Microsoft recently announced that they would be introducing SSH support in the coming Windows Server release. It has taken three attempts by the teams within Microsoft to gain the necessary approval to do this, and finally, third time is the charm. Hats off to those within Microsoft who have had the courage to keep to their guns with this one and get SSH included. You truly have made a positive improvement.

The introduction of SSH opens up a world of possibilities for administrators, developers and integrators; unfortunately, there seems to be quite a few in the industry that don’t share in the excitement. 

I think some people misunderstood why people were so excited. Some went so far as accusing a few of us of shouting “Death to Remoting”. I don’t see this as the death of Remoting, it is naïve to think that SSH will replace Remoting; SSH will compliment Remoting and solve a number of challenges which currently exist with Remoting.

Native support for SSH both as a client and as a server opens up a number of functions and tasks which until recently were only achievable via third party utilities, modules and just plain hacky code. Carlos Perez and I have both written PowerShell modules (his is better), that integrate with SSH, Posh-SSH and SSHFunctions respectively. We wrote these to bridge a number of gaps, gaps that will/should be removed with native SSH support. 

This is a new world for administrators and developers alike, be that those who work primarily in the Microsoft space, as well as those working with Linux.

Remoting –ne SSH –ne RDP

It should be painfully clear, but I want to make it absolutely crystal clear; Remoting does not equal SSH, SSH does not equal RDP and RDP does not equal Remoting.

Each of these protocols have a different aim:

• Remoting (or WinRM) is roughly a remote management protocol
• SSH provides a Secure Shell for text based management
• RDP provides remote GUI access for GUI management

We really shouldn’t get these confused, each of them have different goals and aims, and as administrators/developers you need to know each one, when each one is appropriate to use and when each one is inappropriate.

Remoting

Remoting is an implementation of the WS-Management, which is an open, SOAP based protocol for the management of things like servers, workstations, devices and applications. The WS-Management standard was developed by a bunch of smart people at AMD, DELL, Intel, Microsoft and Sun back in 2005.

Unfortunately, WS-Management didn’t really take off, with only 4 major implementations found on Wikipedia: Windows Remote Management (WinRM), an implementation in SUSE Linux Enterprise, a European research project and finally Intel’s Active Management Technology. It is easy to speculate why WS-Management didn’t take off, the most obvious is the heavy overheads of SOAP web services. SOAP was big back in the 2000s, it isn’t as popular now and with good reason.

Believe it or not, I like WS-Management and Remoting. Remoting supports two pieces of software to connect to each other, and efficiently exchange complex pieces of data, allowing administrators, developers and integrators to build rich pieces of software on top. 
Multifactor authentication is pretty limited with Remoting. While you can add two factor into RDP, remoting hasn’t had the same treatment. 

Server authentication in Remoting is typically a complex story. To start with, typical deployments will be based upon HTTP providing limited (read: no) authentication, if you want strong server authentication, then you need to switch to HTTPS. 

The switch to HTTPS for Remoting is where things start to fall apart. A typical Remoting HTTPS deployment will be based upon self-signed or internal PKI. If you stick with self-signed, you either need to manually trust each server’s certificate, or you can skip the CA trust checks. If you want proper certificates, typically you are going need to deploy a CA infrastructure, and then configure each server to use HTTPS; you can’t use Group Policy, it doesn’t support enabling HTTPS for Remoting. Finally, don’t turn off HTTP if you want to keep using the Windows Server Manager. If you want to understand how bad configuring HTTPS for Remoting is, check out the best guide available at Carlos’ Blog, WinRM SSL Certificate Deployment via GPO.

Remoting has unfortunately been missed when it goes for secure configuration guides, the same goes for things like IDS and IPS rules. Whilst there are obvious challenges for IDS/IPS scanning of Remoting traffic that is over HTTPS, thankfully we can apply a lot of the same policies and rules for IIS to Remoting.

I feel a little jaded by Microsoft’s release of a reference implementation of WS-Management for Linux. It should be obvious to Microsoft by now that big companies cannot force the open source community to implement the standards and solutions they want. I was kind of shocked to hear about this one.

Side note: How long till Remoting is RESTful?

SSH

SSH, or Secure Shell, is an encrypted protocol for the initiation of text-based shell sessions on remote machines and was originally developed to replace Telnet, RSH and REXEC. If you ask the average person what SSH is for, they will tell you it is what you manage Linux and Unix with.

Whilst it is possible to use SSH as an integration point into automation and management of remote endpoints, it doesn’t support the exchange of complex object types, it only supports strings. For those who haven’t tried using SSH for large amounts of remote command execution, the closest would be something like invoke-command. Don Jones explained it well, “It’s all text, all the way down to the turtles.” As he goes on to summarise, whilst text isn’t bad for automation, string manipulation isn’t good. I also feel that it is wise to point out that string manipulation is a great way to introduce security vulnerabilities as well.
SSH makes up for all of this, by being extremely secure. SSH supports multifactor authentication with support for both password and key authentication, something that Windows still hasn’t caught up to (natively). 

