Mastering SIEM Rules For Proactive Threat Detection

SIEM (Security Information and Event Management) systems are critical for identifying and responding to security threats in real time. Customizing SIEM rules helps reduce false positives and improves incident response efficiency. Below are key strategies and practical implementations to enhance your SIEM deployment.

You Should Know:

1. Writing Effective SIEM Rules

To minimize false positives, SIEM rules must be precise. Here’s an example of a Sigma rule for detecting suspicious PowerShell execution:

title: Suspicious PowerShell Execution 
description: Detects unusual PowerShell command-line arguments 
author: SOC Team 
logsource: 
product: windows 
service: powershell 
detection: 
selection: 
CommandLine|contains: 
- "-nop" 
- "-exec bypass" 
- "-EncodedCommand" 
condition: selection 
falsepositives: 
- Legitimate administrative scripts 
level: high

2. Reducing Noise with Correlation Rules

Combine multiple events to filter out benign activities. For example, a rule that triggers only after multiple failed logins followed by a successful one:

SELECT COUNT() as FailedLogins, UserName 
FROM WinEventLog 
WHERE EventID = 4625 
GROUP BY UserName 
HAVING COUNT() > 5 
FOLLOWED BY 
SELECT UserName 
FROM WinEventLog 
WHERE EventID = 4624

3. Leveraging Threat Intelligence Feeds

Enhance detection by integrating threat feeds (e.g., AlienVault OTX, MISP). Use Linux commands to automate feed ingestion:

 Fetch and parse threat intelligence 
curl -s https://otx.alienvault.com/api/v1/pulses/subscribed | jq '.results[].indicators[]' > threats.json

4. MITRE ATT&CK Mapping

Align rules with MITRE techniques (e.g., T1059 for PowerShell attacks). Use this Splunk query to map events:

index=windows EventCode=4688 Process="powershell.exe" 
| stats count by CommandLine 
| lookup mitre_techniques.csv technique OUTPUT technique_name

5. Automating Response with SOAR

Trigger automated actions (e.g., block IPs via firewall) using Python and APIs:

import requests 
headers = {"X-Auth-Token": "API_KEY"} 
response = requests.post("https://firewall/api/block", json={"ip": "1.2.3.4"}, headers=headers) 
print(response.text)

What Undercode Say:

SIEM tuning is an ongoing process—regularly review and update rules.
Use `logrotate` in Linux to manage SIEM logs efficiently:
```
logrotate -f /etc/logrotate.conf 
```

Windows administrators should audit logs via:

Get-WinEvent -FilterHashtable @{LogName='Security'; ID=4625}

For Splunk, optimize searches with tstats:

| tstats count WHERE index=wineventlog BY _time span=1h

Always test rules in a staging environment before deployment.

Expected Output:

Reduced false positives.
Faster threat detection and response.
Improved alignment with MITRE ATT&CK.

Relevant URLs:

References:

Reported By: Adeel Mustafa – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅

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