Category: Security

Replacing AppLocker with Microsoft Defender Application Control in Windows 10 1903 and later

Forget AppLocker and all its weaknesses and start using Microsoft Defender Application Control for superior application whitelisting in Windows 10 1903 and later.

This is a guide to get you started within an hour or two with what I call “AppLocker Deluxe” and that is Microsoft Defender Application Control, formerly known as Device Guard and up until recently Windows Defender Application Control (WDAC).

Most customers that did not use AppLocker before Wannacry and other types of ransomware attacks are now using AppLocker to prevent malicious software to run on their Windows devices. As many security specialists have shown, there are numerous ways to bypass AppLocker and still get code to execute. One of them being using regsvr32 to download and execute script directly from the internet for instance.

What is superior to AppLocker is Microsoft Defender Application Guard (MDAC). This takes application whitelisting to a new level and with Windows 10 version 1903 it becomes the first time since Windows 10 launched that it is actually usuable in many common day scenarios as the administration can now be on a level which is really to manage. The reason for this it being rather easy to manage now is primarily:

  • Multiple policies. You can have multiple policies complementing each other so that you do not have to sign everything nor have to create an entirely new baseline each time you want to allow new things to run.
  • Path rules. You can use path rules as of Windows 10 version 1903. As always, this is a balance between security and useability and administration so bear in mind and use this with caution. What is good is that MDAC comes with a use writable protection.

Pre-reqs for getting started

So to get started in something that looks like a real world scebario you need this:

  • 2 physical machines, different hardware models, that run Windows 10 version 1903 or preferably 1909 or later as that gives you some better insights.
  • A couple of hours of your time to get going!

High level steps

  1. Create a baseline on each hardware model.
  2. Merge the baselines into one general baseline.
  3. Create a supplemental policy.
  4. Deploy the two policies.
  5. Start the testing.
  6. Switch from Audit to Enforced mode!

1. Create a baseline on each hardware model

Let’s start with creating a baseline policy from two different machines, which will later be merged to one baseline policy. We will start with auditing, and eventually in the end of this guide switch to enforced mode.

$CIPolicyfileXML = "C:\temp\CIpolicy_model.xml"
New-CIPolicy -MultiplePolicy -filePath $CIPolicyfileXML -ScanPath C: -level FilePublisher -UserPEs -Fallback Hash

Now we set the necessary options for the code integrity policy, which is to use Microsofts Intelligent Security Graph for whitelisting (option 14), to allow supplemental policies to be used (option 17) and then we set Hardware Virtualized Code Integrity (HVCI) to Enabled.

#Automatically trust what Microsoft has deemed trustworthy using the Intelligent Security Graph
Set-RuleOption -FilePath $CIPolicyfileXML -Option 14
#Set the following option to make sure the policy can be applied without reboot
Set-RuleOption -FilePath $CIPolicyfileXML -Option 16
#Set this policy to allow supplemental policies, otherwise we can't supplement this basepolicy
Set-RuleOption -FilePath $CIPolicyfileXML -Option 17
#Now activating Hardware Virtualized Code Integrity (HVCI) and set it to enabled
Set-HVCIOptions -Enabled -FilePath $CIPolicyfileXML

Repeat the above process for at least two models, but preferably for each model you have in your environment (or at least the top five mot used models).

Note: Enabling the Intelligent Security Graph option will white list the installer for 7-Zip for instance. It will then also white list all executables that the 7-Zip installer puts on your system.

2. Merge the baselines into one general baseline

We will now merge the baselines from the two models (or more) and create one single baseline policy.

#When done collecting CIPolicies, merge them to create a common baseline
$CIPolicyfileXMLMerged = "C:\temp\Merged.xml"
$CIPolicyfileBin = "c:\temp\Merged.cip"
Merge-CIPolicy -OutputFilePath C:\temp\merged.xml -PolicyPaths "C:\temp\CIPolicy_modelX.xml","C:\temp\CIPolicy_modellY.xml"
#Then convert to binary format
ConvertFrom-CIPolicy -XmlfilePath $CIPolicyfileXMLMerged -BinaryFilePath $CIPolicyfileBin

Last but not least you must change the name of the Merged.cip file to match the Policy ID of the file which can be found at the bottom in the Merged.xml file, see the <PolicyID> section. The end result should look like {76300157-42A0-4A2D-A383-AF140D64AAE0}.cip.

