#VU51169 Input validation error in Microsoft Exchange Server - CVE-2021-26858

Vulnerability identifier: #VU51169

Vulnerability risk: Critical

CVSSv4.0: 8.6 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:A/U:Red]

CVE-ID: CVE-2021-26858

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 attacker to execute arbitrary code on the system.

The vulnerability exists due to insufficient validation of user-supplied input. A remote attacker can send specially crafted data to the Exchange server and execute arbitrary code on the system.

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

Mitigation
Install updates from vendor's website.

Vulnerable software versions

Microsoft Exchange Server: 2013 Cumulative Update 2 15.00.0712.024 - 2013 RTM 15.00.0516.032, 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-2021-26858
https://msrc-blog.microsoft.com/2021/03/02/multiple-security-updates-released-for-exchange-server

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Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote non-authenticated attacker via the Internet.

Is there known malware, which exploits this vulnerability?

Yes. This vulnerability is being exploited in the wild.