CVE-2021-27078Network attack vector

Remote code execution through undisclosed server flaw

Published Mar 2, 2021 · Updated Aug 19, 2026

Remote code execution in affected Microsoft Exchange Server 2013, 2016, and 2019 builds allows remote authenticated users to run arbitrary code. Microsoft has not published the affected component or the operation that mishandles untrusted input. A network-reachable server and high privileges are required, but successful exploitation grants arbitrary code execution.

CVSS severity9.1
Critical
EPSS probability20.56%
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 affected Microsoft Exchange Server 2013, 2016, and 2019 builds allows remote authenticated users to run arbitrary code. Microsoft has not published the affected component or the operation that mishandles untrusted input. A network-reachable server and high privileges are required, but successful exploitation grants arbitrary code execution.

The record

CVE
CVE-2021-27078
Published
Mar 2, 2021
Updated
Aug 19, 2026
Vendor
Microsoft
Product
Microsoft Exchange Server 2016 Cumulative Update 18
Classifications
T1190
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

7.2NVDCVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H
9.1Microsoft CorporationCVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/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

T1190Exploit Public-Facing Application

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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