T1546.007 - Netsh Helper DLL

Adversaries may establish persistence by executing malicious content triggered by Netsh Helper DLLs. Netsh.exe (also referred to as Netshell) is a command-line scripting utility used to interact with the network configuration of a system. It contains functionality to add helper DLLs for extending functionality of the utility.(Citation: TechNet Netsh) The paths to registered netsh.exe helper DLLs are entered into the Windows Registry at HKLM\SOFTWARE\Microsoft\Netsh.

Adversaries can use netsh.exe helper DLLs to trigger execution of arbitrary code in a persistent manner. This execution would take place anytime netsh.exe is executed, which could happen automatically, with another persistence technique, or if other software (ex: VPN) is present on the system that executes netsh.exe as part of its normal functionality.(Citation: Github Netsh Helper CS Beacon)(Citation: Demaske Netsh Persistence)

Atomic Tests

Atomic Test #1 - Netsh Helper DLL Registration

You can register a “helper dll” with Netsh as a persistance mechanism. The code in the dll is executed every time netsh.exe is called. The NetshHelper.dll provided with the atomic will simply launch notepad when netsh.exe is run.

Blog Sample DLL code

Supported Platforms: windows

Elevation Required (e.g. root or admin)

Dependencies: Run with powershell!

Description: Helper DLL must exist on disk at specified location (#{helper_file})

Check Prereq Commands:

if (Test-Path "PathToAtomicsFolder\T1546.007\bin\NetshHelper.dll") { exit 0} else { exit 1}

Get Prereq Commands:

New-Item -Type Directory (split-path "PathToAtomicsFolder\T1546.007\bin\NetshHelper.dll") -ErrorAction ignore | Out-Null
Invoke-WebRequest "https://github.com/redcanaryco/atomic-red-team/raw/master/atomics/T1546.007/bin/NetshHelper.dll" -OutFile "PathToAtomicsFolder\T1546.007\bin\NetshHelper.dll"

Invoke-AtomicTest T1546.007 -TestNumbers 1 -GetPreReqs

Attack Commands: Run with command_prompt

netsh.exe add helper "PathToAtomicsFolder\T1546.007\bin\NetshHelper.dll"
taskkill /im notepad.exe /t /f > NUL 2>&1

Invoke-AtomicTest T1546.007 -TestNumbers 1

Cleanup:

netsh.exe delete helper "PathToAtomicsFolder\T1546.007\bin\NetshHelper.dll"

Invoke-AtomicTest T1546.007 -TestNumbers 1 -Cleanup

Detection

It is likely unusual for netsh.exe to have any child processes in most environments. Monitor process executions and investigate any child processes spawned by netsh.exe for malicious behavior. Monitor the HKLM\SOFTWARE\Microsoft\Netsh registry key for any new or suspicious entries that do not correlate with known system files or benign software.(Citation: Demaske Netsh Persistence)