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Protecting your assets with Windows Server 2016 Device Guard Part1

Categories: AppLocker, Backup, Device Guard, Hyper-V, Security, Veeam
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With Windows Server 2016 we get device guard https://www.microsoft.com/en-us/cloud-platform/windows-server-security

Enhance the protection of your applications on-premises or running in the cloud. Help ensure only trusted software runs on the server with Device Guard.

This means that we can now create policies on what are allowed to run on our servers in a more secure way than we know from applocker on desktops

In this example we have a Windows Server 2016 with Veeam installed and we want to protect against rouge applications / ransomware (this is not a veeam problem but just used as a example)

First off we block SMB in the firewall so don’t have a risk from a compromised workstation.

To get started with device guard i highly suggest the blogs from Matt Graeber @mattifestation / http://www.exploit-monday.com

A big thank you to Matt for posting his amazing content online

Windows Device Guard Code Integrity Policy Reference

http://www.exploit-monday.com/2016/12/updating-device-guard-code-integrity.html

Device Guard Code Integrity Policy Auditing Methodology

I have been following his guidelines on merging different policy’s to allow Veeam to function under the lockdown of the host

This post will show the start and the end result of the policy and additional post will show anything in between , its not a five minute now everything is working plan , there are mutiple issues with application spawning scripts and dynamic unsigned applications , but for many workloads this is very fast to get start with and give a very high return on time used

Following the procedure for whitelisting , i found that all of Veeam’s own binarys was signed with a few different certificates to they was easy to add to the policy

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That left some files that looks to be from 3rd parties that wasn’t signed they have been added to the allow list on a file hash level , this means when there is new update our for veeam we need to add any updated files to the policy and reapply it

On the server running veeam we enabled device guard

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Select a policy file that will be generated from the xml file with rules , from a security point of view anyone locally on the box can change the policy file so ACL needs to apply if logged on the box , or move to default system32 and for added security the policy can be signed

So with our policy applied and server rebooted , we have a functioning veeam and windows install

Now imagine a few the steps you have to go though to loose your data

1 , Logon on the veeam server

2, Open outlook is installed of some odd reason / Open webmail (if the server have internet acess for some off reason)

3,

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Download the odd worded email , click on the hml link that downloads a zip file and have a java script inside

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Ignore the warning and click once more

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and a few seconds later we have encrypted all our files including the backup data (bypassing both local defender client and firewall scanning)

Again the numbers of crazy decisions you have to go though to get this far is crazy, and still we see it

So what happends on our device guard protected server

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We do the same as before

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But with a different result

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And we can see that device guard prevented the script from running and saving the day

Protecting your secrets, one more step to remember

Categories: Active Directory, AD, Backup, Disaster Recovery, Password, TSM
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If you are using hosted backup with TSM there is one more step to cover when people leave the org

The protection for many hosted backups are

Protection against “rouge” TSM Administrator

Client Side Encryption

Protection against “rouge” Backup Administrator

Node ID

Node Password (separation of duties one for password one for encryption)

And the last one is the issue here as its often not rotated, default TSM is 90 days but looking at different hosted TSM password is often set to no expire

This is not a TSM problem but a problem with password rotation

In the perfect world, the NodeID password and the encryption is not known by the same person, but then nodeid / password / secret is in registry so an AD admin can access this

Scenario

TSM BA Client installed on demodc01.stackdemo.dk

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Starting the TSM client , prompting for Node Password on first backup

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Ready for Action

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Starting the first backup , prompts for encryption key , and after a short while the backup is completed

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On a rouge server, outside of the environment we install the TSM BA Client and reuse the nodeID and password from the disgruntled backup admin

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Adding the nodeid and nodepassword

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And we restore a dummy file to see that’s its working, and is prompted for the encryption key

dsmc q b “{DEMODC01\SystemState\NULL\System State\SystemState}\ntds.dit” -sub=y

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If we can’t remember where ntds.dit is located we can search for it

rest “{DEMODC01\SystemState\NULL\System State\SystemState}\\DEMODC01\C$|\WINDOWS\ntds\*” C:\EVILDC\ -sub=y

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And we can restore the files

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And we now have something we can attack , if we boot up in a winPE enviroment we can follow the procedure for system state and have a working domain controller

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If the attacker had access to the domain controller aka disgruntled former employee the password and encryption is available on the source node in registry , since TSM used both the password and the encryption to access TSM server and backup/restore data it needs to be stored somewhere that the service can access

It’s very hard to protect anything from a domain admin even with the assume breach state of mind

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So, we can logon without getting prompted for credentials/encryption

So what can we do

First off , prevent people from being disgruntled

And since we can’t control human nature change the password on the nodes, either scheduled or when high privilege staff leaves or both, and again the default for a TSM node is that it will be changed

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Single Node example, log on the TSM , change password

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Something old Something New

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And Success , and password change can be scripted so cycling the password shouldn’t be a big issue

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And our EvilDC can’t access TSM anymore and everything is back to normal