New Method that Involved With Defender Antivirus scanning process over SMB leads to Windows Defender Antivirus Bypass and allows any Malware to Run into Windows OS.
This FlowTricks Windows Defender, to Scan other Files or scans no files Instead of Scanning Malicious File when we Execute the Malicious file and Windows Load the Execution Process.
By using Custom-built SMB server, This Flow Bypass the Defender Scanning Process and Evade to Capture the Malicious File and Pass to OS for Execution.
According to Cyberark, This Attack calls it as an Illusion Gap and also This Attack Vector can Bypass the other Antivirus Products.
Windows Defender Antivirus Bypass
Initially, CyberArk Build a Custom SMB Server to Achieve this Goal by Serving Two Different files over SMB, one for Windows PE Loader and another for the Windows Defender Antivirus.
In This Case, Attack should Force Victim to execute an exploit hosted on the malicious SMB share.
Two File A and B which are Malicious and Benign that is used here to Process this Bypass Action against the Windows Defender.
According to Cyberark, When a process creation is made by Windows PE Loader, a request will be made to the SMB server for the executable file, and we will serve file A, which is malicious .
When Windows Defender requests the executed file, we will serve file B, which is benign. This way, file B will be scanned while file A will be executed.
Malicious File is Replaced by SMB Sever when Windows Defender Request to Scan the file which is Loaded into SMB Server by Windows PE Loader.
But SMB Server Proceed either serve a benign file or blocks the handle creation request Instead of Providing Malicious File Details.
CyberArk cyber research team leader Doron Naim Said, Once an attacker puts the malicious file into the share, the attacker can control which file to notify the Windows Defender that it will run.
So if the Attacker can able to Play by sitting from SMB Server Side, They can Address the Process Request whether the Request has made by OS or Windows Defender.
Once the attacker on the SMB side actually identifies that Windows Defender wants to read his file, they can hand it another benign file instead of the malicious file.
In This way, Defender will Only Scan the Benign File Instead of Malicious One and Finally Attacker can Bypass the Defender and Achieve the Goal.
Naim said this behavior is just the opposite and that even if Windows Defender is not able to scan a file, it would still allow the process to execute. CyberArk, meanwhile, said it has already privately disclosed similar issues to other security vendors.