CAS-004 Security Operations Practice Question
A security team is implementing a new detection rule in their SIEM to identify brute-force attacks against a web application. The rule should trigger when there are more than 10 failed login attempts from the same source IP within 5 minutes. Which of the following data sources is MOST critical for this detection?
⚠ Common exam trap
The trap here is assuming that firewall or web server logs contain authentication results, when they typically do not.
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
✓
Application authentication logs
To detect brute-force attacks based on failed login attempts, the SIEM needs logs that record authentication failures. Application authentication logs provide this information with sufficient detail (source IP, timestamp, outcome). Other sources either lack authentication context or are derived alerts, making them less suitable for building a precise correlation rule.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Application authentication logs
Why this is correct
Application authentication logs capture login attempts and their outcomes, including failures. They provide the necessary details such as username, source IP, and timestamp to detect brute-force patterns. This is the most critical source for identifying failed logins within a time window.
- ✗
Intrusion detection system (IDS) alerts
Why it's wrong here
IDS alerts may include signatures for brute-force attacks, but they are not a primary data source for detection rules. They are generated after detection and may not provide the granular failed login counts needed for custom correlation. The SIEM rule should be based on raw logs, not alerts.
- ✗
Firewall logs
Why it's wrong here
Firewall logs show allowed or denied network connections but do not indicate whether a login attempt succeeded or failed. They can show repeated connections to the login port but lack authentication context. Thus, they cannot reliably detect brute-force attacks based on failed logins.
- ✗
Web server access logs
Why it's wrong here
Web server access logs record HTTP requests but typically do not include authentication success or failure details. They may show POST requests to login endpoints but not the outcome. Therefore, they are insufficient for detecting failed login attempts, which require application-level logging.
Go deeper
Related to this question
About these practice questions
One of 973 original CAS-005 practice questions on Courseiva, each with a full explanation and wrong-answer analysis — not exam dumps or protected exam content. Learn why practice questions differ from exam dumps →
JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official CompTIA exam blueprint
This CAS-005 practice question is part of Courseiva's free CompTIA 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 CAS-005 exam.