3. Create a supplemental policy

Now we will create the first supplemental policy to supplement the baseline policy created in step 1 and 2. This is using path rules which is something that was added with Windows 10 version 1903.

#Now create a supplemental policy with file path rules
$CIPolicyfileXMLSupplemental = "C:\temp\Supplemental.xml"
$rules = New-CIPolicyRule -FilePathRule "C:\Program files\*"
$rules += New-CIPolicyRule -FilePathRule "C:\Program files (x86)\*"
$rules += New-CIPolicyRule -FilePathRule "\\server1\installation\*"
New-CIPolicy -FilePath $CIPolicyfileXMLSupplemental -Rules $rules -UserPEs
Set-CIPolicyIdInfo -FilePath $CIPolicyfileXMLSupplemental -BasePolicyToSupplementPath $CIPolicyfileXMLMerged
#now lookup the PolicyGUID from the bottom of the Supplemental.xml file.
ConvertFrom-CIPolicy -XmlFilePath $CIPolicyfileXMLSupplemental -Binary Supplemental.cip

You must change the name of the Supplemental.cip file to match the Policy ID of the supplemental file which can be found at the bottom in the Supplemental.xml file, see the <PolicyID> section. The end result should look like {56B75B7A-06D3-49EF-BCF8-8FC47C6ADA20}.cip.

4. Deploy the two policies

Now, lets deploy the two policies by copying them to C:\Windows\System32\CodeIntegrity\CIPolicies\Active.

For the sake of it, restart the machine. You could also use the below PowerShell command to refresh the policy without reboot:

Invoke-CimMethod -Namespace root\Microsoft\Windows\CI -ClassName PS_UpdateAndCompareCIPolicy -MethodName Update -Arguments @{FilePath = 'C:\Windows\System32\CodeIntegrity\CiPolicies\Active\{GUID}.cip'}

5. Start the testing

Now you can start the testing and see what is blocked by fetching the log files which are located in Event Viewer under Applications and Services Logs > Microsoft > Windows > Code Integrity > Operational.

6. Switch from audit mode to enforced mode!

Out of everything that would have been blocked by fetching the logs as mentioned in step 5, create additional supplemental policies and deploy until everything you need to run is white listed. Then, switch from audit mode to enforced!

Set-RuleOption -FilePath $CIPolicyfileXML -Delete -Option 3

Deploying via Intune

Even though there are existing configuration settings for enabling Microsoft Defender Application Control in an Intune endpoint restrictions policy, enabling it via those settings will mean very limited control and you cannot use supplemental policies. So, therefore you need to deploy these control policies in another way.

1. Create a source folder in C:\ named MDAC, in which you create a folder named Source, where you copy the .CIP files.

2. Create a textfile named SchTask.ps1 and add the following content.

New-Item -Path "c:\" -Name "CI" -ItemType "directory"
Copy-Item -Path ".\{76300157-42A0-4A2D-A383-AF140D64AAE0}.cip" -Destination "C:\CI" -Force
Copy-Item -Path ".\{56B75B7A-06D3-49EF-BCF8-8FC47C6ADA20}.cip" -Destination "C:\CI" -Force
Copy-Item -Path ".\MDAC.ps1" -Destination "C:\CI" -Force
$Time = New-ScheduledTaskTrigger -Once -At 12:00
$User = "SYSTEM"
$Action = New-ScheduledTaskAction -Execute "powershell.exe" -Argument "-ex bypass -file `"C:\CI\MDAC.ps1`""
Register-ScheduledTask -TaskName "CI" -Trigger $Time -User $User -Action $Action -Force
Start-ScheduledTask -TaskName "CI"
Return 0

3. Create a textfile named MDAC.ps1 and add the following content.

Copy-Item -Path "C:\CI\{56B75B7A-06D3-49EF-BCF8-8FC47C6ADA20}.cip" -Destination "C:\Windows\System32\CodeIntegrity\CiPolicies\Active" -Force
Copy-Item -Path "c:\CI\{76300157-42A0-4A2D-A383-AF140D64AAE0}.cip" -Destination "C:\Windows\System32\CodeIntegrity\CiPolicies\Active" -Force
Return 0

4. As we will deploy this using a Win32 app, download the Intune content prep tool and run the following command from the extracted IntuneWinAppUtil.exe.

