IDS Alert Investigation

IDS alerts identify potential threats, but alerts require investigation to determine whether genuine attacks occurred. Effective investigation correlates IDS data with other sources to understand what really happened.

Alert Triage

Severity assessment - Initial prioritization based on rule classification, target criticality, and threat intelligence.

Alert clustering - Multiple related alerts might represent one incident. Group by source, destination, or time window.

Quick validation - Can you immediately determine if this is a known false positive? Documented suppression cases help.

Investigation Process

Examine signature - Understand what the rule detects. Read the rule and reference materials. What attack does it indicate?

Analyze payload - If packet capture is available, examine the actual traffic. Does it match expected attack characteristics?

Check target context - Is the target potentially vulnerable? A Windows attack against a Linux server is low risk.

Source analysis - What is the source? External attacker? Internal system? Is there history of similar alerts?

Correlation with Other Sources

Endpoint data - Did the target show signs of exploitation? Check EDR for suspicious processes, file drops, or behavior.

Network data - What other traffic occurred between these endpoints? Was there data exfiltration?

Authentication logs - Did compromised credentials grant access? Check for suspicious logons.

Asset context - What is the target system? What data does it hold? Who uses it?

Common Alert Scenarios

True positive confirmed - Attack evidence on both network and endpoint. Proceed to incident response.

Blocked attack - IDS detected attack, but defenses prevented impact. Document and close, verify blocking controls worked.

False positive - Investigation reveals legitimate activity matching detection patterns. Document for tuning.

Inconclusive - Cannot determine definitively. May require escalation or monitoring for additional indicators.

Documentation

Record investigation findings:

• What alerts were analyzed


• What evidence was examined


• What determination was made


• Why that conclusion was reached


• What follow-up actions are needed

Good documentation enables review, supports learning, and guides future tuning.