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Update create-wdac-deny-policy.md

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windows/security/threat-protection/windows-defender-application-control/create-wdac-deny-policy.md
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@ -14,7 +14,7 @@ author: jgeurten
ms.reviewer: jsuther1974
ms.author: dansimp
manager: dansimp
ms.date: 12/03/2021
ms.date: 11/29/2021
ms.technology: windows-sec
---
@ -30,19 +30,19 @@ Topics this article will be discussing are:
5. Best Practices
6. Tutorial/Walkthrough
## File Rule Precedence Order
## File Rule Precendence Order
To create effective WDAC deny policies, it is crucial to understand how WDAC pares the policy. The WDAC engine evaluates files against the policy in the following order.
To create effective WDAC deny policies, it is crucial to understand how WDAC parses the policy. The WDAC engine evaluates files against the policy in the following order.
1. Explicit deny rules - if there is an explicit deny rule, do not process the rest of the rules; the file is untrusted.
2. Explicit allow rules.
3. WDAC will then check for the Managed Installer extended (EA) [Allow Apps with a WDAC managed Installer](configure-authorized-apps-deployed-with-a-managed-installer.md).
3. WDAC will then check for the [Managed Installer extended (EA)](configure-authorized-apps-deployed-with-a-managed-installer) or the [Intelligent Security Graph (ISG) EA](https://docs.microsoft.com/en-us/windows/security/threat-protection/windows-defender-application-control/use-windows-defender-application-control-with-intelligent-security-graph) on the file.
4. Lastly, WDAC will call the Intelligent Security Graph (ISG) to get reputation on file, if the policy has support for the ISG.
Explicit allow and deny rules encompass rules at any level (for example, hash rules, signer rules path rules, attribute rules, or package family name rules). If there is an explicit deny rule, WDAC does not process any other rules, meaning a deny rule always takes precedence in the case where a deny and allow rule would be at odds.
Explicit allow and deny rules encompass rules at any level (e.g. hash rules, signer rules path rules, attribute rules or package family name rules). If there is an explicit deny rule, WDAC does not process any other rules, meaning a deny rule always takes precedence in the case where a deny and allow rule would be at odds.
## Interaction with Existing Policies
### Adding Allow Rules
@ -90,7 +90,7 @@ If the policy enables user mode code integrity via the ***Enabled:UMCI*** rule-o
</SigningScenarios>
```
## Single Policy Considerations
If the set of deny rules is to be added into an existing policy with allow rules, then the above Allow All rules should not be added to the policy. Instead, the deny policy should be merged with the existing WDAC policy via the WDAC Wizard [Windows Defender Application Control Wizard Policy Merging Operation](wdac-wizard-merging-policies.md) or using the following PowerShell command:
If the set of deny rules is to be added into an existing policy with allow rules, then the above Allow All rules should not be added to the policy. Instead, the deny policy should be merged with the existing WDAC policy via the WDAC Wizard [Windows Defender Application Control Wizard Policy Merging Operation - Windows security | Microsoft Docs](https://docs.microsoft.com/en-us/windows/security/threat-protection/windows-defender-application-control/wdac-wizard-merging-policies) or using the following PowerShell command:
```PowerShell
$DenyPolicy = <path_to_deny_policy>
@ -99,20 +99,22 @@ Merge-CIPolicy -PolicyPaths $ DenyPolicy, $ExistingPolicy -OutputFilePath $Exist
```
## Multiple Policy Considerations
If you are currently using [multiple policies] (deploy-multiple-windows-defender-application-control-policies.md) on a device, there are two options for integrating the blocklist into your policy set.
If you are currently using [multiple policies](deploy-multiple-windows-defender-application-control-policies.md) on a device, there are two options for integrating the deny list into your policy set.
(Recommended) The first option is to keep the blocklist as its own policy isolated from your allow policies as it is easier to manage. Since applications need to be [allowed by both WDAC policies to run on the device](deploy-multiple-windows-defender-application-control-policies.md#base-and-supplemental-policy-interaction), you will need to add the Allow All rule(s) to your deny policy. This action will not override the set of applications allowed by WDAC illustrated by the following example:
(Recommended) The first option is to keep the deny list as its own policy isolated from your allow policies as it is easier to manage. Since applications need to be [allowed by both WDAC policies to run on the device](deploy-multiple-windows-defender-application-control-policies.md#base-and-supplemental-policy-interaction), you will need to add the Allow All rule(s) to your deny policy. This will not override the set of applications allowed by WDAC illustrated by the following example:
Policy 1 is an allowlist of Windows and Microsoft-signed applications. Policy 2 is our new deny policy that blocks MaliciousApp.exe with the Allow All rules. MaliciousApp.exe will be blocked since there is an explicit block rule in Policy 2. Windows and Microsoft applications will be allowed since there is an explicit allow rule in Policy 1 and Policy 2 (due to the Allow All rules). All other applications, if not Windows and Microsoft signed, for example, ExampleApp.exe, will not be allowed as this application is only trusted by Policy 2 (due to the Allow All rules) and not Policy 1.
Policy 1 is an allow list of Windows and Microsoft-signed applications. Policy 2 is our new deny policy which blocks MaliciousApp.exe with the Allow All rules. MaliciousApp.exe will be blocked since there is an explicit block rule in Policy 2. Windows and Microsoft applications will be allowed since there is an explicit allow rule in Policy 1 and Policy 2 (due to the Allow All rules). All other applications, if not Windows and Microsoft signed, e.g., ExampleApp.exe, will not be allowed as this application is only trusted by Policy 2 (due to the Allow All rules) and not Policy 1.
