NetSh Helper DLL

Persistence, code execution using netsh helper arbitrary libraries.

Execution

NetshHelperBeacon helper DLL will be used to test out this technique. A compiled x64 DLL can be downloaded below:

43KB

NetshHelperBeacon.dll

NetshHelperBeacon

The helper library, once loaded, will start calc.exe:

attacker@victim

.\netsh.exe add helper C:\tools\NetshHelperBeacon.dll

Observations

Adding a new helper via commandline modifies registry, so as a defender you may want to monitor for registry changes in Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\NetSh:

When netsh is started, Procmon captures how InitHelperDLL expored function of our malicious DLL is called:

As usual, monitoring command line arguments is a good idea that may help uncover suspicious activity:

Interesting

Loading the malicious helper DLL crashed netsh. Inspecting the calc.exe process after the crash with Process Explorer reveals that the parent process is svchost, although the sysmon logs showed cmd.exe as its parent:

References

Event Triggered Execution: Netsh Helper DLL, Sub-technique T1546.007 - Enterprise | MITRE ATT&CK®