March 7, 2026

Summary

As part of a significant security transformation programme, an enterprise client operating in a heavily regulated industry needed to prepare for onboarding to a new Managed Detection and Response (MDR) service. With a complex global infrastructure, the organisation required a clear, evidence-based understanding of its security posture to ensure the successful integration and optimisation of its chosen Microsoft Sentinel SIEM/XDR platform.

Challenge

The primary challenge was a lack of visibility across the client’s diverse digital estate. Onboarding to an MDR service without a clear inventory of assets and telemetry would create significant alert noise, a high volume of false positives, and a poor return on investment. The client needed to avoid a costly and inefficient “boil the ocean” approach to data ingestion and instead focus security monitoring on the highest-value data sources from the outset.

Objectives

• Conduct a comprehensive security posture assessment to establish a baseline of the client’s environment.
• Map the corporate network to identify all endpoints, servers, and cloud resources.
• Prioritise high-value log sources essential for effective threat detection within Microsoft Sentinel.
• Tune and refine detection rules pre-emptively to minimise false positives upon service activation.
• Establish an efficient, repeatable process for onboarding new systems to the SIEM/XDR platform and MDR service.

Approach and Delivery

The engagement operated as a trusted adviser function from the initial assessment phase through to pre-onboarding readiness. The approach was grounded in a systematic discovery process, using a combination of automated tooling and custom PowerShell scripts to perform a thorough technical architecture assessment. This exercise built a detailed and accurate map of the client’s environment, which formed the foundation for all subsequent security integration decisions. The entire process was designed and documented to be repeatable, allowing the client to scale its security operations efficiently as the business evolved.

Technical Implementation

• Estate Discovery: PowerShell scripting was used extensively to automate the mapping of the client’s network. This provided a comprehensive inventory of endpoints, servers, and cloud resources that required monitoring.
• Log Source Optimisation: The discovery output was analysed to pinpoint the most valuable log sources for ingestion into Microsoft Sentinel. This included critical telemetry from Microsoft Defender for Endpoint, Defender for Cloud, and other key infrastructure components, ensuring that security data collection was both targeted and cost-effective.
• Proactive Detection Tuning: Before the MDR service went live, detection and analytics rules within Sentinel were tuned deliberately. Analysing the expected data flows from the prioritised log sources made it possible to pre-emptively adjust rule logic and reduce the false positives that often overwhelm new SIEM deployments.
• Configuration-as-Code Frameworks: To ensure consistency and future-proof the deployment, CIS-compliant security frameworks were developed for Microsoft Intune and Azure. These were delivered as configuration-as-code assets via PowerShell, enabling rapid, auditable, and repeatable deployments of security policies.
• Attack Surface Reduction (ASR): Drawing on CIS hardening principles, adaptable plug-and-play ASR rule policies were created in Intune. These policies could be tailored to different client environments to strengthen the baseline security posture with minimal administrative overhead.

Outcome

The client gained a clear, evidence-based understanding of their security posture and a prioritised list of data sources required for their new MDR service. This proactive discovery and tuning process significantly de-risked the onboarding project. By identifying critical telemetry and reducing alert noise in advance, the client was positioned to achieve a much faster time-to-value from their investment in Microsoft Sentinel. The delivery of a repeatable, code-based framework also empowered their internal teams to maintain and scale the solution effectively long-term.

Risks, Controls and Governance

Strong governance was embedded throughout the engagement. All deliverables were supported by detailed Statements of Work (SOWs) and high-quality change request documentation, providing a clear audit trail. The use of CIS-compliant frameworks and a configuration-as-code approach provided a robust, auditable foundation for the security enhancements. This structured methodology ensured that all changes were deliberate, documented, and aligned with industry best practices, mitigating the risk of misconfiguration and supporting regulatory compliance objectives.

Key Lessons

• Discovery Before Ingestion is Essential: Investing time in mapping an estate and identifying high-value log sources before connecting a SIEM/XDR is critical to avoiding an unmanageable flood of low-value alerts and associated costs.
• Proactive Tuning Reduces Operational Burden: Tuning detection rules before a security service goes live dramatically reduces the initial burden of false positives on a Security Operations Centre (SOC), allowing analysts to focus on genuine threats sooner.
• Automation Enables Scalability and Consistency: Using PowerShell for infrastructure-as-code and automated discovery creates a scalable and repeatable model for security onboarding, which is essential for maintaining a strong posture in large, dynamic enterprises.

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