Which Nmap Timing Template Safely Scans ICS Hosts for Insecure Ports?
A security analyst is scanning an ICS host (192.168.1.5) in an industrial plant for insecure ports while minimizing the impact to uptime or performance. Which of following commands should the analyst use to perform the task?
Community Insight
The exam tests Nmap timing templates in OT/ICS environments, and the trap is assuming Nmap's default -T3 is gentle enough for uptime-sensitive industrial equipment.
Scanning an ICS host for insecure services requires a slow Nmap timing template to protect uptime; this page confirms -T1 against FTP port 21 is the least disruptive correct choice.
Many learners choose option C because -T3 is Nmap's default 'normal' speed, but that pacing is still more aggressive than -T1 and can disrupt fragile ICS devices.
Community Discussion (4 comments)
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Expert Analysis
Why the Answer Is Correct
The question combines two constraints: identify an insecure port and choose an Nmap timing template that minimizes impact on an industrial control system. Option A uses -T1 (paranoid/sneaky) and targets port 21, which is FTP and is widely treated as an insecure cleartext service. Nmap's timing templates range from -T0/-T1 slowest and least intrusive to -T5 fastest and most aggressive, so -T1 best matches the uptime/performance requirement. Port 21 is a credible 'insecure port' target, making A the only option that satisfies both dimensions.Why the Other Options Are Wrong
Option B uses -T2 and port 3389 (RDP): -T2 is more polite than the default but still faster than -T1, and RDP is not the canonical insecure service the question is likely testing. Option C pairs -T3, Nmap's normal default, with SSH port 22; -T3 is too aggressive for many ICS devices and SSH is the secure replacement for Telnet, so it fails the 'insecure ports' wording. Option D uses -T5 (insane), the most aggressive template, against HTTP port 80, which directly conflicts with minimizing uptime impact. Thus B, C and D each fail at least one requirement.Community Comment Notes
rocco82 focuses on the insecure-port list, stating that ports 21 and 80 are insecure and favoring minimal impact with -T1. RUE_BOT reinforces the OT rationale, describing -T1 as "a much slower, lower-impact timing template" than -T2, -T3, or -T5. Pochex argues for -T3 as a "balanced" default, which captures the common but risky assumption that normal Nmap pacing is safe for ICS equipment. rvln7 also rejects port 22 because SSH is the secure replacement for Telnet and does not fit the insecure-port requirement.Official Reference
Exam Strategy
When an item mentions ICS/OT uptime, map the requirement to Nmap's slowest timing template before evaluating ports; then eliminate options whose ports do not match 'insecure' or whose timing is aggressive. Look for -T1 as the low-impact choice and avoid -T5 in any uptime-sensitive scenario.
Frequently Asked Questions
Why is -T3 not appropriate for an ICS host even though it is Nmap's default?
ICS/OT devices often cannot tolerate normal scan pacing; -T3 is more aggressive than -T1 'sneaky' and raises disruption risk.
Why is port 22 not a valid insecure port in this scenario?
Port 22 is SSH, an encrypted remote-admin service, so it does not match the question's insecure-port requirement; FTP port 21 does.