#VU58055 Input validation error in Microsoft Exchange Server - CVE-2021-42321

Vulnerability identifier: #VU58055

Vulnerability risk: Critical

CVSSv4.0: 9.4 [CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H/E:A/U:Red]

CVE-ID: CVE-2021-42321

CWE-ID: CWE-20

Exploitation vector: Network

Exploit availability: Yes

Vulnerable software:
Microsoft Exchange Server
Server applications / Mail servers

Vendor: Microsoft

Description

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.

Mitigation
Install updates from vendor's website.

Vulnerable software versions

Microsoft Exchange Server: 2016 Cumulative Update 1 15.01.0396.030 - 2016 RTM 15.01.0225.042, 2019 Cumulative Update 1 15.02.0330.005 - 2019 RTM 15.02.0221.012

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External links
https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-42321
https://techcommunity.microsoft.com/t5/exchange-team-blog/released-november-2021-exchange-server-security-updates/ba-p/2933169

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Q & A

Can this vulnerability be exploited remotely?

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

Is there known malware, which exploits this vulnerability?

Yes. This vulnerability is being exploited in the wild.