master-client(-management)

Take Windows Up to 11

Tag: ConfigMgr

Install Microsofts January Meltdown / Spectre Updates during SCCM or MDT Build and Capture Task Sequence

Problem

I tried to create images of Windows 7 and Windows 10 (1607, 1703, 1709) with a SCCM Build and Capture Task Sequence. I deployed the January Windows Updates to the imaging clients so that the images should include the fixes for the Meltdown and Spectre vulnerabilities. But unfortunately this did not work. The reason is that the Antivirus compatibility Registrykey mentioned in this article had not been set before the updates were installed.

Update: After testing Build and Capture of Windows 10 with MDT I have added the necessary steps to the article.
Update 2: Thanks to @manelrodero for pointing out that a reboot is not required between setting the key and the Install Update step.
Update 3: Microsoft announced that this is not longer necessary beginning with the Cumulative Update 03-2018

Solution

You just have to add the registry in your Build and Capture sequence right before the update step performs the update scan.

SCCM

  1. Add a Run Command Line Step to your Build and Capture Task Sequence before the Install Updates step containing the following line
REG ADD "HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\QualityCompat" /v cadca5fe-87d3-4b96-b7fb-a231484277cc /T REG_DWORD /D "0x00000000" /F

QualityCompat Key
2. Make sure that the box Evaluate software updates from cached scan results is not checked in the first Install Updates step.

Install Updates step

MDT

  1. Add a Run Command Line Step to your Build and Capture Task Sequence before the Windows Update (Pre-Application Installation) step containing the following line
REG ADD "HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\QualityCompat" /v cadca5fe-87d3-4b96-b7fb-a231484277cc /T REG_DWORD /D "0x00000000" /F

QualityCompat Key

Use SCCM to bypass Device Guard / Applocker

Some days ago, my colleague Matthias (@mg_wtf) told me that he had just changed the executable of a package he had been testing in the ccmcache directory and had started the installation from the SCCM Software Center and it worked.

I checked several instances of SCCM Current Branch (up to 1710) and Technical Preview (up to 1711) and could verify the behavior in all of them. The agent validates the content only when downloading it. After that it assumes that it remains unchanged in the ccmcache directory. Edits of the files are very unlikely because only administrators are allowed to do that.

Update 2017/11/28 see section: Is this a big issue?

How I tested it

I installed and updated an instance of Windows 10 Enterprise 1703 and configured SCCM as a managed installer for Applocker and Device Guard as described here and here.

The Applocker policy allowed standard users only to execute applications from the Program Files or Windows folder and any APPX-Application. Everything else was blocked.

<AppLockerPolicy Version="1">
  <RuleCollection Type="Exe" EnforcementMode="Enabled">
    <FilePathRule Id="921cc481-6e17-4653-8f75-050b80acca20" Name="(Default Rule) All files located in the Program Files folder" Description="Allows members of the Everyone group to run applications that are located in the Program Files folder." UserOrGroupSid="S-1-1-0" Action="Allow">
      <Conditions>
        <FilePathCondition Path="%PROGRAMFILES%\*" />
      </Conditions>
    </FilePathRule>
    <FilePathRule Id="a61c8b2c-a319-4cd0-9690-d2177cad7b51" Name="(Default Rule) All files located in the Windows folder" Description="Allows members of the Everyone group to run applications that are located in the Windows folder." UserOrGroupSid="S-1-1-0" Action="Allow">
      <Conditions>
        <FilePathCondition Path="%WINDIR%\*" />
      </Conditions>
    </FilePathRule>
    <FilePathRule Id="fd686d83-a829-4351-8ff4-27c7de5755d2" Name="(Default Rule) All files" Description="Allows members of the local Administrators group to run all applications." UserOrGroupSid="S-1-5-32-544" Action="Allow">
      <Conditions>
        <FilePathCondition Path="*" />
      </Conditions>
    </FilePathRule>
    <FilePathRule Id="6c236a39-90f4-46bf-974a-b06995049062" Name="%WINDIR%\CCM\CcmExec.exe" Description="" UserOrGroupSid="S-1-1-0" Action="Allow">
      <Conditions>
        <FilePathCondition Path="%WINDIR%\CCM\CcmExec.exe" />
      </Conditions>
    </FilePathRule>
<RuleCollectionExtensions>
<ThresholdExtensions>
<Services EnforcementMode="Enabled" />
</ThresholdExtensions>
      <RedstoneExtensions>
        <SystemApps Allow="Enabled"/>
      </RedstoneExtensions>
</RuleCollectionExtensions>
  </RuleCollection>
  <RuleCollection Type="ManagedInstaller" EnforcementMode="Enabled">
    <FilePathRule Id="25656246-4c57-4f2f-bf72-baa5eb8c355b" Name="%WINDIR%\CCM\CcmExec.exe" Description="" UserOrGroupSid="S-1-1-0" Action="Allow">
      <Conditions>
        <FilePathCondition Path="%WINDIR%\CCM\CcmExec.exe" />
      </Conditions>
    </FilePathRule>
  </RuleCollection>
  <RuleCollection Type="Msi" EnforcementMode="NotConfigured" />
  <RuleCollection Type="Script" EnforcementMode="NotConfigured" />
  <RuleCollection Type="Dll" EnforcementMode="NotConfigured" />
  <RuleCollection Type="Appx" EnforcementMode="Enabled">
    <FilePublisherRule Id="a9e18c21-ff8f-43cf-b9fc-db40eed693ba" Name="(Default Rule) All signed packaged apps" Description="Allows members of the Everyone group to run packaged apps that are signed." UserOrGroupSid="S-1-1-0" Action="Allow">
      <Conditions>
        <FilePublisherCondition PublisherName="*" ProductName="*" BinaryName="*">
          <BinaryVersionRange LowSection="0.0.0.0" HighSection="*" />
        </FilePublisherCondition>
      </Conditions>
    </FilePublisherRule>
  </RuleCollection>
</AppLockerPolicy>

