splApache-2.0from splunk/security_content

Powershell Processing Stream Of Data

The following analytic detects suspicious PowerShell script execution involving compressed stream data processing, identified via EventCode 4104. It leverages PowerShell Script Block Logging to flag scripts using `IO.Compression`, `IO.StreamReader`, or decompression methods. This activity is significant as it often indicates obfuscated PowerShell or embedded .NET/binary execution, which are common tactics for evading detection. If confirmed malicious, this behavior could allow attackers to execute hidden code, escalate privileges, or maintain persistence within the environment.

Quality

FP risk

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Rule sourcedetections/endpoint/powershell_processing_stream_of_data.yml

`powershell` EventCode=4104 ScriptBlockText = "*IO.Compression.*" OR ScriptBlockText = "*IO.StreamReader*" OR ScriptBlockText = "*]::Decompress*"
  | fillnull
  | stats count min(_time) as firstTime max(_time) as lastTime
    BY dest signature signature_id
       user_id vendor_product EventID
       Guid Opcode Name
       Path ProcessID ScriptBlockId
       ScriptBlockText
  | `security_content_ctime(firstTime)`
  | `security_content_ctime(lastTime)`
  | `powershell_processing_stream_of_data_filter`