Microsoft's built-in antimalware solution does its best to prevent common attacks. Unfortunately for Windows 10 users, evading detection requires almost no effort at all. An attacker armed with this knowledge will easily bypass security software using any number of tools.
As Microsoft's antimalware solution is Windows 10's first line of defense, it's the subject of a lot of excellent security research. This article will provide a brief introduction to how attackers will evade it entirely.
What Is Antimalware Scan Interface (AMSI)?
The backbone of Microsoft's antimalware, introduced in Windows 10, is the Windows Antimalware Scan Interface, or AMSI. Antivirus applications, including Windows Defender, can call its set of APIs to request a scan for malicious software, scripts, and other content. To describe it briefly, let's look at Microsoft's definition:
The Windows Antimalware Scan Interface (AMSI) is a versatile interface standard that allows your applications and services to integrate with any antimalware product that's present on a machine. AMSI provides enhanced malware protection for your end-users and their data, applications, and workloads.
In the below screenshot, the attacker is downloading a script ("shell.ps1") containing nefarious code to invoke a connection to a remote server immediately. When attempting to execute PowerShell scripts in this ..
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