Sunday, April 25, 2021

How to Restrict Azure Firewall Access from Contributor, Owner Role?

 7 min to read.

Abstract

When I look at Azure Built In Role Documentation I always feel this is really big list of built in roles and hardly any Organization will require to create new Azure custom role.

However when you work with Azure Customers, your faith and beliefs are bound to fail. And if your customer is Bank, your concepts of Security will fail.

So my customer started big on Azure Firewall. It was maintained by their network administrators team. One fine day network admin discovered that the Azure Firewall is visible to all users with Contributor and Owner access.

Obviously the demand came that Owner/ Contributor should have full access EXCEPT Azure Firewall.

Damn Zero Trust!

Anyways, How to hide/ restrict Azure Firewall access from Azure Owner and Contributors? Read on…



Have you heard of Azure custom roles?

The solution is simple. We need Custom Owner and Contributor role that will have default access levels except for Azure Firewall.

Azure Built in Roles list is here - https://docs.microsoft.com/en-us/azure/role-based-access-control/built-in-roles.

If the Azure Built In Roles don’t meet the specific needs of your organization, you can create your own custom roles.

So we will need to build custom Owner and Contributor role that do not have access to Azure Firewall.

Always get Built in Role Definition first!

For simplicity I am going to build custom Contributor Role only. Same can be replicated for Owner Role too.

First let us grab the built in role definition of Contributor Role using Azure PowerShell.

If you do not have Azure PowerShell get it installed or use it from Azure Shell. I want to edit the role definition on my local laptop so I am using Azure PowerShell from my local machine.

First login to correct Azure Subscription and Azure AD. I have seen major bomb blasts due to wrong selection of Subscription and Azure AD Tenant.

Connect-AzAccount -Subscription YourSubscriptionID  -Tenant YourAzureADTenantName-Like-Something.onmicrosoft.com

Get Contributor Role definition in JSON format with below command –

Get-AzRoleDefinition -Name "Contributor" | ConvertTo-Json | Out-File "YourPath\Contributor.Json"

 

Make sure that correct Path is selected as per your choice in above command. The Contributor role definition JSON will be created at specified location and it looks similar to below screenshot. Open JSON in Visual Studio Code. [click to get better view].



Modify the Contributor Role to Restrict Azure Firewall access!

I copy pasted above Contributor Role JSON to another document in VS Code changed the name of file..

The name of the role I changed to “Contoso-Contributor.json”.

Now take quick steps as mentioned below –

1.      Remove the Id filed completely. When you create role in Azure PowerShell; ID filed automatically gets created for you.

2.      As this is going to be customer Azure Role; change “IsCustom” property to True.

3.      Change the description that suits to your needs. I changed it to – Contoso Contributor Grants full access to manage all resources, but does not allow you to assign roles in Azure RBAC, manage assignments in Azure Blueprints, or share image galleries. However  users with this role can't access Azure Firewall.

4.      To remove the firewall access we need to add below line in NotActions segment of JSON as below – Microsoft.Network/azurefirewalls/*"

When we added * above, this means all types of actions are removed / restricted for Azure Firewall Resources. Make sure that you add “comma” on second last line.

5.      Make sure you add the desired subscription at the bottom in “AssignableScopes” property. Unless subscription Id added the role will not be created. The format of subscription has to be as follows -

Refer to screenshot below – [click to get better view].



Create the Role Definition in Azure Subscription

Now run below PowerShell command to get the role created. Make sure you use the Path of your choice where Contoso contributor json definition is present.

New-AzRoleDefinition -InputFile "YourPath\Contoso-Contributor-NoFirewallAccess.json"

 

The output of the command will be shown as below – [click to get better view]



Assign the role to user

I have created a user named as Contoso User in My Azure AD as shown below – [Click to get better view]



Then go to Azure Subscription -> Subscription -> Select Subscription [which is used in AssignableScope] -> Access Control -> Add -> Role Assignment. Selected Contoso User and assigned custom contributor role – [click to get better view]



Verify Azure Firewall Access

So, I selected two users – One with Contributor role and other with Contoso-Contributor Role. When click on Azure Firewall; I can clearly see that even If the Contoso User has all the access same as normal Contributor; the Azure Firewall Resource is not visible – [click to get better view].



Conclusion

Hope this article helped to Custom Contributor role to restrict / hide Azure Firewall.

Happy access control!!

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