Protecting Azure Backups with Resource Guard – Part 2

Welcome to part 2 of my series on Azure Backup and Resource Guard. In my first post, I gave some background on the value proposition Resource Guard provides. In this post I’ll be walking through how to configure it and demonstrating it in action. I’ll be using the lab pictured below which is based off the Azure Backup demo lab I have up on GitHub.

Lab used to demonstrate Resource Guard

For this demonstration, I used my Azure AD tenant as the primary tenant where the Recovery Service Vaults will be stored. I have a small environment in my at home lab that is configured with a Windows Active Directory forest that is synchronized to that tenant. The Azure AD tenant acted as the secondary tenant containing the Resource Guard. Homer Simpson will act as the owner of the Resource Guard (perhaps he is someone in Information Security) in the tenant and Maggie Simpson will own the subscription containing the workload and Recovery Services Vault (emulating a typical application owner) in the tenant.

Since both users are sourced from my on-premises Windows Active Directory forest and synchronized to, I used Azure AD’s B2B feature to invite Homer Simpson into the tenant. Once added through the B2B process, I setup an RBAC assignment granting Homer Simpson Owner of the subscription containing the Resource Guard.

Role Assignment in tenant

Next up I went to create the Resource Guard in the GIW tenant and received the error below when attempting to create the Resource Guard resource in the GIW Tenant.

Error creating Resource Guard

The error message was pretty useless (not atypical of Azure errors). In this case, this error is due to the Microsoft.DataProtection resource provider not being registered in this subscription. Once registering the resource provider in question, the Resource Guard was provisioned without issue. One thing to note is that while the Resource Guard can exist within a different resource group, subscription, or tenant, it must be in the same region as the Recovery Services Vault it is protecting.

Registering Microsoft.DataProtection resource provider

Once the Resource Guard resource was provisioned, I needed to give Maggie Simpson appropriate access over the Recovery Services Vault in the tenant. For that, I provisioned a role assignment for the Contributor role on the subscription to the System Operators group synchronized from on-premises that Maggie is a member of.

Role Assignment in tenant

Navigating to the Recovery Services Vault, Maggie Simpson is capable of modifying the soft delete feature (note it’s disabled for the purposes of this lab so the resources can be easily removed).

Prior to Resource Guard, Maggie Simpson can modify Soft Delete

Switching over to Homer Simpson and logging into the tenant, I attached the Resource Guard to the Recovery Services Vault. The interface allowed me to select the tenant (directory) and the Resource Guard resource.

Enabling Resource Guard

I had configured the Resource Guard to protect all the operations it was able to. This is confirmed with the confirmation in the screenshot below.

Resource Guard configured to protect sensitive operations

Once the Resource Guard is enabled, navigating back to the Security Settings of the Recovery Services Vault displays a message that Resource Guard is now enabled.

Switching back to Maggie Simpson, I then attempted to modify a backup policy which is considered a sensitive operation and is restricted via the association to the Resource Guard. As expected, Maggie Simpson cannot make the modifications to the Recovery Services Vault without authenticating to the GIW tenant and being authorized on the Resource Guard.

Maggie Simpson blocked from using Resource Guard

Success! Here we demonstrated how we can restrict sensitive operations on an Azure Backup Vault even when a user has a high level of permissions on the vault itself. Resource Guard provides a great security mechanism to establish the blast radius that works best for your organization. I could even add Azure AD PIM to the mix in the support just-in-time access of the Resource Guard. The support for cross-tenant specifically is very unique because there are very few (if any) other Azure resources that allow you to leverage a cross-tenant security boundary.

If you’re using Azure Backup, you should be using Resource Guard as an additional security control to add to the controls you are enforcing with Azure RBAC and Azure Policy. With the introduction into preview of the immutable vaults, Microsoft is providing a variety of tools to take a defense-in-depth approach using the technical features that make the most sense to the needs of your organization. WIth that bit of sales speak, I’m out for the weekend.

Thanks for reading!

Protecting Azure Backups with Resource Guard – Part 1

Hello geeks!

I recently was asked to talk about Azure Backup with a customer. Whenever I’m asked about a service my order of operations is to read through the public documentation, lab it out, talk to peers about it, and then put together key findings, best practices, and a deployable lab. I’ve published the package I put together for Azure Backup on GitHub.

When doing my research into Azure Backup, I came across an interesting limitation. The Recovery Services Vaults (RSVs), which orchestrate and manage storage of the Virtual Machine (VM) backup, must be created in the same subscription as the VMs being backed up. This surprised me, because it puts the resource being backed up and the backup itself within the same authorization boundary.

If you’ve done any work in AWS, you know best practice is to store the backups of the EC2 instances in a separate AWS account to ensure you aren’t stacking both the resources and backup in the same security boundary. The Code Spaces hack is a great example of what happens when you don’t do this. In the Azure scenario, I’m forced to take the risk of an attacker gaining Owner-level permissions of the subscription and locking/destroying both my resource and backup creating quite nasty ransomware scenario. What the heck Microsoft?

Thankfully, in 2021 Microsoft introduced a really creative feature to address this risk in the form of Resource Guard. A Resource Guard is an Azure resource that can be created in the same subscription, a different subscription in the same Azure AD tenant, or even a subscription in a different Azure AD tenant! When associated to an RSV, a user looking to make risky modifications to it (such as removing soft delete) must have permissions on BOTH the Resource Guard and the RSV. This means it can support separate authorization boundaries at the subscription level or even completely separate identity and authentication boundaries at the tenant.

Resource Guard isn’t something I often hear discussed by Microsoft folks when explaining Azure Backup to customers. Given what I’ve explained above, it should become quite obvious this is a critical feature to incorporate into your design if you plan on using Azure Backup.

In the next post in this short series, I’ll walk through a demonstration of the feature in action using the lab in this repository with the addition of a second Azure AD tenant as pictured in the image below. See you next post!

Azure Backup Lab for this series