MS.Exchange.Server.ProxyRequestHandler.Remote.Code.Execution

Description

This indicates an attack attempt to exploit a Remote Code Execution in Microsoft Exchange Server.
The vulnerability is due to insufficient sanitization when handling a malicious request. A remote attacker may be able to exploit this to disclose data or execute arbitrary code within the context of the application, via a crafted HTTP request.

Outbreak Alert

Joint Cybersecurity Advisory (CSA) has released the top Common Vulnerabilities and Exposures (CVEs) used since 2020 by Peoples Republic of China (PRC) state-sponsored cyber actors as assessed by the National Security Agency (NSA), Cybersecurity and Infrastructure Security Agency (CISA), and Federal Bureau of Investigation (FBI). Previously, FortiGuard labs has already published various Outbreaks Alerts included in the released CISA's advisory such as: Apache Log4j, Hikvision Webserver Vulnerability, Atlassian Confluence OGNL RCE Vulnerability, Microsoft Exchange Server RCE Vulnerabilities etc. See the full list at: https://www.fortiguard.com/outbreak-alert Links to dedicated reports on each published outbreak by FortiGuard Labs are added to Additional Resources section below.

View the full Outbreak Alert Report

A suspected Iran-linked espionage group tracked as UNC1549 is actively targeting aerospace, defense, and telecommunications organizations across Europe and other regions. The threat actor employs a combination of highly tailored spear-phishing, credential theft from third-party services, and the abuse of virtual desktop infrastructure such as Citrix, VMware, and Azure VDI to gain initial access and move laterally within target networks.

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Firstly, if you are running an un-patched on-premise Microsoft Exchange version, you should upgrade immediately! This is a critical vulnerability that allows an attacker to access a desired user’s mailbox, requiring only the e-mail address of the user they wish to target! These details and more were disclosed by Volexity here. https://www.volexity.com/blog/2021/03/02/active-exploitation-of-microsoft-exchange-zero-day-vulnerabilities/ The vulnerabilities affect Exchange Server 2013, 2016 and 2019. Exchange Online is not affected.

View the full Outbreak Alert Report

Affected Products

Microsoft Exchange Server 2016 Cumulative Update 19
Microsoft Exchange Server 2019 Cumulative Update 8
Microsoft Exchange Server 2013 Cumulative Update 23
Microsoft Exchange Server 2019 Cumulative Update 7
Microsoft Exchange Server 2016 Cumulative Update 18

Impact

System Compromise: Remote attackers can gain control of vulnerable systems.

Recommended Actions

Apply the most recent upgrade or patch from the vendor.
https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26855