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CISM Practice Question: An organization's incident response team is…
An organization's incident response team is notified of a potential denial-of-service (DoS) attack targeting their web application. The team suspects a distributed denial-of-service (DDoS) attack. What is the FIRST step the team should take?
⚠ Common exam trap
The trap here is that candidates often jump to immediate mitigation (blocking IPs or shutting down) without first verifying the incident, but the CISM framework emphasizes that the first step in incident response is always to confirm and characterize the event before taking action.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Analyze network traffic to confirm the attack.
Before taking any action, the incident response team must first confirm that a DDoS attack is actually occurring. Analyzing network traffic (e.g., using NetFlow, sFlow, or packet capture) allows the team to distinguish a genuine DDoS from a flash crowd, a misconfiguration, or a legitimate spike in traffic. This step ensures that subsequent mitigation efforts are based on accurate evidence, preventing unnecessary disruption to services.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Contact the ISP to block the attacking IPs.
Why it's wrong here
Contacting the ISP presumes the attack originates from a fixed set of source addresses, but DDoS traffic is distributed across many compromised hosts, so blocking individual IPs leaves the flood intact. It is tempting because ISP-level filtering is effective against single-source DoS from one identifiable address.
- ✗
Shut down the web application to protect resources.
Why it's wrong here
Shutting down the application hands the attacker their objective and removes the service the team is defending, without confirming the attack or preserving forensic evidence. It is tempting because taking a targeted host offline is a valid containment step for a compromised server, where isolation stops data exfiltration.
- ✗
Implement rate limiting on the web server.
Why it's wrong here
Rate limiting is a mitigation applied after the incident is understood and declared; the first step is to validate the alert and begin the response process. It is tempting because rate limiting is a legitimate preventive control for throttling excessive requests from individual clients.
- ✓
Analyze network traffic to confirm the attack.
Why this is correct
Confirming the attack through traffic analysis distinguishes genuine volumetric or application-layer flooding from a false alarm before committing mitigation resources. Verification establishes the scope, source distribution and attack type, which determines whether scrubbing, rate limiting or upstream filtering is appropriate.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This CISM practice question is part of Courseiva's free ISACA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the CISM exam.