Exam CS0-003 topic 1 question 377 discussion

Nessus with restricted concurrent connections means configuring Nessus to limit the number of simultaneous connections it makes to the target systems during a scan. This is important for avoiding overwhelming sensitive systems, particularly in environments like critical infrastructure or ICS (Industrial Control Systems), where services may break or become unstable if they receive too many requests at once or requests that are too large.

The safest method to identify service versions in a fragile ICS (Industrial Control Systems) network is: C. Use nc to manually perform banner grabbing. ⸻ Explanation: ICS networks are highly sensitive, and many components can crash or malfunction if probed too aggressively. Therefore, low-impact, manual techniques are preferred over automated or intrusive scanners.

Safest Option: C -> Manually connects to a port (e.g., nc 192.168.1.1 80) and checks banners. No unexpected probes—avoids malformed requests. Low risk since it only reads initial service responses. Why D is a bad option, Nessus (Vulnerability Scanner with Throttling) Risk: Even with restricted connections, Nessus sends intrusive probes that could destabilize ICS devices. Use Case: Better for IT networks, not ICS.

C. Use nc (netcat) to manually perform banner grabbing Manually banner-grabbing with nc lets the analyst send a single, minimal request to each host and observe the returned service banner. Because the analyst fully controls the content and size of each probe, this approach avoids the malformed or high-volume traffic that can crash fragile ICS devices, making it the safest way to identify service versions in a critical-infrastructure network. Although limiting Nessus concurrency reduces volume, it does not eliminate the potentially harmful content of the probes. Manual banner grabbing is still the lowest-risk method for service-version discovery in sensitive ICS environments.

The best answer is D, as nessus is an automated tool that guarantees requests will not be malformed.

Nessus can be tuned for sensitive environments — and in some ICS contexts, it’s appropriate with the right care. But in terms of safest possible method, especially when you don’t know how fragile the systems are, the manual approach (nc) remains best.

Use Nessus with restricted concurrent connections.

Manual banner grabbing with netcat (nc) lets the analyst send minimal, carefully crafted inputs to elicit a service banner. This minimizes the risk of accidentally sending a request that could disrupt operations.