CVE-2021-26855: Microsoft Exchange Server Remote Code Execution Vulnerability

Published Mar 2, 2021
·
Updated

Microsoft Exchange Server contains an unspecified vulnerability that allows for remote code execution. This vulnerability is part of the ProxyLogon exploit chain.

Other sources

Microsoft Exchange Server Remote Code Execution Vulnerability

NVD

Affected Software

25 affected components
Microsoft Exchange Server
Microsoft Exchange Server=2013-cumulative_update_21
Microsoft Exchange Server=2013-cumulative_update_22
Microsoft Exchange Server=2013-cumulative_update_23
Microsoft Exchange Server=2016-cumulative_update_10
Microsoft Exchange Server=2016-cumulative_update_11
Microsoft Exchange Server=2016-cumulative_update_12
Microsoft Exchange Server=2016-cumulative_update_13
Microsoft Exchange Server=2016-cumulative_update_14
Microsoft Exchange Server=2016-cumulative_update_15
Microsoft Exchange Server=2016-cumulative_update_16
Microsoft Exchange Server=2016-cumulative_update_17
Microsoft Exchange Server=2016-cumulative_update_18
Microsoft Exchange Server=2016-cumulative_update_19
Microsoft Exchange Server=2016-cumulative_update_8
Microsoft Exchange Server=2016-cumulative_update_9
Microsoft Exchange Server=2019
Microsoft Exchange Server=2019-cumulative_update_1
Microsoft Exchange Server=2019-cumulative_update_2
Microsoft Exchange Server=2019-cumulative_update_3
Microsoft Exchange Server=2019-cumulative_update_4
Microsoft Exchange Server=2019-cumulative_update_5
Microsoft Exchange Server=2019-cumulative_update_6
Microsoft Exchange Server=2019-cumulative_update_7
Microsoft Exchange Server=2019-cumulative_update_8

Event History

Mar 2, 2021
CVE Published
via MITRE·11:55 PM
Data Sourced
via MITRE·11:55 PM
DescriptionSeverity
Mar 3, 2021
Data Sourced
via NVD·12:15 AM
RemedyDescriptionSeverityWeaknessAffected Software
Nov 3, 2021
Known Exploited
via CISA·12:00 AM
Known Ransomware
via CISA·12:00 AM
Dec 2, 2023
News Published
06:54 PM
Oct 7, 2024
News Published
via BleepingComputer·02:51 PM
News Published
via BleepingComputer·02:52 PM
Nov 27, 2024
News Published
via The Register·11:44 PM
News Published
via The Register·11:48 PM
Jan 6, 2025
News Published
via BleepingComputer·02:54 PM
Jan 23, 2025
News Published
via The Register·11:30 PM
May 2, 2025
News Published
via BleepingComputer·02:32 PM
Apr 30, 2026
News Published
via The Register·11:00 AM

Peer vulnerabilities

Found alongside the following vulnerabilities.

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Frequently Asked Questions

1

What is CVE-2021-26855?

CVE-2021-26855 is a remote code execution vulnerability in Microsoft Exchange Server.

2

What is the severity of CVE-2021-26855?

The severity of CVE-2021-26855 is critical, with a severity value of 9.8.

3

Which products are affected by CVE-2021-26855?

Microsoft Exchange Server versions 2013, 2016, and 2019 are affected by CVE-2021-26855.

4

How do I fix CVE-2021-26855?

Update your Microsoft Exchange Server to the latest cumulative update to fix CVE-2021-26855.

5

Where can I find more information about CVE-2021-26855?

You can find more information about CVE-2021-26855 in the references provided: [CISA Emergency Directive 21-02](https://www.cisa.gov/emergency-directive-21-02), [Packet Storm Security](http://packetstormsecurity.com/files/161846/Microsoft-Exchange-2019-SSRF-Arbitrary-File-Write.html), [Packet Storm Security](http://packetstormsecurity.com/files/161938/Microsoft-Exchange-ProxyLogon-Remote-Code-Execution.html).

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