easyMultiple Choice
Tuning Snort Signatures to Reduce False Positives — Exceptions, Thresholds, IPs
An IDS generates an alert for a signature that matches HTTP traffic containing 'cmd.exe' in the URI. The analyst checks the packet and sees the URI is actually 'cmd.exe?help'. What should the analyst do?
⚠ Common exam trap
Cisco often tests the distinction between a false positive and a true positive, and the trap here is that candidates may assume any match for 'cmd.exe' is malicious, leading them to choose escalation or blocking instead of recognizing the need for signature tuning.
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
✓
Tune the signature to reduce false positives
The IDS signature triggered on the presence of 'cmd.exe' in the URI, but the actual traffic was 'cmd.exe?help', which is a legitimate help request and not an exploitation attempt. Tuning the signature to account for the query string reduces false positives without losing detection capability for actual attacks. This aligns with best practices for IDS management, where signatures are adjusted to match real threat patterns rather than exact strings.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Block the source IP
Why it's wrong here
Blocking the source IP treats a false positive as an attack, disrupting legitimate traffic that merely contains 'cmd.exe' as a query string. IP blocking suits confirmed malicious sources, such as a host repeatedly brute-forcing SSH, where containment outweighs disruption.
- ✓
Tune the signature to reduce false positives
Why this is correct
The URI 'cmd.exe?help' is benign query-string content, not malicious execution, so the signature's substring match is over-broad. Tuning it — for example requiring the executable in a command context rather than any URI — suppresses this recurring false positive while preserving detection of genuine 'cmd.exe' abuse.
- ✗
Disable the signature
Why it's wrong here
Disabling the signature removes detection of genuine cmd.exe URI attacks across the whole estate, not just this benign '?help' query. Signature tuning or exception rules suit recurring false positives on known-good parameters, preserving coverage for actual exploitation attempts.
- ✗
Escalate to incident response
Why it's wrong here
The signature matched a substring, and the trailing '?help' shows a benign query string rather than executable invocation, so no incident exists. Escalation suits confirmed compromise; here the analyst should tune or document the false positive instead.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-201 practice question is part of Courseiva's free Cisco 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 200-201 exam.