SessionManager backdoor first surfaced around Spring 2021, targeting Microsoft IIS Servers. The malware samples were first investigated only in early 2022.
The recently exposed backdoor has affected more than 20 governmental and non-governmental entities across Africa, South Asia, South America, the Middle East, and Europe. Security researchers speculate that some artifacts indicate that the attacks may be initiated by Gelsemium APT.
The backdoor exploits one of the ProxyLogon security holes in Exchange servers and disguises itself as a module for Internet Information Services (IIS), a web server application for Windows PCs.
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The detection rule above is aligned with the MITRE ATT&CK® framework v.10, addressing the Execution tactic represented by the User Execution (T1204) technique, and can be used across 25 SIEM, EDR, and XDR platforms.
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Coded in C++, SessionManager is a persistent initial access backdoor that enables attackers to manage files, run binaries from the server, drop malicious payloads, and access other endpoints in the compromised network while remaining undetected.
Once installed by IIS applications (required to handle the HTTP requests that are sent to the server), the SessionManager module processes HTTP requests from the hackers, executes the hidden instructions, and then passes them to the server to be processed like legitimate operations. According to the research data, the backdoor has been modified through numerous iterations, enhanced with sophisticated defensive evasion capabilities.
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