After that I executed the MyMalwareInstaller.exe as an administrator. This installation created a registry key and installed the c:\mymalware.exe.

Latter just shows a Messagebox with the executing user.

As defined in the Applocker policy the Administrator was allowed to start the MyMalware.exe

I switched to a standard user account without administrative rights and tried to execute the mymalware.exe. As expected this was blocked by AppLocker.

Hereafter I undid all the changes made by the installer and deployed a Test application via SCCM. This install did nothing else than creating the registry key specified as Application Detection Method.

Then I overwrote test1.exe in the Config Manager Client Cache directory (%windir%\ccmcache) with the MyMalwareInstaller.exe and deleted the detection key from the registry.

After executing the Application Deployment Evaluation Cycle the Software Center allowed me to install the application again. I clicked on the Install button and the SCCM client executed the mymalwareinstaller.exe instead of the checked in executable!

Then I switched back to the standard user and now he was able to execute the MyMalware.exe because it was installed by the SCCM client as Managed Installer.

You could argue both of these executables are not signed by a trusted publisher and SCCM even warns you about this when you import the application

However I tested this too and the client executes an unsigned executable instead of a signed one!

Is this a big issue?

Arguments in favor of No:

  • An attacker first needs to achieve administrative rights
  • The Applocker/Device Guard Managed Installer feature is still a beta feature
  • In this scenario it would be a lot easier for an attacker to copy his executable to the Program Files folder to let it run in the context of a standard user. But in tighter controlled environments this might be the loophole.
  • Update 2017/11/28: Dune Desormeaux from MS pointed out to me that they don’t claim that Device Guard protects against local admin rights.

Arguments in favor of Yes:

  • It is a possibility to execute code in the context of the SYSTEM account
  • Many Third-party Application Control systems leverage technologies similar to the Applocker/Device Guard Managed Installer
  • In an Advanced persistent threat scenario attackers could use this to gain persistent access to a system after an initial exploit even if application whitelisting is configured
  • If the attacker restores the content in the ccmcache and the detection rule after the successful execution of his code it is very hard to trace the way of the infection

Solution

In my opinion the best solution would be that the SCCM client checks the content hash before every execution from the cache instead of only directly after the download.

Before that happens, you should take this into account before using the SCCM client as a trusted source in an application control system.

Create LAPS managed user with SCCM Configuration Item

Microsoft has released LAPS (Local Administrator Password Solution) to easily allow different complex passwords for the local Administrator account on every client. It also allows to manage another user than the Built-in Administrator with the Well-Known SID (-500). But it does not create such a user.

In this article, I show you how to configure a SCCM Configuration Item to create such a user with a dynamic password.

Update: I removed an issue in the remediation script which did not always delete the password expiration time in a multi domain environment.

I won’t go into the details of configuring LAPS in your environment, there are already some really good articles about that topic.

