Microsoft Kinda, Sorta Broke RDP: That CredSSP RDP Error

Published On: 2018-05-16By:

If you’re running into this, it probably started on May Patch Tuesday, which was last week (the 8th). You are getting this error when you try to RDP to a/some servers:

An authentication error has occurred.

The function requested is not supported.

This could be due to CredSSP encryption oracle remediation.

Here’s what happened

An authentication error has occurred. The function requested is not supported. … This could be due to CredSSP encryption oracle remediation.

Errors make me sad

In March, a vulnerability in CredSSP (Credential Security Support Provider) was patched, which would affect authentication via RDP (this is outlined in advisory CVE-2018-0886).  However, it was implemented in such a way that the behavior change didn’t have to be “honored” by either the server or the client involved in an RDP session.

 

The intent was that this would be controlled by GPO in enterprise environments, and a new GPO setting to activate or deactivate this behavior was released at the same time.

GPO settings have a default value, which they will use when nothing has been explicitly set for a particular setting. In this case, the GPO has three possible values: Force Updated Clients (for servers to only take connections from patched clients), Mitigated (for both, and on a workstation means that it won’t fall back to old/insecure behavior when attaching to unpatched servers), and Vulnerable (for both, and means what it sounds like–anything goes!).

In March, the default behavior was set to “Vulnerable”, which means everything kept working for everyone. But in the May security rollup, the default setting for that GPO was flipped to “Mitigated” if there was not an explicit setting for it… end result being the core problem some are running into: Clients that have received the May update are no longer able to connect to RPD servers that have not received the March vulnerability fix.

Welp.

(For a bit more background on all of this, see this Microsoft blog post: https://blogs.technet.microsoft.com/askpfeplat/2018/05/07/credssp-rdp-and-raven/)

Good News: Easy Workaround

Fortunately, there’s an easy workaround that can be applied to any Windows workstation facing this behavior, with a couple caveats.

If you are getting the above error trying to RDP to a server, all you have to do is set the corresponding GPO on your local workstation to Vulnerable.

To set this, run “gpedit.msc” on your machine. When the Local Group Policy Editor launches, navigate to Computer Configuration\Administrative Templates\System\Credentials Delegation on the left side, and then find Encryption Oracle Remediation on the right. Open that up, flip it to Enabled, and then choose “Vulnerable” for Protection Level. Hit OK, close GPEdit & you’re done; the change will take effect immediately.

There are a couple caveats: First is, this means you’re choosing to operate in an unpatched situation, which I don’t recommend. The second is that you can only apply this GPO setting on your local workstation if you’re not in an AD environment where it’s been set at the domain level and it’s getting applied to your machine. If that’s the case, the AD-level GPO will stomp on your local setting if it’s different.

Again: This should only be a temporary measure. The real fix is to get the March updates on your servers so you can set your workstation back to at least Mitigated (really should be Force Updated Clients). It’s not going to be my fault if you leave things unpatched and in Vulnerable and then something bad happens!

Commentary

Some have been referring to this as a “bug” and…This isn’t a bug; I mean, the “breaking RDP” part isn’t a bug (the original vuln obviously is). This is 100% “system functions as designed.” There’s a vulnerability in a widely-used feature of Windows, and MS pulled the “better to be on the ground wishing you were in the air, than being in the air wishing you were on the ground” card here. Being a patch hard-liner (I saw too much shit in the early 2000s), I think this is fine. If you don’t like it, there’s a workaround. But, my attitude on this is tempered by the fact that it’s only listed as an “Important” update, and the exploitability seems a little bit out there. Maybe give us all a few more months to notice?

Regardless, I DO think there was a communication failure here, though. Since few people read patch notes on a regular basis (I don’t even, anymore), relying on those to get the message to people isn’t going to work. Even that PFE blog post–which is great–is still a little bit of shouting into the void until someone runs into the problem and goes looking for a solution.

I don’t know what to do about this part, because there’s really just not a mechanism to deal with it. And really, do we need another thing to watch for alerts and stuff? Plus, breaking changes happen on a regular basis… where do you draw the line? And what, should they have made the RDP client throw a pop-up message about this? That seems like an awful big hammer.

I guess I’m going to have to go back to reviewing KB articles for patches again :-/

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Let’s Talk About Group Managed Service Accounts

Published On: 2018-01-16By:

SQL Server service dialog, Log On tabWe all know the best practices for SQL Server service accounts–domain account (if you’re using Active Directory), non local admin, different one for each service (and server/instance), etc, etc. These are, of course, good best practices and they should be followed as closely as possible in Production and on servers/instances that house Production data.

