Remote code execution in Microsoft Exchange Server

Published: 2021-11-09 | Updated: 2022-01-06
Risk Critical
Patch available YES
Number of vulnerabilities 1
CVE-ID CVE-2021-42321
Exploitation vector Network
Public exploit This vulnerability is being exploited in the wild.
Vulnerable software
Microsoft Exchange Server
Server applications / Mail servers

Vendor Microsoft

Security Bulletin

This security bulletin contains one critical risk vulnerability.

1) Input validation error

EUVDB-ID: #VU58055

Risk: Critical

CVSSv3.1: 9.5 [CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H/E:H/RL:O/RC:C]

CVE-ID: CVE-2021-42321

CWE-ID: CWE-20 - Improper Input Validation

Exploit availability: Yes


The vulnerability allows a remote user to compromise the affected system.

The vulnerability exists due to insufficient validation of cmdlet arguments. A remote user can run a specially crafted cmdlet and execute arbitrary commands on the system.

Note, the vulnerability is being actively exploited in the wild.


Install updates from vendor's website.

Vulnerable software versions

Microsoft Exchange Server: 2016 - 2016 Cumulative Update 22, 2019 - 2019 Cumulative Update 11

CPE2.3 External links

Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote authenticated user via the Internet.

How the attacker can exploit this vulnerability?

The attacker would have to send a specially crafted request to the affected application in order to exploit this vulnerability.

Is there known malware, which exploits this vulnerability?

Yes. This vulnerability is being exploited in the wild.