IntuneWinAppUtil.exe -c C:\MDAC\Source -s SchTask.ps1 -o C:\MDAC

5. Create a new Win32 app in Intune and use the following parameters when adding it:

Program install and uninstall command:
powershell.exe -ExecutionPolicy Bypass .\SchTask.ps1
Running as System.

Detection rules:
Type: File
Path: C:\Windows\System32\CodeIntegrity\CiPolicies\Active
File or folder: {GUID}.cip
Detection method: file or folder exists

6. Assign the app and wait for the MDAC policy to apply. This can be verified by running msinfo32.exe and watching the status for Windows Defender Application Control.

Next steps: Looking at the CSP for Application Control for even smoother deploying via Intune.

The business values of upgrading to Windows 10 v1903 / 19H1

As with all new Windows 10 releases, there are a bunch of new features and bells and whistles. To the business and end-users this can mean great benefits. Here are the business values of upgrading to Windows 10 version 1903 (also referred to as 19H1), from a business, security and IT perspective.

Note: Windows 10 v1903 / 19H1 is not yet released, the features exist only in current Insider builds, which are possible to try out if you opt your organization into Windows Insider for Business.

The business case

By deploying the Windows 10 v1903/19H1 update your organization can:

  • Save many minutes for each user in your entire organization
    Potentially you can save a few minutes times the X number of users per month in your organization, when your Windows devices are updated with new Windows updates. This is possible as the user login is done automatically after restart (with the screen locked of course), meaning your end users do not have to stare at the login screen waiting to start LOB apps.
  • End-user improvements for finding relevant resources
    Chrome integration with Timeline feature is added and improvements to searching and finding stuff is improved. This means that users can find relevant resources they are working on or have worked on faster than before. 
  • Reduction in help desk calls
    With the new features added in Windows 10 v1903/19H1 you can see a reduction of ~5%* or more help desk incidents and support calls. This is thanks to automated troubleshooters, disk space reservation changes and fixes that previously caused help desk calls.

Let’s break this down and go into more details!

Increase in user productivity

There are several new features and design changes that will increase user productivity.

  • Automatic sign-on after restart and updating saves many minutes!
    This time-saving feature is to this date only available for cloud-only domain joined Windows 10 devices, not domain joined, nor Hybrid Azure AD joined (although GPO configuration tend to state otherwise). What it means is that the end-user will save many minutes after each update and restart!
    The requirements for this is (except for cloud domain joined Windows 10 device): BitLocker enabled which is not suspended during upgrade, which in itself requires a TPM 2.0 chip and Secure Boot to be enabled.
  • Chrome Timeline extension
    The Timeline was introduced in Windows 10 v1803 and is a great way for the user to have all history of documents you worked on, sites you browsed etc. within a few clicks! With the Chrome Timeline extension (named Web Activities), the end-user will also see browsing history from Chrome in their Timeline.
  • Enhanced search and indexing
    The search feature in Windows 10 v1903/19H1 is now listing top used apps and recent activities (i.e. opened documents) providing easier and quicker access to recently used files and apps. At the same time, for power users, there is now an option to index the entire C: drive and not only what is available in the user data folder. The settings for this are found in Settings > Search > Searching Windows.
  • Restart without updating or upgrading 
    This feature has come and gone over the Windows 10 lifetime, but now it works as expected. Whenever a quality update or a feature update is installed, the user can now choose to shut down or restart without having to be forced to install the update. This is a real time-saver and can save the user quite some time and hassle as a forced updating of the device now has become optional.
  • Windows Light Theme
    This is not really something you can consider time or cost-saving but has the potential to really impact the end user. For the first time since Windows 10 launched in 2015, there is a new theme that means a better user experience if you prefer light colors and not dark. Switch to the Windows Light Theme by going to Settings > Personalization > Colors and choose Light in the drop down.