A problem arises if you have more than just a couple-few servers or run some of the BI components, however. The number of service accounts involved in your SQL Server plant could be very large, necessitating an incredible amount of overhead when it comes to managing those accounts. This goes beyond simply creating and assigning them–chances are good that there are policies in place that require changing passwords. User accounts, service accounts, and other automation accounts likely all fall under this umbrella. If you’re lucky, maybe non-user accounts have a longer change interval, but it’s still something that is going to need to be done on a regular basis. In large environments, this could take an excruciatingly awful amount of time to do.

All of this is not to mention the human factor involved here. One of the recurring themes in a couple of my presentations is making an effort to automate as many things as possible to remove the human from the process. Not that we’re bad, but there are some things, especially tedious and repetitious tasks, where dumb things go wrong simply because of the nature of the work. Changing a bunch of service account passwords is definitely one of them. There used to be two types of sysadmins: those that have changed a service account’s password but forgot to update and restart the service itself, and those who will.

Enter Group Managed Service Accounts

Group Managed Service accounts (gMSAs) are a way to avoid most of the above work. They are special accounts that are created in Active Directory and can then be assigned as service accounts. They are completely managed by Active Directory, including their passwords. This means no more manual work to meet the password-changing policy–the machine takes care of that for you.

There are other security-related controls that can be gained with them, but this is the major feature.

I’ll also note that you–the DBA–are likely to need some help from your AD admin to get these set up. They’re going to need to actually create the accounts for you in the system, and there may be some changes needed to their AD configuration in order to support them. They’ll also need to have a Windows Server 2012 (or R2) domain controller in their domain, but I’d hope today that’s not going to be a hurdle to overcome.

Since I’m mostly here to talk about SQL Server, I’ll note a couple of different support situations. gMSAs are supported from SQL Server 2014 and on running on Windows Server 2012 R2 and on for everything you can do with SQL Server–standalone instances, Failover Clusters, Availability Groups. Just plain Managed Service Accounts (MSAs) can go back a little further, but they only support standalone instances of SQL Server.

From a non-SQL Server perspective, one of the major disadvantages of gMSAs is that one can’t just use them everywhere. Services have to be specifically designed to support the use of these accounts, and that’s not going to be the case everywhere.

Since this isn’t exactly a new feature, there’s plenty of documentation and blog posts out there to read about this feature and the various requirements to implement. There’s a great overview and setup blog post on MSDN here: https://blogs.msdn.microsoft.com/markweberblog/2016/05/25/group-managed-service-accounts-gmsa-and-sql-server-2016/

That post links to this old TechNet article, which still is a pretty good resource for understanding what these things are and a little more detail on what is going on in the back-end: https://technet.microsoft.com/en-us/library/hh831782.aspx

Finally, my coworker Joey has a slightly older writeup here, https://joeydantoni.com/2012/12/14/group-managed-service-accounts/, that walks through the process of setting this up. Note that some of the requirements have changed since that was written, but the general process remains the same.

gMSAs are a nice feature that aren’t too onerous to setup, but go a long way to make your life easier and your data far more secure.

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Surface Pro 3 i7 Users Be Aware Of The Power Usage

Published On: 2015-03-11By:

So recently I got myself a Surface Pro 3 with the i7 processor in it as my laptop. It works great, except for one little power issue that I’ve noticed. The i7 Surface Pro 3 uses a LOT of power when it’s plugged in. In fact it uses almost all the power that the power cable can provide. I know this because if you plug your phone into the USB port on the power brick your phone won’t charge.

When I had my phone (a Samsung S5) plugged in the phone kept showing that it was charging then not charging, then charging then not charging, over and over until I unplugged it.

Now I know this is a problem with the i7 Surface because my wife has the i5 and the same phone and can charge her phone with the Surface plugged in without issue.

Now truth be told I haven’t played with the power settings in Windows to see if that makes it go away, I simply plugged the phone into the USB port on the monitor and was done with it.  So there might be a way to slow down it’s charging so that you can charge a phone via the chargers USB port.  At some point I’ll probably figure out if that’s an option.

Denny

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Recommended reading from mrdenny for January 02, 2015

Published On: 2015-01-02By:

This week I’ve found some great things for you to read. These are a few of my favorites that I’ve found this week.

This weeks SQL Server person to follow on Twitter is: PASS_RM_Canada also known as PASS RM Canada

Hopefully you find these articles as useful as I did.

Don’t forget to follow me on Twitter where my username is @mrdenny.

Denny

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