Azure Policy Components

Key Components of Azure Policy

Azure Policy is made up of several core components that help you define, assign, and enforce security standards within your environment. As a threat hunter, it’s crucial to understand how these components interact and how they can be tailored to your security needs.

1. Policy Basics - Policy Definition

A Policy Definition is the core rule that specifies what is allowed or disallowed within your environment. This is where you define the conditions that a resource must meet to be considered compliant or non-compliant.

  • Example: You can create a policy definition that requires all virtual machines (VMs) to use managed disks. If a VM is created without a managed disk, the policy will flag it as non-compliant.

  • Structure of a Policy Definition:

  1. Display Name and Description:

    • These identify the policy and provide context.

    • Display Name: Max 128 characters.

    • Description: Max 512 characters.

  2. Policy Type:

    • There are three policy types:

      • Builtin: Provided by Microsoft.

      • Custom: Created by users.

      • Static: Regulatory Compliance policies based on Microsoft audits.

  3. Mode:

    • Resource Manager modes:

      • all: Evaluates all resource types.

      • indexed: Evaluates only resource types that support tags and locations.

    • Resource Provider modes:

      • Different modes manage specific resource types, such as Kubernetes clusters, Key Vaults, Virtual Network Managers, and others, with varying levels of compliance and enforcement capabilities.

      • Example: Microsoft.Kubernetes.Data for managing Kubernetes components.

  4. Versioning (Preview):

    • Policies can support versioning using a {Major}.{Minor}.{Patch} format, indicating the level of changes in the policy.

    • Different states, such as deprecated or preview, indicate the status of policy versions.

  5. Metadata:

    • An optional field that tracks information about the policy definition.

    • Common properties include version, category, preview, and deprecated.

  6. Policy Rule:

    • Core logic defined under if-then conditions.

    • Example: In the policy for "Allowed Locations," it checks if a resource’s location is within a list of allowed locations, and if not, applies a "deny" effect.

  7. Effect:

    • The action to take when a resource is non-compliant, such as deny, audit, or deployIfNotExists.

Example of a Policy Rule:

{
  "if": {
    "field": "Microsoft.Compute/virtualMachines/storageProfile.osDisk.managedDisk.id",
    "exists": "false"
  },
  "then": {
    "effect": "deny"
  }
}

2. Policy Assignment

Once a policy is defined, it needs to be assigned to a scope where it can enforce or audit resources. The scope can be a subscription, resource group, or management group.

  • Example: You can assign a policy that enforces encryption on all storage accounts within a specific subscription, ensuring that all storage resources are compliant with your security requirements.

  • Scope: The range at which the policy will apply. This can be:

    • Management Group: Applies the policy across multiple subscriptions.

    • Subscription: Applies the policy across all resource groups and resources in a specific subscription.

    • Resource Group: Applies the policy to all resources within a specific resource group.

  • Exclusions: You can exclude specific resources or resource groups from the policy assignment, allowing for flexibility in environments with different requirements.

3. Initiative Definition

An Initiative is a collection of related policies grouped together to achieve a broader compliance goal. By grouping policies into initiatives, you can manage and apply multiple policies more efficiently.

  • Example: You could create an initiative called "Security Best Practices", which includes policies for:

    • Enforcing encryption on all storage accounts.

    • Applying Network Security Groups (NSGs) to all VMs.

    • Auditing public-facing resources.

Initiatives simplify management by allowing you to assign a set of policies with one action, rather than managing individual policies separately.

4. Policy Effects

Every policy has an Effect that defines what happens when a resource does not comply with the policy. The effect is how the policy enforces or audits the rules.

Common Effects:

  • Deny: Prevents a resource from being created if it doesn’t comply with the policy.

    • Example: A policy can deny the creation of a virtual machine that lacks disk encryption.

  • Audit: Allows the resource to be created but logs the non-compliance, so you can review it later.

    • Example: A policy can audit all VMs that don’t have NSGs, logging these for further review by the threat hunting team.

  • Append: Adds specific properties to a resource to make it compliant.

    • Example: Appends a required tag (like “costCenter”) to a resource that is missing it.

  • Modify: Changes the resource configuration automatically to enforce compliance.

    • Example: Modifies a storage account’s configuration to enable encryption automatically if it wasn’t enabled during creation.

  • DeployIfNotExists: Deploys a resource or configuration if it doesn’t exist.

    • Example: If a VM is created without a monitoring agent, Azure Policy can automatically deploy the agent to ensure compliance.

Choosing the Right Effect: As a threat hunter, you might use Audit or Deny for different scenarios. For instance, you could start with an Audit effect to see which resources are non-compliant, then switch to Deny once you’ve ensured that the policy won’t block legitimate resource creation.

5. Parameters

Policies and initiatives can include parameters to make them more flexible and reusable. Parameters allow you to customize the policy when assigning it to different scopes.

  • Example: You could create a policy that requires VMs to be located in a specific region. By using parameters, you can assign this policy to different resource groups and specify different allowed regions for each one.

How These Components Work Together

Here’s how you can leverage these components as a threat hunter:

  1. Define a Policy: You start by defining a policy to address a specific security concern (e.g., ensuring all VMs have encryption enabled).

  2. Assign the Policy: You assign the policy to the appropriate scope (e.g., all VMs in a specific subscription).

  3. Monitor Compliance: As resources are created and updated, Azure Policy continuously monitors compliance. Any non-compliant resources are flagged for review or automatically remediated.

  4. Use Initiatives: For broader security objectives, you can create an initiative that combines multiple policies (e.g., encryption, MFA enforcement, NSG application) into a single package.

  5. Review Logs: You use the compliance logs generated by Azure Policy to identify misconfigurations or vulnerabilities that need further investigation.

Real-World Example: Ensuring Network Security Groups (NSGs) on All VMs

You are tasked with securing an Azure environment where multiple teams deploy virtual machines. A major risk is that some teams might create VMs without Network Security Groups (NSGs), leaving them vulnerable to unrestricted inbound and outbound traffic.

Step-by-Step Approach:

  1. Define the Policy: Create a policy that requires every VM to have an NSG applied. If a VM is created without an NSG, the policy will either deny its creation or log it as non-compliant.

  2. Assign the Policy: Apply this policy to all production resource groups.

  3. Monitor Compliance: If any team deploys a VM without an NSG, Azure Policy will detect it. You can choose to audit these violations initially, then shift to denying the creation of non-compliant VMs once you’ve evaluated the policy’s impact.

  4. Automate Remediation: Use the Modify effect to automatically attach a default NSG if a VM is created without one, ensuring that all VMs are protected without manual intervention.

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