CISA Adds Two Web Shells to Exchange Server Guidance


Officials update mitigation steps to include two new Malware Analysis Reports identifying Web shells seen in Exchange Server attacks.

The Department of Homeland Security’s Cybersecurity and Infrastructure Security Agency (CISA) today updated its guidance for ongoing Microsoft Exchange Server exploits to include two new Malware Analysis Reports (MARs). 

Each of these reports, now included in CISA’s full “Mitigate Microsoft Exchange Server Vulnerabilities” alert, identifies a Web shell seen in post-compromised Microsoft Exchange servers. CISA has also updated seven existing MARs to include YARA rules developed by CISA to help organizations detect the malware seen so far in these attacks. 

All of the MARs shared so far focus on China Chopper, a Web shell commonly seen in the attacks. After exploiting an Exchange Server vulnerability to gain initial access, an attacker can use China Chopper to remotely execute operating system commands and conduct activities such as uploading and executing tools, pivoting to other systems, and exfiltrating data. 

Prior to today, CISA had already updated its guidance to detail seven China Chopper Web shells; today’s addition brings it to nine in total. Officials note this is not an all-inclusive list of the Web shells attackers are using. 


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