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Potential AMSI Bypass Using NULL Bits

Sigma Rules

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Summary
This detection rule aims to identify attempts to bypass the Antimalware Scan Interface (AMSI) using specific strings and null byte manipulations in PowerShell commands. The AMSI provides a mechanism for applications to integrate antivirus solutions, thus enhancing their ability to detect threats. However, adversaries may attempt to obfuscate their payloads by introducing null characters that interfere with the normal parsing of commands. This rule detects command lines that contain patterns indicative of such bypass methods, specifically those featuring conditional statements in PowerShell that leverage null characters within the command execution flow. By identifying these artifacts, the detection mechanism enhances overall security posture against potential evasive tactics utilized by malware or malicious scripts.
Categories
  • Windows
  • Endpoint
Data Sources
  • Process
Created: 2023-01-04