PowerShell Assembly Loading via CL_LoadAssembly.ps1 Functions

ATT&CK techniques

Defense Evasion

Recon
Resource Dev
Initial Access
Execution
Persistence
Priv Esc
Defense Evasion
- T1216System Script Proxy Execution
Cred Access
Discovery
Lateral Movement
Collection
C2
Exfiltration
Impact

What it detects

This rule flags PowerShell process command lines that include calls to LoadAssemblyFromPath or LoadAssemblyFromNS associated with the CL_LoadAssembly.ps1 script. Attackers can use assembly loading to execute or access code from external libraries, potentially bypassing allowlisting controls such as AppLocker. It relies on process creation telemetry and matches command-line substrings indicating inline use of these functions.

Reporting behind it

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PowerShell Assembly Loading via CL_LoadAssembly.ps1 Functions

Pivot detection · T1216 · 9 related

Detection content is published as a reviewed draft. Tune thresholds and exclusions against your own telemetry before enabling this rule for alerting.

powershell-assembly-loading-via-cl-loadassembly-ps1-functions-c57872c7

title: PowerShell Assembly Loading via CL_LoadAssembly.ps1 Functions
id: 566da814-63a6-4467-adb5-7f528de6e218
status: test
description: This rule flags PowerShell process command lines that include calls to LoadAssemblyFromPath or LoadAssemblyFromNS associated with the CL_LoadAssembly.ps1 script. Attackers can use assembly loading to execute or access code from external libraries, potentially bypassing allowlisting controls such as AppLocker. It relies on process creation telemetry and matches command-line substrings indicating inline use of these functions.
references:
  - https://bohops.com/2018/01/07/executing-commands-and-bypassing-applocker-with-powershell-diagnostic-scripts/
  - https://lolbas-project.github.io/lolbas/Scripts/CL_LoadAssembly/
  - https://github.com/SigmaHQ/sigma/blob/master/rules/windows/process_creation/proc_creation_win_powershell_cl_loadassembly.yml
author: frack113, Nasreddine Bencherchali (Nextron Systems), Huntrule Team
date: 2022-05-21
modified: 2023-08-17
tags:
  - attack.stealth
  - attack.t1216
logsource:
  category: process_creation
  product: windows
detection:
  selection:
    CommandLine|contains:
      - "LoadAssemblyFromPath "
      - "LoadAssemblyFromNS "
  condition: selection
falsepositives:
  - Unknown
level: medium
license: DRL-1.1
related:
  - id: c57872c7-614f-4d7f-a40d-b78c8df2d30d
    type: derived

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