Reduction in support costs

Microsoft are adding new feature and have made design changes that will reduce support for Windows 10 starting with Windows 10 v1903/19H1.

  • Automated troubleshooters
    Ever since Windows 7 there are built in troubleshooters which can be used to ease the troubleshooting of Windows problems. Starting with Windows 10 v1903/19H1, Windows has the possibility to detect problems and prompt to run troubleshooters to fix problems, instead of the user having to call help desk.
  • WWAN connections for built-in SIM improvements
    If you have devices with built-in SIMs, now this works much more stable than ever. First, there has been a problem with if the connection is lost, it was impossible to re-connect without disabling the device from Device Manager. Now, if the connection is lost you can simply re-connect as expected. Another important change is that now you can via the UI change the WWAN connection to not be metered network, meaning everything will from an end-user perspective work as usual (thus with the impact that it will generate more data).
  • Reserved disk space minimizing problems
    With Windows as a Service it is imperative that the Windows device has enough disk space. With Windows 10 v1903/19H1 Microsoft has made the decision to reverse 7GB to be able to update itself. I think everyone can agree that a Windows device with 0 bytes left on the disk will with 100% certainty result in a help desk incident. This decision by Microsoft will not only reduce general support calls due to “out of disk space” issues, but also raise the possibilities that updates go well, which also reduces work load for IT.

Security

As with all new Windows 10 release, Windows 10 v1903/19H1 is no different. Security is a baseline pillar of the modern desktop and modern workplace, and with modern threats you cannot overlook this. Here are a couple of 

  • Complete secure browser experience, with Chrome, Edge and IE11
    Windows Defender Application Guard (WDAG) has been available for a few versions now and really provides a super secure browsing environment. As many organizations use Chrome (and some Firefox), now you can “tie up the sack” so to say and make sure that Chrome and Firefox also adhere to WDAG, using the WDAG extension for Chrome and Firefox. This way, you can use IE11 for the old legacy web apps, while using Chrome or Firefox for other internal or external apps and then Edge for creating an extremely secure browsing experience on the web. Of course, you can use only Edge and IE11 together as well, but many users tend to want to use Chrome after all. The dependency for using WDAG with Chrome and Firefox is to use the Windows Defender Application Guard Companion app (this is not needed if only using Edge and IE11).
  • Protection history for Windows Defender Exploit Guard features etc.
    Having history of protections for antivirus is something everyone expects and have solutions for, but what I want to highlight is that now you can find Exploit Guard protections here as well, meaning you can follow-up on actions related to Controlled Folders and Attack Surface Reduction. Go to Windows Security > Virus & threat protection > Protection history to find the history.

For IT

  • Windows Sandbox
    The Windows Sandbox is a container solution where you quickly can get an isolated Windows 10 instance running, for testing stuff out. The use cases for this solution becomes a lot more when you consider there are config file possibilities!
  • A bunch of new MDM possibilities…
    Many new MDM policies are added, and to be more precise 70** MDM settings are new for Windows 10 v1903/19H1. A few of them are listed in Changes in MDM enrollment documentation. You can also see all possible settings by taking an MDM enrolled device, go to Settings > Accounts > Access work or school > <click your join and then click the Info button> > Export results, and look at the last section which lists all possible settings which can then be referenced and investigated for options.
  • …as well as new GPO settings
    In general we don’t see as many GPO settings added as MDM settings to each new Windows release, but some new GPO settings are for Storage Sense and Specifying deadlines for Windows Update restarts after quality or feature updates have been installed. 

Modern management and deployment

Note: The below is not related nor dependent on Windows 10 v1903/19H1 release and applies to previous Windows versions as well.

  • Some highlights of Intune improvements since last Windows release:
    • BitLocker encryption status and TPM version reports.
    • Win32 app deployment feature is now General Availability – plus troubleshooting possibilities are added.
    • Rename a device from the Intune console – pushed to the device.
    • Security baselines so that you can secure your Windows devices easily.
    • ADMX templates adding some additional hundreds of settings that you can configure on your Windows devices!

Summary

With the changed support statement detailed by Microsoft last summer, many organizations decided to skip the spring releases and only deploy the fall releases of Windows 10.