The validation script

The validation script checks the following:

  • is LAPS enabled?
  • is LAPS installed?
  • is an Admin Account Name specified in the GPO?
  • Does the Admin Account exist?

The remediation script

The remediation script creates a local user with the name specified in the Group Policy and sets a random complex password. After that it deletes the expiration time attribute (ms-Mcs-AdmPwdExpirationTime) from the Active Directory computer object so that LAPS will set a new password on the next policy update. Finally, it triggers a policy update.

It does not add the user to the Administrator group. I recommend to do this with Group Policy.

Group Policy setting

If you want to manage another local user than the Built-in Administrator you have to configure the following policy setting in your Group Policies:

Computer Configuration\Policies\Administrative Templates\LAPS\Name of the administrator account to manage

Set it to enabled and enter the name of the local account you want to create.

LAPS GPO setting

Configuration Manager

Create Configuration Item

In the SCCM console go to Assets and Compliance - Compliance Settings - Configuration Items and click on the Create Configuration Item .

Specify a name and select Windows Desktops and Servers (custom) as type.

Select the Operating system versions you want to support (requires PowerShell).

Click on the New… button.

Specify a name for the setting and select as Setting type Script and as Data type String.

Click on the upper Edit Script… button in the Discovery script area. Then select PowerShell, and copy paste the following script to the script area.

Do the same with the lower Edit Script… button in the Remediation Script area with the following script.

Change to the Compliance Rules Tab and click on the New… button.

Define a Name for the rule select Rule type Value. The value returned by the specified script should be Equals the following values True.

Make sure you select the Run the specified remediation script when this setting is noncompliant checkbox.

You can choose the severity of this rule. For me Warning is high enough.

After that you can complete the creation of the Configuration Item.

Create Configuration Baseline

Now you have to create a Configuration Baseline in Assets and Compliance - Compliance Settings - Configuration Baselines .

Choose a Name for the baseline and Add the configuration item you have created earlier.

Deploy Configuration Baseline

After that you can Deploy the Configuration Baseline to a collection.

Please make sure to select the Remediate noncompliant rules when supported and the Allow remediation outside maintenance window check boxes.

Besides,you have to select how often this rule will be checked. I selected once per day.

Test the Configuration Baseline

After successfully deploying the baseline you should check the Configurations Tab in the Configuration Manager Properties Control Panel on one of your clients.

If the rule was not already evaluated press the Evaluate button.

After successfully evaluating the rule it will be shown as Compliant and the user was created.

The LAPS agent now has a target user and will soon change the password of the user and save this new password to the Active Directory object of the computer.

Hints

  • Check the DcmWmiProvider.log if you get any errors executing the baseline. There you can see the real PowerShell error.
  • If you see a message there like the one in the screenshot below you have to configure PowerShell execution policy to Bypass in the Computer Agent section in the Client settings or you have to sign the scripts with a Code-Signing-Certificate.


SCCM CB client push is not working on devices with TP agent

Problem

If you have installed the SCCM agent of a recent Technical Preview Build on a client it is not possible to push the current branch agent to it. I tested this with TP 1706 / CB 1702 and with TP 1707 / CB 1706.

This does not work even if the options Always install the client and Uninstall existing Configuration Manager client before the client is installed are selected.

As you can see in the log the request is skipped because a newer agent version is already installed.

Solution

You have to manually uninstall the Technical Preview agent before pushing from the CB console

%windir%\ccmsetup\ccmsetup.exe /uninstall

Task sequences are not showing up in SCCM Software Center when multiple users are logged on

Problem

I recently ran into the problem that the task sequence I wanted to test won’t show up in the SCCM Software Center. I checked for a common misconfiguration like

  • Deployment schedule
  • Configuration Manager Client active
  • Client in the correct collection
  • Deployment deployed to the correct collection
  • Client in a boundary with a distribution point
  • Packages deployed to the Distribution Point
  • Check the _SCCLient_%USER%.log, LocationServices.log, PolicyAgent.log, PolicyEvaluator.log,…
  • etc.

But all this was configured correct or did not show any errors.

Solution

I found out after some time that my colleague was still logged on to this computer. After logging him off the Deployments appeared as expected in the Software Center.

Knowing what to look for I found this thread:

Technet: Applications but not Programs showing in Software Centre

What have I learned:
Check if you have the lowest session ID when multiple sessions exist!