PowerShell Remoting

One of the things I absolutely love about my job is being ~~thrown into the deep end of the rapids with little to no time to prepare~~ given the opportunity to try new things and new technologies, pushing me out of my comfort zone. It normally goes okay.

whitewater — actual camera footage of my last project

Case in point: a client of ours recently was investigating WinRM and whether or not it was secure, leading me down a rabbit hole of Certificates, Enterprise CA’s, SSL Handshakes, WireShark and more.

At the end of the initiative, I was asked to write up a summary to answer the question

Is WinRM secure or do I really need HTTPs too

In this post, I’ll talk us through my findings after days of research and testing, stepping through the default settings and some edge cases, hopefully covering the minimum you need to know in a short little post.

Authentication Security

Consider the following scenario: two computers, both members of the same domain. We run winrm quickconfig on both computers and don’t take any additional steps to lock things down. Is it secure? Are credentials or results passed in the clear? Until stated otherwise, assume HTTP until I mention it again.

From the very first communications and with no additional configuration, connections between the two computers will use Kerberos for initial authentication. If you’re not familiar with it, the bare minimum to know is that Kerberos is a trusted mechanism which ensures that credentials are strongly protected, and has a lot of nifty features like hashing and tickets which are used to ensure that raw credentials never go over the wire. So, domain joined computers do not pass creds in the clear. Continue reading →

the-case-of-the-ghost-certificate-p2

Oh boy, this has been a rollercoaster of emotions. But guys…we made it. We have finally, and definitively answered what happens to WinRM with HTTPs when certificates expire. If you’re curious about why this is a big question, see my previous posts on this topic.

Up until now, I’ve been able to say, conclusively, that WinRM generally seems to work, even as Certs expire and are renewed. But I’ve never known why: did WinRM automatically update the certs? Does Windows just not care about certs? What is the purpose of life?

Well, I can now shed light on at least some of those questions. I knew what I needed to do

Record a WireShark transfer and extract the certificate to tell definitively, which cert is being used to validate the session. Then we’ll know what happens.

Setting the stage

Two VMs, one domain. Server 2016 server, connected to from a Server 2012 R2 client. Newly created WinRM capable Certificate Template available to all domain members with a 4 hour expiration and 2 hour renewal period.

00-cert-temp

With the stage set, and the cert was present on both machines, I ran winrm quickconfig -transport:https on each, then made sure they could see each other, and remoted from one into the other. I recorded a WireShark trace of the remote session, uh remoting, then ran a command or two, then stopped recording. Then I opened the trace.

Continue reading →