Managing False Positives
Reduce alert fatigue by identifying and suppressing false positive security alerts while maintaining comprehensive threat coverage.
Some false positives are unavoidable in comprehensive security monitoring. The goal is to reduce noise without creating blind spots.
Understanding False Positives
| Impact | Description |
|---|---|
| Alert Fatigue | Too many false positives cause teams to ignore alerts |
| Wasted Resources | Analysts spend time on non-threats |
| Tuning Required | Detection rules need refinement for your environment |
Common False Positive Scenarios
- 🔧 Admin Tools
- 👤 Service Accounts
- 💻 Development
- 🔐 Authentication
Legitimate Administrative Tools
Scenario: IT team's PowerShell scripts trigger "Suspicious PowerShell Activity" alerts.
| Legitimate Activity | Why It Triggers Alerts |
|---|---|
| PowerShell remoting | Matches lateral movement patterns |
| Config management (Ansible, Puppet) | Executes on multiple systems |
| Automated patch scripts | System-level changes |
| Software deployment | Process execution patterns |
Service Accounts and Automation
Scenario: Service accounts with high privileges generate "Privilege Escalation" alerts.
| Activity | Why It Triggers |
|---|---|
| Backup agents | Access multiple systems |
| Monitoring agents | Elevated permissions |
| CI/CD pipelines | Deployment to production |
| Database replication | Cross-server access |
Development and Testing Activities
Scenario: Security testing tools trigger malware or attack alerts.
| Activity | Why It Triggers |
|---|---|
| Penetration testing tools | Attack-like behavior |
| Code obfuscators | Malware-like patterns |
| Security research VMs | Running malware samples |
| Load testing tools | Simulated attacks |
Authentication Patterns
Scenario: Normal authentication behaviors trigger "Brute Force" alerts.
| Activity | Why It Triggers |
|---|---|
| Multiple saved credentials | Wrong account attempts |
| Mobile app reconnections | Retry patterns |
| Password managers | Credential testing |
| VPN reconnections | Multiple auth attempts |
Reducing False Positives
- 1️⃣ Identify Pattern
- 2️⃣ Verify
- 3️⃣ Create Rule
- 4️⃣ Document
- 5️⃣ Review
Step 1: Identify the Pattern
Review recurring false positive alerts for common characteristics.
| Pattern Type | Questions to Ask |
|---|---|
| Source Host | Same server consistently triggering? |
| User Account | Specific service account involved? |
| Process Name | Legitimate application causing alerts? |
| Time Pattern | During scheduled maintenance? |
| Frequency | Multiple similar alerts quickly? |
Step 2: Verify Legitimacy
Always verify the activity is truly benign before suppressing alerts.
Verification checklist:
| Check | Action |
|---|---|
| Asset Owner | Confirm activity is authorized |
| Context | What happened before/after? |
| Business Process | Matches documented procedures? |
| Identity | Verify user/account authorization |
| Cross-Reference | Check other security tools |
Step 3: Create Suppression Rule
Navigate to Configuration → Detection Rules and create an exception.
Suppression options (use narrowest scope):
| Option | Example | Scope |
|---|---|---|
| Host-Based | Host: backup-server-01 | Narrow |
| Process-Based | Process: BackupAgent.exe | Medium |
| User-Based | User: DOMAIN\svc-backup | Medium |
| Time-Based | Daily 02:00-04:00 UTC | Temporary |
Step 4: Document the Exception
Add clear justification to the suppression rule.
| Field | Description |
|---|---|
| Business Justification | Why is this activity legitimate? |
| Approval | Who authorized the exception? |
| Review Date | When should this be re-evaluated? |
| Risk Assessment | What risk remains? |
Step 5: Monitor and Review
Regularly review suppression rules to ensure validity.
| Exception Type | Review Frequency |
|---|---|
| High-Risk | Monthly |
| Service Account | Quarterly |
| Development | Semi-annually |
| All Other | Annually |
Alternative Approaches
- 📊 Thresholds
- 🏗️ Segmentation
- 🔗 Correlation
Adjust Detection Thresholds
Modify rule sensitivity instead of completely suppressing.
Example: Authentication failure threshold
| Setting | False Positives | Missed Attacks |
|---|---|---|
| Alert on 3 failures | Many | Few |
| Alert on 10 failures in 5 min | Optimized | Optimized |
| Alert on 50 failures | Few | Many |
Environment Segmentation
Apply different detection rules to different environments.
| Environment | Detection Strategy |
|---|---|
| Production | Strict rules, immediate alerts |
| Staging | Standard rules, delayed notifications |
| Development | Relaxed rules, daily digests |
| Security Research | Minimal detection, logging only |
Correlation-Based Filtering
Use CastellanAI's correlation engine to filter isolated events.
Correlation reduces false positives by requiring:
| Requirement | Description |
|---|---|
| Multiple Events | Related events within time window |
| Multiple Categories | Events from different detection types |
| Baseline Deviation | Unusual pattern vs. normal behavior |
Best Practices
| Practice | Description |
|---|---|
| Use Narrowest Scope | Suppress specific combinations, not broad categories |
| Set Expiration Dates | Force periodic review of exceptions |
| Monitor Impact | Track how many alerts each rule blocks |
| Prefer Tuning | Adjust sensitivity instead of suppressing when possible |
📝 False Positive Management Checklist
- Identify recurring false positive pattern
- Verify activity is truly legitimate
- Document business justification
- Create suppression rule with narrowest scope
- Set review/expiration date
- Monitor suppression impact
- Review exceptions on schedule
- Update or remove stale exceptions
What's Next?
| Guide | Description |
|---|---|
| Custom Detection Rules | Create custom rules for your environment |
| Investigating Events | Validate security alerts effectively |
| Threat Detection | Understand how threat detection works |