Modernizing Your On-Prem SIEM with Microsoft Sentinel: Key Steps and Best Practices

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Introduction

Migrating from an on-premises SIEM (Security Information and Event Management) solution to Microsoft Sentinel is a strategic move for organizations seeking cloud-native security capabilities. This transition enhances scalability, reduces infrastructure overhead, and leverages AI-driven threat detection. However, the process requires careful planning, phased execution, and adherence to Microsoft’s best practices.

Learning Objectives

  • Understand the key phases of migrating from an on-prem SIEM to Microsoft Sentinel.
  • Learn essential PowerShell and KQL commands for data ingestion and rule migration.
  • Implement security hardening and log retention strategies in Sentinel.

You Should Know

1. Pre-Migration Assessment with PowerShell

Command:

Get-WinEvent -ListLog  | Where-Object {$_.RecordCount -gt 0} | Select-Object LogName, RecordCount

What it does:

This PowerShell command lists all active Windows Event Logs with recorded events, helping identify critical logs for migration.

Step-by-Step Guide:

1. Run the command in PowerShell (Admin mode).

2. Export the results to CSV for analysis:

Get-WinEvent -ListLog  | Where-Object {$_.RecordCount -gt 0} | Export-Csv -Path "EventLogs.csv"

3. Prioritize logs with high `RecordCount` for Sentinel ingestion.

2. Configuring Data Connectors in Sentinel

KQL Query for Validation:

SecurityEvent 
| where TimeGenerated > ago(1h) 
| summarize count() by EventID

What it does:

This Kusto Query Language (KQL) query checks if Windows Security Events are successfully ingested into Sentinel.

Step-by-Step Guide:

  1. Navigate to Sentinel > Data Connectors and enable the “Windows Security Events” connector.
  2. Deploy the Azure Monitor Agent (AMA) to on-prem servers.
  3. Use the KQL query above in Sentinel’s Logs blade to verify data flow.

3. Migrating Detection Rules with KQL

Example: Migrate a SIEM Rule to Sentinel

Original SIEM Rule (Splunk SPL):

index=windows EventID=4625 | stats count by src_ip

Equivalent Sentinel KQL:

SecurityEvent 
| where EventID == 4625 
| summarize count() by SourceIp

Step-by-Step Guide:

1. Export existing SIEM rules to CSV.

  1. Rewrite each rule in KQL using Sentinel’s Analytics blade.

3. Test rules with historical data before enabling.

4. Hardening Sentinel with Azure Policies

Azure CLI Command:

az policy assignment create --name 'sentinel-retention' --policy ' /subscriptions/{sub-id}/providers/Microsoft.Authorization/policyDefinitions/xxxxx' --params '{"retentionDays": {"value": 90}}'

What it does:

Enforces a 90-day log retention policy for Sentinel workspaces.

Step-by-Step Guide:

  1. Locate Azure Policy definitions for Sentinel (e.g., Deploy Diagnostic Settings for Microsoft Sentinel).

2. Assign policies via CLI or Azure Portal.

3. Audit compliance with:

az policy state list --resource-group "YourRG"

5. API Security for Sentinel Integrations

Restrict API Access with IP Whitelisting:

az storage account update --name "YourStorage" --resource-group "YourRG" --add properties.networkAcls.ipRules "123.45.67.89"

What it does:

Limits API access to Sentinel-linked storage accounts to trusted IPs.

Step-by-Step Guide:

  1. Identify APIs used for Sentinel integrations (e.g., Azure Log Analytics API).
  2. Apply IP restrictions via Azure CLI or Networking blade.

3. Monitor API calls with:

AzureDiagnostics 
| where ResourceProvider == "MICROSOFT.STORAGE" 
| summarize count() by CallerIPAddress

What Undercode Say

  • Key Takeaway 1: A 3–4 month migration timeline is realistic but varies by environment complexity. Prioritize log sources and rulesets to avoid bottlenecks.
  • Key Takeaway 2: Sentinel’s AI-driven analytics (e.g., UEBA) offer advantages over traditional SIEMs, but require proper data normalization.

Analysis:

Microsoft Sentinel’s cloud-native architecture reduces operational overhead but introduces new considerations like API security and cost management. Organizations should:
1. Start with a pilot (e.g., ingesting 10% of logs).

2. Use Azure Policy to enforce governance.

  1. Train teams in KQL to maximize Sentinel’s capabilities.

For further reading, refer to Jussi Metso’s blog: https://lnkd.in/d2b7CJyS.

IT/Security Reporter URL:

Reported By: Metso Modernizing – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅

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