Markus Lassfolk – Page 9

Howto get NAP with Server and Domain Isolation to play together

If you are trying to get NAP (Network Access Protection) and SDI (Server & Domain Isolation) to play nice, you might not get the results you are expecting. I’m going to explain howto get NAP with Server and Domain Isolation to play together

There are plenty of Blogs and Guides out there, explaining how to get either NAP or Server and/or Domain Isolation to work. And that’s basically no problem so I won’t cover that here today.
But I’ve so far not found anyone who’s tried to combine both technologies.

Background

First of all, some background for my environment. I’m working on a project where we want to implement NAP to get the health check, but also Server and Domain Isolation to make sure that only trusted clients and users can talk to the systems they have access to. There was no doubt that we would use Certificates to validate the client health state.

Two Windows Server 2008 R2 Servers with HRA/NAP Roles and the Stand-Alone CA Role were installed for redundancy. Clients are getting the Health Certificates and all is good. The SA (Security Associations) policy on the servers and clients is configured to “Require Inbound and Request Outbound Authentication”, with a requirement for a Health Certificate from the organizations CA Servers. So far, so good.

The clients can now access the server when they have a valid health state, and are unable to access the server if they don’t. Yay! NAP works.

And the nice thing is that since the HRA only serves Domain Joined clients. As the servers won’t talk to any client without a Health Certificate, and only Domain Joined client can get one, we have also got “Domain Isolation”. Ok, two out of three check boxes done.

Now, try to use Server Isolation and configure a Firewall Rule to only allow ClientA to talk to connect to ServerX via RDP. That does not work. Well, it does work to create the rule, but it will never allow the traffic.
The reason is that when you use a NAP Certificate to authenticate the connection, there is no mapping to the computer account. Which makes it impossible to use a Computer Based rule.

Notice “No Authentication”.

Okay, so if you use the check box “Enable certificate to account mapping”?

Sorry, that doesn’t work either. When you use the Health Certificate feature, no certificate mapping is done in the Windows Firewall. This has been verified in the Windows source code.

This blog post does state that it should be possible to use that check box and then use a Policy “Access this computer from the network” where you can specify which computers are able to access the server over the network. But it’s still “All or nothing”. You can’t specify that ClientA should be able to access the SQL Server but nothing else.

Solution for NAP with Server and Domain Isolation

Luckily, there is a kind of workaround. To be honest, it’s not that common that you want to restrict so only ClientA, ClientB and ClientC can access the SQL Service on ServerX. I would dare to say its more common that you want to restrict which Users can access the service. Right?

I want to control so UserD, UserE and userF can access the RDP (Remote Desktop) Service, from any Health Domain Joined Client. It doesn’t really matter which client they connect from as long as it’s healthy and domain joined. Or I could control which clients they are able to logon to.

So by using a “Secondary Authentication” option, where we Authenticate the User, like this.
Still the same options for the Computer Authentication. Just add a Secondary Authentication on the SA for User (Kerberos v5). It’s then possible to restrict which users are able to connect to a specific service.

In your firewall RDP Rule, configure it to Require a secure connection, and specify which users should be able to access the service. Now try to connect with two different users via RDP. You should see how the rule is applied and works.

I decided to create a Firewall Rule for RDP that only allowed “TestUser” to connect to the service.
In the screenshot below, the upper RDP is started with the TestUser Account, while the bottom RDP Client is started with “Runas Domain\Administrator” which according to the rule, should not be allowed to connect. And as you see, it’s not able to connect, which is expected.

Summary

To get NAP to work with Server Isolation, you have to enable “Second Authentication” for the User with Kerberos Authentication, so there is Authentication done when the connection is established. Which in turn makes it possible to create Firewall Rules that can be applied to User Object, unfortunately not to computer objects.

How to launch programs from the Windows Logon screen

It does happen from time to time, that I want to start some troubleshooting tools before a user logs on to the system. For example Sysinternals Process Monitor or xperf / wpr etc.

There are several ways to do it, as with most things with IT. You can either logon with another user, start the tools and then use Fast User Switching.
Or enable Boot Logging to get the full boot sequence + logon for a user.
Or use Psexec from a remote system, etc etc
Another way to do it, is to execute any tool of your choice from the Windows logon (winlogon) screen. The nice side effect is that you will be executing the tool as System, with full permissions.

I recently had to troubleshoot a “Password Reset” solution, which launches a browser from the Logon screen and it were unable to connect to the web-service. If you ran it from within windows as a normal user account, or system account, it worked. So I had to troubleshoot the problem as it was happening.