## Best Practices
1. **Starting with Audit Mode Policies** - as with all new policies, we recommend rolling out your new deny policy in Audit Mode and monitoring the [3077 block events](event-id-explanations.md#microsoft-windows-codeintegrity-operational-log-event-ids) to ensure only the applications you intended to block are being blocked. More information on monitoring block events via the Event Viewer logs and Advanced Hunting: [Windows Defender Application Control operational guide](windows-defender-application-control-operational-guide.md)
1. **Starting with Audit Mode Policies** - as with all new policies, we recommend rolling out your new deny policy in Audit Mode and monitoring the [3077 block events](event-id-explanations.md#microsoft-windows-codeintegrity-operational-log-event-ids) to ensure only the applications you intended to block are being blocked. More information on monitoring block events via the Event Viewer logs and Advanced Hunting: [Managing and troubleshooting Windows Defender Application Control policies](windows-defender-application-control-operational-guide.md)
2. **Recommeneded Deny Rules Types** - signer and file attribute rules are recommended from a security, manageability, and performance perspective. Hash rules should only be utilized where otherwise impossible. The hash of an application is updated for every new version released by the publisher which quickly becomes impractical to manage and protect against new threats where the attacker is quickly iterating on the payload. Additionally, WDAC has optimized parsing of hash rules, but devices may see performance impacts at runtime evaluation when policies have tens of thousands or more hash rules.
2. **Recommended Deny Rules Types** - signer and file attribute rules are recommended from a security, manageability, and performance perspective. Hash rules should only be utilized where otherwise impossible. The hash of an application is updated for every new version released by the publisher that quickly becomes impractical to manage and protect against new threats where the attacker is quickly iterating on the payload. Additionally, WDAC has optimized parsing of hash rules, but devices may see performance impacts at runtime evaluation when policies have tens of thousands or more hash rules.
## Creating a Deny Policy Tutorial
Deny rules and policies can be created using the PowerShell cmdlets or the WDAC Wizard [Microsoft WDAC Wizard (webapp-wdac-wizard.azurewebsites.net](https://webapp-wdac-wizard.azurewebsites.net) We recommend creating signer rules (PCACertificate, Publisher, and FilePublisher) wherever possible. In the cases of unsigned binaries, rules must be created on attributes of the file, such as the original filename, or the hash.
Deny rules and policies can be created using the PowerShell cmdlets or the WDAC Wizard [Microsoft WDAC Wizard](https://webapp-wdac-wizard.azurewebsites.net/) We recommend creating signer rules (PCACertificate, Publisher, and FilePublisher) wherever possible. In the cases of unsigned binaries, rules must be created on attributes of the file, such as the original filename, or the hash.
## Tutorial
@ -137,21 +139,20 @@ $DenyRules += New-CIPolicyRule -Level FileName -DriverFilePath <binary_to_block>
```
### Adding Allow All Rules
If necessary, as in the cases listed above, `[Allow All rules](48)` might need to be added to the policy. The Allow All rules can be manually added to the policy xml or by merging with the AllowAll xml present on the client system in the WDAC template folder:
If required, as in the cases listed above, [Allow All Rules](#adding-allow-rules) may need to be added to the policy. The Allow All rules can be manually added to the policy xml or by merging with the Allow All xml present on the client system in the WDAC template folder:
```PowerShell
$DenyPolicy = <path_to_deny_policy>
$AllowAllPolicy = $Env:windir + "\schemas\CodeIntegrity\ExamplePolicies\AllowAll.xml"
Merge-CIPolicy -PolicyPaths $DenyPolicy, $AllowAllPolicy -OutputFilePath $DenyPolicy
```
### Deploying the Deny Policy
Policies should be thoroughly evaluated and first rolled out in audit mode before strict enforcement. Policies can be deployed via multiple options:
1. Mobile Device Management (MDM): [Deploy WDAC policies using Mobile Device Management (MDM)](deploy-windows-defender-application-control-policies-using-intune.md)
1. Mobile Device Management (MDM): [Deploy WDAC policies using Mobile Device Management (MDM) (Windows)](deploy-windows-defender-application-control-policies-using-intune.md)
2. Microsoft Endpoint Configuration Manager (MEMCM): [Deploy WDAC policies by using Microsoft Endpoint Configuration Manager (MEMCM)](deployment/deploy-wdac-policies-with-memcm.md)
2. Microsoft Endpoint Configuration Manager (MEMCM): [Deploy Windows Defender Application Control (WDAC) policies by using Microsoft Endpoint Configuration Manager (MEMCM) (Windows)](deployment/deploy-wdac-policies-with-memcm.md)
3. Scripting: [Deploy WDAC policies using script](deployment/deploy-wdac-policies-with-script.md)
3. Scripting [Deploy Windows Defender Application Control (WDAC) policies using script (Windows)](deployment/deploy-wdac-policies-with-script.md)
4. Group Policy: [Deploy Windows Defender Application Control policies by using Group Policy](deploy-windows-defender-application-control-policies-using-group-policy.md)
4. Group Policy: [Deploy WDAC policies via Group Policy (Windows)](deploy-windows-defender-application-control-policies-using-group-policy.md)