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WinRM is my Remote Access Tool

July 22, 2015

One of my favorite blog posts last year was Adversary Tricks and Treats from CrowdStrike. In this post, CrowdStrike details the tradecraft of an actor they dub Deep Panda. In an attempt to skirt advanced malware hunting capability, Deep Panda leverages native tools to control target systems and spread laterally in a network. With the exception of their foothold, they don’t use malware to complete their objectives.

This is an important idea. One of my favorite red team tasks is to provide a credible adversary to exercise new ideas for network defense. There’s a positive shift away from the passive blinky boxes to the inquisitive analyst who has tools to ask questions at scale. As red operators, we have a neat opportunity to nurture and grow these analysts into formidable defenders.

All that future talk aside, it’s important to think about how to do this. One way I do it is by looking at different ways to operate. I think it’s important to have multiple concepts of offense and ways to simulate an on-going offensive operation. One of my favorite ways now is to play like Deep Panda and limit my use of malware as much as possible.

I’m keenly aware that skilled network defenders watch some assets more than they watch others. A domain controller is no-man’s land. A skilled team armed with techniques that don’t scale will watch their domain controller’s like hawks when they know a red team is exercising them. Workstations are… less important.

I like to live on the workstations with my malware and use native tools to interrogate and control servers as much as possible.

There are a lot of ways to abuse a trust relationship to run commands on a remote system. at, schtasks, sc, and wmic are among my favorites. I’m a WinRM fan too.

WinRM is the Windows Remote Management service. It listens on port 5985. It’s off by default, but some system administrators turn it on to enable easy remote management of their servers [hence the name, right?]

When WinRM is on, you can use PowerShell to remotely interrogate a server and control it. Or, if you’re feeling lucky, you can turn WinRM on yourself. Here’s how to enable WinRM via Beacon:

powershell Enable-PSRemoting -Force

The output will look like this:

winrm

WinRM does require a trust relationship with the target system. You’ll need a token for a domain user that is a local administrator to the target. You can steal one of these, make one with runas, or use Mimikatz to create a token to pass a password hash.

To control a target via WinRM from Beacon, here’s the syntax:

powershell InvokeCommand -ComputerName TARGET -ScriptBlock { dir c:\ }

PowerShell will run, via WinRM, whatever you specify inside of the script block. After this command completes, PowerShell will return the output to you.

The ability to run commands on a remote target AND get output back is nice. In most cases, this is enough capability to operate and achieve an objective. One of my favorite things though is the ability to run Mimikatz this way. PowerSploit’s Invoke-Mimikatz cmdlet allows you to specify a -ComputerName argument. Fun fact: this argument can be array of systems to run Mimikatz on. With this option specified, PowerSploit will run mimikatz via WinRM, in memory on the remote target, and report the output back to you.

Here’s the syntax to do it:

powershell-import /local/path/to/PowerSploit/Exfiltration/Invoke-Mimikatz.ps1
powershell Invoke-Mimikatz -ComputerName TARGET

Here’s a video of these concepts in action:

Between Mimikatz and the ability to run arbitrary commands remotely, I have a lot of operating capability right there. If you want to emulate a long-term embedded actor who does things a little differently, this is certainly a good TTP to try out.

2 comments

  1. So, the Cobalt Strike GUI got a facelift 🙂 It’s nice to see development going on…


    • Good eye. The video uses an unreleased version of Cobalt Strike 3.0. The 2.x series is still with us. As a vendor, I feel it’s important to have both the maintenance work (2.x) and the long-term strategic work (the “next big thing”). 3.0 is my next big iteration of Cobalt Strike. I can’t say much about it yet, but it’s close enough that my new videos will use and demonstrate it.



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