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Introduction
In today’s sprawling hybrid enterprises, a single employee often juggles multiple accounts—a standard user account, a privileged admin account, and various service accounts. This identity fragmentation creates a massive security blind spot, allowing attackers to hop between accounts undetected. Microsoft Defender for Identity’s new preview feature, Custom Account Correlation Rules, tackles this head-on by letting you manually link disparate accounts, thus providing a single, unified view of a user’s identity and dramatically sharpening your threat detection.
Learning Objectives
- Master Identity Correlation: Learn to manually link fragmented identities in Microsoft Defender for Identity to eliminate security blind spots.
- Automate at Scale: Discover how to use PowerShell and the Microsoft Graph API to manage correlation rules programmatically.
- Operationalize Risk: Understand how correlated identities feed into Entra ID Protection to enforce risk-based conditional access (RBCA) policies.
You Should Know
- The Identity Fragmentation Problem: Why It’s a Goldmine for Attackers
Identity data sprawl is a fundamental security weakness. Sophisticated attackers exploit this fragmentation, moving laterally from a compromised low-privilege account to a privileged one, with security tools seeing each hop as an isolated, unrelated event. Without correlation, a suspicious login from a standard account and a privilege escalation from an admin account appear as separate incidents, allowing the attack to proceed unchecked. Microsoft Defender for Identity’s custom correlation rules solve this by stitching these accounts together. To get started, manually link accounts using the following steps:
- Navigate to the Microsoft Defender Portal and select “Identities.”
- Click on “Identity settings” and choose “Linked accounts.”
3. Click “Add linked accounts.”
- Select the primary identity (e.g., the user’s main corporate account).
- Add secondary accounts (e.g., admin, service, or cross-domain accounts).
- Apply tags to classify account types (e.g., Admin, Legacy, Service).
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Automating Identity Correlation with PowerShell and Graph API
Managing account links manually is not scalable for large enterprises. You can automate this process using the Microsoft Graph API and PowerShell, which allows you to correlate identities based on naming patterns or other attributes. This is critical for syncing links across your hybrid environment. Below is a script template to get you started:
Connect to Microsoft Graph with required scopes Connect-MgGraph -Scopes "User.Read.All", "SecurityActions.ReadWrite.All" Define the primary and secondary accounts using their IDs $primaryUserId = "[email protected]" $secondaryUserId = "[email protected]" Get the user objects $primaryUser = Get-MgUser -UserId $primaryUserId $secondaryUser = Get-MgUser -UserId $secondaryUserId Create the account correlation payload $correlationPayload = @{ "primaryAccountId" = $primaryUser.Id "linkedAccountIds" = @($secondaryUser.Id) } Invoke the Defender for Identity API to link the accounts Note: This is a conceptual endpoint. Check the latest Graph API docs for the exact URI. Invoke-MgGraphRequest -Method POST -Uri "https://graph.microsoft.com/beta/security/identities/correlationRules" -Body $correlationPayload
This script uses the Microsoft Graph PowerShell SDK, the modern replacement for legacy Azure AD modules, to programmatically enforce your identity correlation strategy.
3. Operationalizing Risk: From Correlation to Conditional Access
The true power of identity correlation is realized when it is fed into Entra ID Protection’s risk-based conditional access (RBCA) policies. As highlighted in the LinkedIn post, linking accounts allows Entra ID to unify risk signals, meaning a risky sign-in on a secondary account can elevate the risk level for the primary identity, triggering automated remediation like MFA challenges or password resets.
To configure this:
- Go to the Microsoft Entra admin center > Protection > Identity Protection.
2. Select User risk policy.
- Under “Assignments,” select “All users” (or specific groups) and set the User risk condition to “High” to start.
- Under “Access controls,” select “Allow access” and check “Require password change” or “Require MFA.”
5. Set “Enforce policy” to “On.”
When a linked admin account exhibits anomalous behavior, Entra ID Protection now understands the full identity context and can enforce a stronger policy for the principal user, blocking lateral movement in its tracks.
- Proactive Defense: KQL Hunting and Lateral Movement Paths
Once your identities are correlated, you need to hunt for threats that slipped through. Use Kusto Query Language (KQL) in Microsoft 365 Defender’s advanced hunting to query raw 30-day activity across all linked identities. This query, for example, finds any sign-in activity from linked accounts originating from non-corporate IP ranges:
let primaryAccountId = "[email protected]"; let linkedAccounts = (IdentityInfo | where AccountUpn == primaryAccountId | project LinkedAccountIds); AADSignInEventsBeta | where AccountUpn in (linkedAccounts) | where IPAddress !in (CorporateIPRange) | project Timestamp, AccountUpn, IPAddress, RiskLevelDuringSignIn
Furthermore, use Microsoft Defender for Identity’s Lateral Movement Paths (LMPs) to visualize how an attacker could hop from a standard linked account to a domain controller. This proactive view, powered by your new correlation logic, helps you identify and break the most dangerous attack chains before they are exploited.
What Undercode Say
- Correlation is the New Perimeter: In a perimeter-less world, stitching fragmented identities is the cornerstone of a robust Zero Trust architecture. Without it, you’re fighting a ghost.
- Automate to Dominate: Manual linking is for validation. Real security comes from automating correlation and subsequent risk mitigation via Graph API and conditional access policies.
- The Attack Surface Has Shrunk: By correlating privileged and standard accounts, you’ve effectively dismantled the attacker’s ability to move laterally without triggering a unified risk alert.
Prediction
Within the next year, identity correlation will become a mandatory compliance checkbox for SOC 2 and ISO 27001 in hybrid environments. We will see the rapid emergence of AI-driven identity correlation that automatically discovers and links accounts based on behavioral biometrics and usage patterns, not just static rules. Attackers who rely on fragmented identity silos will find their primary evasion strategy completely obsolete, shifting the cat-and-mouse game to more sophisticated, insider-threat based scenarios. Microsoft’s move here signals a broader industry pivot; expect competitors like CrowdStrike and SentinelOne to quickly follow with similar native identity correlation capabilities.
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