Server authentication, that is, the authentication of the server by the client (so we know we are connecting to the right server and we are not being MITM), is quite easy. Servers have a public and private key pair, we just need to verify the thumbprint of the public key, and then we can establish a trust relationship (from here to eternity if we so desire). 
Another advantage of SSH is we know extremely well what valid SSH traffic looks like. This is critical in protecting connections either leaving our networks perimeter or those entering from outside. If devices like our IPS and IDS systems know what a valid SSH packet looks like, then we can make an attempt to weed out the nefarious traffic.

Transferring files over SSH is extremely easy, fast and efficient. I have used SSH as a file transfer mechanism in a number of environments, be it at home, in financial institutions or even for backups and server migrations. In banking SSH is an industry standard, much like PGP/GPG for a reason.

In summary, SSH gives us a secure text session in a manner that is extremely easy and without a PKI, unfortunately it is pretty bad at the exchange of complex data.

Side note: Check out Mosh an SSH replacement (not available on Windows yet). I really like the idea’s behind Mosh and can’t wait to see where it goes. I would really love to see a synchronised state console like this one.

RDP

We should all by now, know what RDP is! RDP allows us to connect to remote devices and servers via a graphical session. RDP does remote graphical consoles really well, has a simple but quite reliable security model and supports some limited file transfer options.

RDP is a heavy protocol on a network connection and for obvious reasons. Even with the advances in later RDP protocol versions, sending a graphical interface over the Internet can still be slow and laggy; combine this with file transfers, and you are in for a long wait.
There are a number of ways to add multifactor authentication to RDP, most notably solutions from DuoSec. 

Server authentication in RDP is actually pretty good. RDP comes by default with a self-signed certificate which does provide a degree of server authentication. You can step it up a notch by moving up to certificates issued from an enterprise CA. Configuration of RDP to use an enterprise CA is extremely simple, you can use group policy all the way. For a great write up on how to set it up, check out Carlos’ post, RDP TLS Certificate Deployment Using GPO.

RDP has been around for a long while, and a significant number of IDS and IPS products have developed rules to detect malicious traffic. Much like SSH, there are plenty of secure configuration guides for RDP from a number of trusted sources.

We need to reduce our reliance on RDP, not just because of how slow it is when managing cloud based infrastructure but also because it doesn’t support automation to any extent. RDP will always exist, there are times when we will need to run a GUI on a remote machine. 

Enter-PSSession

Enter-PSSession deserves a special mention. Providing functionality much like SSH, Enter-PSSEssion allows users to initiate a text based shell session with a remote device all over Remoting. Yes, in many ways it does provide a similar functionality to SSH, but from personal experience it can be a bit slow and clunky. 

Why is Enter-PSSession a bit slow and clunky? Well the best way to understand why, is once again by Don <link>. With Enter-PSSession, keystrokes are not transmitted in real-time, instead, each whole line is transmitted, executed, and then the results sent back to us. With all of the SOAP overheads, you can start to see where things get bogged down.

The right tool for the right job

Different tasks require different tools. You don’t use a sledge hammer to drive a screw, you need a screwdriver.

If you are running a graphical interface directly on a server (for an application that doesn’t support running remotely), then you need RDP. If you have to run the GUI on the box, you don’t have any other option but to run the GUI on the box via an RDP session. Obviously, in this case, Remoting, SSH and Enter-PSSession aren’t going to be much help here.

Want to configure a server, well, then PowerShell with Remoting is probably your best tool. You could use a text based console session with SSH or Enter-PSSession, but that might be a bit too much. If you were working with say configuration files, maybe jumping to a full text session might be worthwhile.

The final situation is a complex but common one. You have a single server, maybe its hosted by a provider like Azure; your client doesn’t have any reason to trust that server, there isn’t a shared PKI to support server authentication. SSH in this situation will shine, chances are it will be easier and more secure. Either you are going to switch down to HTTP, trust a self-signed certificate or tell PowerShell to ignore CA validation errors. This is a great time for SSH to shine.

Side Note: It would be nice to see a PowerShell CMDLet to help verify Remoting certificates and even configure trust.

In each of these situations, a different remote management protocol was required. Where as in the past, we had to make do with three options (PowerShell with Remoting, Enter-PSSession, RDP) we have now gained a fourth (SSH).

A Whole New World…

I want to point to a post by Mattias Geniar, How SSH In Windows Server Completely Changes The Game. Mattias has put together an exceptional post on why SSH is a game changer in his mind.  

I feel that the introduction of SSH opens up more administration possibilities, there is an SSH client for Android, from that I could be managing my servers in minutes something that I can’t easily do that right now (well there is the PowerShell web page thing). 

The introduction of SSH also opens up opportunities for Windows in environments that are currently predominately OSX/Linux/Unix, which has to help in the adoption of products like Nano (but alas Nano will miss out this time round) and the IOT versions of Windows.

Remoting isn’t going to go away just because SSH support has been introduced. I wasn’t rejoicing the death of Remoting when SSH support was announced, I was rejoicing that progress is being made in cleaning up the whole landscape, starting with compatibility and trust. I have always seen Remoting as a successful failure, we have proved the idea works, now it is time to start working on something that is better. I really hope to see a more improved remote management protocol coming out from Microsoft over the coming years, something that is actually cross platform and easy to integrate. Until then, we have three exceptional management protocols in tool kit to use.

Kieran Jacobsen