With the above I think you have a good understanding on how your organization can benefit of deploying Windows 10 v1903/19H1 in many ways, and you can make a qualified decision on whether or not you will deploy the spring/H1 release of Windows 10. 

—————————————

Foot note:

* Very rough estimation based on my soon four year-experience with Windows 10 in multiple organizations.
** Based on Insider build 18356 compared to Windows 10 v1809. This number can change.

“The page can’t be displayed” in web apps after installing June (or July) CU update for Windows 10

Some web apps might not work after installing the June (or July) 2016 Cumulative Update for Windows 10.

Problem

After installing June (KB3163018) or July (KB3172985) cumulative updates for Windows 10 a specific web app was broken, when browsing to it in Internet Explorer 11 or Edge lead to ”The page can’t be displayed”.

Investigation

Looking at the System log in Event Log showed Schannel errors:

A fatal alert was generated and sent to the remote endpoint. This may result in the termination of the connection. The TLS protocol defined fatal error code 40. The Windows SChannel error state is 808.

Doing a network trace showed that the web app server negotiated the TLSCipherSuite TLS_DHE_RSA_WITH_AES_128_CBC_SHA.

Cause

Windows as of update https://support.microsoft.com/en-us/kb/3061518 no longer support ciphers with 512-bits. Note that this KB was released in May 2016 but not anywhere stated to affect Windows 10. Nothing related to these changes points to Windows 10, but as we can conclude, these changes are introduced with June 2016 CU for Windows 10 (and thereby carried forward to July CU and any other CU to come).

Workaround

Use the workaround described in the registry section workaround in https://support.microsoft.com/en-us/kb/3061518 to go back to the 512-bits settings.

Solution

Make necessary server configuration changes to support the better ciphers.

Busting a myth: AppLocker do not magically allow standard users to install applications or updates

The one most common misconception around AppLocker is the fact that it could be used to allow standard users to install stuff that in any normal case would require administrator privileges. This is absolutely 100% incorrect.

What AppLocker does is set a number of rules on what can be run and executed on a machine. It is important to note that if you allow something to run or be executed via AppLocker rules the user will still need the appropriate privileges if the setup or application itself require administrative privileges at some point in time such as when doing automatic updating for instance.

Windows client security lockdown with nifty tool from Microsoft

It’s been around for some time and if you did not already know about it Microsoft provide the free tool called Security Compliance Manager. You can use it to very easily manage and export a set of pre-configured (or settings that you configure on your own) settings that improve security. You can then export these settings to for instance a group policy and import it into your domain.

There are templates with pre-configured security lockdowns for Windows XP, Windows Vista and of course also Windows 7. The tool works great for creating a security baseline for your client machines but the only downside is that you cannot import nor in a convenient way compare the settings in the templates with what you currently have.

Case of the mysterious issues with UAC in Windows 7 and Windows Server 2008 R2

At the TechNet/MSDN after work I attended last week I got an interesting question on why a user (domain admin) gets a UAC popup on trying to access folders via Explorer which he knows for sure he is supposed to be able to access looking at the ACLs of the folder. Instead, when clicking OK on the UAC popup the ACL is populated with his account.

UAC requesting permission to continue

My first thought to this behavior was Explorer.exe not being able to elevate and the “split personality” i.e. the two security tokens involved when UAC is in effect. Here comes a more detailed explanation that I think is of interest to more. Note that this problem also covers some other scenarios such as AppLocker rules not appearing to work as intended for administrators. Read on to learn what is causing this.

First when UAC is enabled you get two security tokens when you log in, easily explained as one which contains the administrator privilege information and one which does not. Most of the times you run everything using the standard security token. When you for instance want to install software or change some system settings, then the security token containing the administrator privileges information is used.

If you do not explicitly request an application to launch with higher privileges, or the applications itself request higher privileges, all processes and applications run in the user context with the standard security token. Virtually all applications including Windows applications and processes are possible to elevate by right clicking and choosing “Run as administrator”. This is not true for Explorer.EXE though as all your attempts to elevate it will not result in any actual elevation. There are a few caveats with this and let us continue with the example of access certain files and folders.