Logon as a local administrator
Make a copy of %windir%\system32\utilman.exe
Take ownership of %windir%\system32\utilman.exe
Grant yourself full control permission on the file.
Replace utilman.exe with cmd.exe (or any other tool of your choise, though CMD is good as you can execute other tools from that one).
At the windows logon screen press the “Accessibility icon” in the bottom left corner.
Wahoo, you now have a command prompt with System Access

This works on Vista, Windows 7 and Windows 8.

List computer certificates that will expire with Powershell

Just a small simple script that will list all Computer Cerificates that will expire in 90 days, to give you a heads up and time to renew them.

To list computer certificates that will expire in 90 days:

# Show computer certificates that will expire in 90 days 
get-childitem cert:LocalMachine\My -recurse | where-object {$_.NotAfter -gt (get-date)} | select Subject,FriendlyName,Thumbprint,@{Name="Expires in (Days)";Expression={($_.NotAfter).subtract([DateTime]::Now).days}} | where "Expires in (Days)" -lt 90 | Sort "Expires in (Days)"

# Show computer certificates that will expire in 90 days

get-childitem cert:LocalMachine\My -recurse | where-object {$_.NotAfter -gt (get-date)} | select Subject,FriendlyName,Thumbprint,@{Name="Expires in (Days)";Expression={($_.NotAfter).subtract([DateTime]::Now).days}} | where "Expires in (Days)" -lt 90 | Sort "Expires in (Days)"

Just change “-lt 90” to some other value to adjust the expiry period.

List all Unsigned Drivers with Powershell

I had a need for getting all Unsigned drivers in a Windows 8 system to help out with some debugging.

# List all unsigned Drivers in the system  
$SysFiles = driverquery /si /FO CSV | ConvertFrom-CSV | 
    Where-Object -Property IsSigned -EQ "FALSE" | 
    Select-Object -Property InfName | 
    Where-Object { $_.InfName -like "*.inf" } | 
    foreach 
    { 
      Select-String -Path $env:SystemRoot\inf\$($_.InfName) -Pattern ServiceBinary | 
      select-string -Pattern \.SYS 
    } 
$UnSigned = $SysFiles.Line -replace ".*\\" | select -Unique

# List all unsigned Drivers in the system

$SysFiles = driverquery /si /FO CSV | ConvertFrom-CSV |

Where-Object -Property IsSigned -EQ "FALSE" |

Select-Object -Property InfName |

Where-Object { $_.InfName -like "*.inf" } |

foreach

{

Select-String -Path $env:SystemRoot\inf\$($_.InfName) -Pattern ServiceBinary |

select-string -Pattern \.SYS

}

$UnSigned = $SysFiles.Line -replace ".*\\" | select -Unique

As I’m still learning Powershell there might be better and faster ways of solving this problem, but this seems to work good enough for me, and hopefully for you too.

It’s a quite straight forward and easy script to use and change if there is a need, such as instead of showing Unsigned drivers, list all Signed Drivers by using IsSigned -EQ “TRUE”.
Use driverquery.exe to list all Unsigned Drivers to CSV, then import that CSV into Powershell and display all Drivers that’s unsigned (-EQUAL “False”). You will actually just get the .INF file at this point which kind of sucks, not the driverfile which we need in this case.
So for each returned .INF file, we are then opening those files in c:\windows\INF (that’s where Windows stores all installed INF/diver files) and find all .SYS files (drivers) referenced in the INF files. And after some more filtering, it then outputs a list of the unsigned drivers ($UnSigned), like this.

PS C:> $UnSigned VClone.sys nvhda32.sys nvhda64.sys nvhda32v.sys nvhda64v.sys PS C:> — PS C:> $UnSigned
VClone.sys
nvhda32.sys
nvhda64.sys
nvhda32v.sys
nvhda64v.sys
PS C:>

I’ll then use that list and pass the unsigned drivers list to “Verifier.exe /standard /driver $UnSigned” to enable some Special driver Verification for finding the cause of some blue-screens.
I guess this script should work quite well also on Windows 7, but I’ve not tried it.

Hello world!

Welcome to my new Blog Site which will cover Geek Stuff in my life, mainly related to Windows and Microsoft infrastructure things that I find interesting in my work.

I’m working for TrueSec as an Executive Response Engineer, which is kind of the same role I had when I was working for Microsoft with Critical Problem Solving on site at customer.

Besides doing troubleshooting of critical (or not so urgent) problems, and normal consulting jobs, I’m also a MCT (Microsoft Certified Trainer) delivering trainings related to Windows and Security. Both Microsoft Official Courses and more in-depth Mastering classes at Labcenter in Sweden and Truesec Inc in the States.