Unlike the Medre AutoCAD worm discovered earlier this year, the Shenz Trojan is not interested in exfiltrating files to remote servers.
Instead, it creates a user account with administrative rights on the target OS, allowing attackers to plant additional malware and steal files in the future with minimal effort. It also creates network shares for all drives from C: through I:, and opens four ports on the system (137, 138, 139, and 445).
“These ports are associated with the Server Message Block (SMB) protocol, which provides access to files, printers, serial ports, and miscellaneous communications between nodes on a network running on Windows,” explains Trend Micro threat response engineer Anthony Joe Melgarejo.
“By opening the ports, exploits that target SMB can successfully run on affected systems, provided that the relevant vulnerabilities have not yet been patched.”
The malicious file carrying the Shenz Trojan sports a .FAS extension, a type of executable associated with macros that automate processes within AutoCAD.
“The primary advantage of AutoCAD malware may well be that users do not expect this type of document to be malicious,” Melgarejo points out, but adds that users should be careful about all document types and not just those that are “well-known” to contain malware.
It’s safe to say that the malware is targeting corporate computers - not many home users user AutoCAD privately. According to the researchers, this Trojan arrives on a system either as a file dropped by other malware or the users themselves download it unknowingly from malicious sites.