PowerShell reflective in-memory .NET Assembly.Load execution
Detects the use of .NET reflection and assembly loading techniques within PowerShell or C# compiler (csc.exe) command lines. Attackers frequently use these methods to load malicious payloads directly into memory, bypassing disk-based detection mechanisms. The rule looks for the combination of reflection-related namespaces/methods and indicators of obfuscation or encoding such as Base64 strings, Gzip compression, and decryption routines.
Microsoft Sentinel (KQL)

