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
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.
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!
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 :-/
SQL Saturday in Cleveland, Ohio is next week, on February 3rd. If you’re in the area or can easily make it there, I hope that you can come out for a great day of free SQL Server training. I enjoy presenting at SQL Saturdays; they’re fun and educational days for speakers and attendees, alike. Last time we were in Cleveland it had snowed overnight when it was time to leave town on Sunday morning. I’ve lived even longer in the south now, so if that happens again, it’ll be even more fun this time.
In addition to my session on Saturday, where I will talk about using database projects in SSDT/Visual Studio, I’ll also be presenting an all-day session Friday on Azure Infrastructure. Planning and designing your infrastructure is just as important in the cloud as it is when building new systems on-premises. As Azure continues to grow and expand around the world, more companies will be choosing to migrate (or deploy new) services to the public cloud. Understanding the underlying components is imperative to maximum-performance and highly-successful Azure deployments and hybrid migrations. In this session, we’ll cover infrastructure fundamentals with a bit of a focus on deploying and running SQL Server in Azure; however, there will be plenty of general background discussion that can be used for any workload.
We 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.
Except there is something out of the ordinary here. CU7 includes the patches for SQL Server related to the Spectre and Meltdown vulnerabilities (for more info on these as they relate to SQL Server, see Joey’s post here and Allen’s post here), and as a result, it is being flagged and published as a security update from Microsoft as KB 4058561.
Since this is a security update, that means it will be pushed down by/via Windows Update like other normal security patches. 4058561 says that, “This update will be provided via Microsoft Update at a future date”, but it’s probably safe to assume that this “future date” will be next Tuesday, January 9th, as that is the normal Patch Tuesday this month.
All that said, then, if you are or support a shop that likes to test their SQL CUs before they get deployed, if there aren’t also positive controls on what Windows Update does, it will be a good idea to start testing this update now. Sure, the Venn diagram of “people who test CUs” and “people who let Windows Update go to town on their SQL Servers, whether it be right off the bat Tuesday night or on the next weekend” probably don’t overlap much, but in case you fall into that category: Heads up.
Remember that CUs include all patches since their “baseline” (in this case, SP1), so you’re not going to just be getting the most recent updates–you’re going to be getting an additional six CUs’ worth, too.
Register for our webcast featuring Meagan Longoria, Kevin Kline and Denny Cherry as they explore how to make communications clearer, especially during these stressful situations by improving your report visualization techniques.
As Microsoft MVP’s and Partners as well as VMware experts, we are summoned by companies all over the world to fine-tune and problem-solve the most difficult architecture, infrastructure and network challenges.
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