So let’s have a look at what the ACL of the folder D:\Share looks like:

ACL of users\stenis folder before UAC continue

We can clearly see that there are no user accounts in this list. Under normal circumstances any user which is a member of the domain admins group should be able to access that folder but instead is presented with the UAC dialogue:

UAC requesting permission to continue

What happens when the user “stenis” in this case clicks “Continue” to that UAC dialogue box questions is that the ACL is populated with the user account in questions:

ACL of users\stenis folder after UAC continue

This happens because the fact that Explorer.exe cannot be elevated the normal Windows Explorer does not see that the user account should be able to access that folder. It is easy to verify as you can actually run Explorer.EXE elevated by changing the registry setting “RunAs” to “_RunAs” in HKEY_CLASSES_ROOT\AppID\{CDCBCFCA-3CDC-436f-A4E2-0E02075250C2}. Thanks goes to Andre Ziegler for this finding.

So what does this tell us? It is a somewhat strange problem but still by design. The fact is that this “problem” is not applicable to the folder and file access as described in this blog but also for AppLocker rules for instance, as many domain administrators must choose “Run as administrator” to be able to run software which they think they should be able to run without this little procedure.

Case of the AppLocker default rules issue

If you have started using AppLocker with Windows 7 you know that the default rules for executable files make sure that administrators can run anything on the box, and that everything from the Windows folder and Program files folder are allowed to be executed. There exists a slight problem with this set of rules.

The default rules are intended for non-administrator users on the machine to be prevented from running any software which is not already installed or managed centrally, in the Program files folder. The default rules are also intended to allow anything from the Windows folder to be executed. Both these rules are sort of safe, as a standard user per default cannot put files in the program files folder to execute them, nor anywhere in the Windows folder.

But, there is this but. Inside the Windows folder there is a folder called “temp”, which believe it or not, standard users can write stuff to and consequently executing it thereby bypassing all the nice security benefits that AppLocker provide.

Well, the standard user just cannot copy an executable to the Temp folder using Windows Explorer, but using traditional copy commands using the command prompt this is fine, and then the executable can be executed.

The problem here might not be that the average user can bypass AppLocker this way, but when securing servers or clients, potential attackers can use this to bypass your security rules.

A simple solution if running with the default rules is to simply add the Windows\Temp folder to the exception list, effectively blocking code from being executed.

Standard users installing applications? Say welcome to the new reality

If you think that you have come a far way making sure all users are running as standard users you must stop and rethink. Well, having all users as standard users is very good from many perspectives but with coming challenges your efforts must not stop there. A growing problem is the fact that more and more applications install in the user space, i.e. in the \users\username\appdata directory instead of the traditional “Program files”.

Also Windows 7 contain Windows Installer 5.0 which sports a new feature which makes the software vendors easily make Windows Installer (MSI files) that install software in the user space instead of program files, and thereby not requiring the user to be administrator or even require a UAC prompt for credentials for an administrative account.

The standard users of course think this is great, meaning they after all can install and run for instance Google Chrome without needing to ask that restrictive IT department. From the IT departments view this fact that standard users can install and run applications is a concern.

The answer to take care of this problem is simply the new Windows feature AppLocker. To be honest it is somewhat like Software Restriction Policies (SRP) but whatever bad things you have heard about SRP you can forget about them. AppLocker contains new features that make the implementation and ongoing management very easy compared to Software Restriction Policies. More about AppLocker in the AppLocker walkthrough.

Hide files and folders which users don’t have permission to

The other day I implemented the Microsoft tool Access-based Enumeration tool for the first time with a customer. The tool installs on Windows Server 2003 and present you with a new tab when you choose Properties on shares on the server. When activated it will make sure that users on their client computers don’t see files and folders in Windows Explorer to which they do not have permission.

Download the Access-based Enumeration tool

Collection of best practices guides

Microsoft is providing best practice analyzers for most of their server products and I have gathered them on a list, for your convenience. These best practices analyzers are extremely good for troubleshooting and for making sure that the servers are performing at their best. Here is the link for the article:
http://www.theexperienceblog.com/technical-articles/collection-of-best-practices-guides/