By Mike – Security Day Blog – This post will explain the importance of developing Sentinel rules for modern security systems.
👋 Introduction: Sentinel Rule Building Can Be Tough—Here’s How I Make It Easier
Let’s be real—building custom detection rules isn’t always easy.
There are days when everything clicks and the logic comes together fast. But other times, it can feel like you’re staring at raw logs for hours, unsure where to start or what to look for.
Over the past decade, I’ve built detection rules across dozens of environments—some simple, others highly complex. No matter the setup, one thing has always helped me get unstuck: working from examples.
Examples show me the logic I need. They inspire new ideas. And they help me stay focused when I’m not sure how to start.
So in this post, I’m sharing some of the ways I make rule writing easier—especially when working in Microsoft Sentinel. Whether you’re new to writing KQL or just want to improve your current process, this guide will help you build better rules with less stress.
🔎 What Are Context Packages in Sentinel?
Microsoft Sentinel offers helpful tools called Context Packages. These are found in the Content Hub and are built to help you get started fast with Sentinel rules and data ingestion.
Each package includes:
- Data connectors to collect logs
- Dashboards (Workbooks) to view activity
- Queries to help hunt for threats
- Detection rules to catch common attacks
- Templates and Watchlists for quick use
They save time and reduce guesswork. These packs are especially useful for tools like Azure AD, Microsoft 365 Defender, AWS, and Cisco ASA.
👉 Explore Sentinel Content Packs
🧩 What If You Use Unique or Older Tools?
Not every environment uses the latest tools. Some teams still rely on legacy systems or niche platforms.
Let’s say you use Epic for patient data or Citrix with an older firewall. These tools will not be covered by default Sentinel content.
But that’s okay—because Sentinel lets you bring in logs from almost anything. You can normalize that data, then write custom rules to detect the exact behaviors you care about.
This approach gives you control and flexibility, no matter what your tech stack looks like.
🧠 Creating a Sentinel Custom Rule
Here’s a simple example of a custom rule. It finds users who trigger a phishing alert and then log in using SSH. That kind of pattern could signal a compromised account.
let phishingAlerts = SecurityAlert
| where ProviderName == "Zscaler"
| where AlertName contains "Phishing";
let sshLogins = Syslog
| where ProcessName contains "sshd"
| where SyslogMessage contains "Accepted password";
phishingAlerts
| join kind=inner (sshLogins) on $left.Account == $right.Account
| where TimeGenerated between (phishingAlerts.TimeGenerated .. phishingAlerts.TimeGenerated + 10m)
This rule brings together data from two different sources. It helps your team see the full story—not just isolated events.
If you’re new to KQL, I recommend starting with Microsoft’s KQL Cheat Sheet. It’s a great resource for learning fast.
✅ Quick Checklist for Sentinel Rule Building
I’ve learned something simple but powerful: using examples makes rule building easier.
Examples teach you the logic. They spark ideas. And they push you in the right direction when you’re stuck. Don’t be afraid to ask AI tools like Copilot or ChatGPT to help shape a query or review your logic.
Here’s a checklist I recommend when building your own rule:
- ✅ Decide what behavior you want to detect
- ✅ Find the log sources that contain that behavior
- ✅ Use an example or template to get started
- ✅ Write clean KQL and include helpful comments
- ✅ Map key items like usernames, hosts, and IPs
- ✅ Test your rule using recent logs
- ✅ Add filters or limits to avoid false positives
- ✅ Link the rule to a playbook for automated response
Review your rules every few months. Remove any that are outdated and fine-tune the ones that still matter. Keep things fresh and useful.
📚 Real Sentinel Rule Ideas to Try
Here are some practical use cases you can try today:
| Use Case | What It Finds | Log Sources |
|---|---|---|
| Outdated Browser Used | Admins using unsafe browsers | Zscaler, Entra ID |
| SSH + File Write | Login followed by file access | Syslog, Linux Audit Logs |
| Off-Hours Login | Sign-ins late at night or on weekends | Azure Sign-In Logs, Events |
| Disabled Account Used | Logins from inactive accounts | Entra ID, Defender for Identity |
| Location Anomaly | Logins from far-apart places in short time | Azure AD, M365 Logs |
These rules help detect risky behavior early—before it turns into a real incident.
🚀 Use Sentinel Rules with Defender XDR
Sentinel is powerful on its own. But when you combine it with Microsoft Defender tools, you get even more value.
Here’s why it matters:
- Defender alerts flow directly into Sentinel
- Sentinel links those alerts into a single investigation
- You get richer context and fewer false alarms
- Your SOC team responds faster and with more clarity
The Microsoft XDR platform—Defender for Endpoint, Identity, Office 365, and Cloud Apps—works best when integrated with your Sentinel detections.
👉 Get Started Today
Explore the Sentinel Content Gallery to try prebuilt rules.
Practice writing queries with the KQL Cheat Sheet to build your confidence.
🗓️ Next week, I’ll show you how Sentinel and Security Copilot can work together so you can respond to threats faster and with less manual effort.
Please check out other posts at : Blog Posts – Its Security Day with Mike