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Security Operations · Advanced

Antimalware Scan Interface (AMSI)

A Windows interface that lets antimalware products scan script content and in-memory buffers at runtime.

Definition

AMSI passes PowerShell, VBScript, JScript, Office VBA and .NET content to the registered security product after deobfuscation, enabling detection of fileless threats. Attackers attempt AMSI bypasses by patching amsi.dll in memory, which itself is a detection opportunity.

Example

Defender blocking an obfuscated PowerShell script via AMSI before it runs.

Exam tip

AMSI bypass strings in logs are a strong indicator of malicious intent.

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