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MediumSplunk security contentSteven Dick

PowerShell WebRequest Using Memory Stream

The following analytic detects the use of .NET classes in PowerShell to download a URL payload directly into memory, a common fileless malware staging technique. It leverages PowerShell Script Block Logging…

Description

The following analytic detects the use of .NET classes in PowerShell to download a URL payload directly into memory, a common fileless malware staging technique. It leverages PowerShell Script Block Logging (EventCode=4104) to identify suspicious PowerShell commands involving `system.net.webclient`, `system.net.webrequest`, and `IO.MemoryStream`. This activity is significant as it indicates potential fileless malware execution, which is harder to detect and can bypass traditional file-based defenses. If confirmed malicious, this technique could allow attackers to execute code in memory, evade detection, and maintain persistence in the environment.

Detection logic

Detection requirements

Platform
ESXiLinuxmacOSNetwork DevicesWindows

The rule states no platform. This is derived from the 3 ATT&CK techniques it maps to.

Log source category
powershell_script_block_logging_4104

Known benign triggers

  • No false positives have been identified at this time.

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