T1210
Attack vector
network
Privileges
admin

Timeline

How it unfolded

  1. Mar 2, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 19, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=15.01.0 <15.01.2106.013

What conditions does exploitation require?

Attack vectornetwork
Required privilegesadmin

What is affected?

Microsoft · Microsoft Exchange Server 2016 Cumulative Update 18version=15.01.0 <15.01.2106.013
Microsoft · Microsoft Exchange Server 2013 Cumulative Update 23version=15.00.0 <15.00.1497.012
Microsoft · Microsoft Exchange Server 2016 Cumulative Update 19version=15.01.0 <15.01.2176.009
Microsoft · Microsoft Exchange Server 2019 Cumulative Update 8version=15.02.0 <15.02.0792.010
Microsoft · Microsoft Exchange Server 2019 Cumulative Update 7version=15.02.0 <15.02.0721.013

Published CVSS scores

7.2NIST NVDCVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H
6.5NIST NVDAV:N/AC:L/Au:S/C:P/I:P/A:P
6.6Microsoft CorporationCVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesadmin
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1210Exploitation of Remote Services

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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