Question - how to handle inactive managed identities deployed by ALZ-Bicep

[MarcoJanse]

Let us know the feedback or general question

I am looking for some guidance in the documentation to handle inactive identities created by ALZ-Bicep for remediating policies as they pop up in the Defender for Cloud recommendations as inactive identities.

When I deploy all the custom policy assignments from ALZ-Bicep, a lot of system managed identities are created to remediate these policies. However, Defender for Cloud reports a lot of these identities as medium severity: Permissions of inactive identities in your Azure subscription should be revoked.
Some are even marked as critical, due to it's assigned permissions.
This alert gets triggered according to this description in Defender for Cloud:

Microsoft Defender for Cloud discovered an identity that has not performed any action on any resource within your Azure subscription in the past 45 days. It is recommended to revoke permissions of inactive identities, in order to reduce the attack surface of your cloud environment.

Some of these identities are not used at the moment, as I don't have these type of resources deployed in my Landing Zone, but this could always change in the future.
Others I haven't needed to remediate anything the past 45 days, but might be needed again in the future.

For example: the system managed identity Deploy-VMSS-Monitoring is deployed by a policy definition and creates a system managed identity, but is never used.

I suppose removing these permissions would remediate the issue or I could make exemptions for all these identities, but I'm looking for some best practice guidance on this matter.

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[oZakari]

Hi @MarcoJanse,

The managed identities used by Deploy-VMSS-Monitoring and other monitoring assignments, along with Change Tracking and MDFC Defender SQL, are specifically utilized to configure the Azure Monitoring Agent (AMA).

Based on your response, it sounds like the primary recommendation you’re seeing is: Permissions of inactive identities in your Azure subscription should be revoked, with this secondary one: Azure Security Recommendation Details.

For the subscriptions where you're receiving these recommendations, I assume there are no virtual machines, virtual machine scale sets, or SQL virtual machines, which would align with what you're seeing. Alternatively, it could be that these resources are already configured for AMA and are simply in a standby state. Would you mind confirming if either of those scenarios align with your subscriptions?

[MarcoJanse]

Sorry for the delay.
Your assumption is partly correct. I have indeed no Virtual Machines scale sets in these subscriptions, so the Deploy-VMSS-Monitoring managed identity is currently not used. However, I also seem to be getting these alerts on managed identities that have been inactive for more than 45 days, as there was nothing to remediate for resources I do have.

I hope this helps.

[oZakari]

Hi @MarcoJanse, thank you for the clarification. Since the identities are necessary for the policies to configure the Azure Monitoring Agent at scale, they will need to remain in place unless you’d prefer to utilize a different approach for associating the applicable resources with the data collection rules by potentially running scripts on a schedule

Alternatively, you could add an exemption for the MDFC to account for these specific policy-related identities. While the MDFC recommendations are advisory, the identities have a valid use case—they are in place to support new resources as they come online.

Regarding the privileged identities recommendations you've received, we can explore options to address this by either creating custom roles tailored to the required permissions or identifying a built-in role with fewer privileges (if available) to better align with the principle of least privilege.

@arjenhuitema please provide any additional context if needed.