How to Read and Analyze Log Files for CySA+ Exam

If you are preparing for the CompTIA CySA+ (CS0-03) exam, you already know that log analysis is the beating heart of a Security Operations Center (SOC). Real-world security analysts don’t just stare at clean dashboards all day; they hunt through raw log files, error messages, and event histories to catch malicious actors red-handed.

For the CySA+ exam, you will be expected to interpret different types of logs, understand what normal behavior looks like versus an anomaly, and spot indicators of compromise (IoCs). In this guide, we will break down the essential logs you need to master, how to read them, and how to apply this knowledge to pass your exam.

Why Log Analysis Matters for CySA+

In almost every CompTIA CySA+ practice test and on the real exam itself, you will encounter scenarios where you are given a snippet of a log file and asked to identify the attack vector. Whether it’s a brute-force attempt, a web injection, or unauthorized lateral movement, the answer is always hidden in the logs.

As a Blue Team analyst, your primary tools include SIEM (Security Information and Event Management) systems that aggregate logs from multiple sources:

1. Firewalls and Routers: Network-level traffic and perimeter defense.
2. Web Servers (Apache, IIS): Application-layer attacks and HTTP requests.
3. Operating Systems (Windows Event Logs / Linux Syslog): Host-based activities, authentication attempts, and process execution.

1. Decoding Firewall Logs (Network Traffic)

Firewall logs track what traffic is allowed or blocked entering and leaving a network. On the exam, you need to spot outbound connections to suspicious external IP addresses or unusual ports.

Example Scenario:

Aug 18 10:12:35 firewall-01 kernel: [BLOCKED] IN=eth0 OUT=eth1 SRC=192.168.1.50 DST=203.0.113.45 PROTO=TCP SPT=49211 DPT=4444 WINDOW=64240 RES=0x00 ACK URGP=0

How to Analyze It:

• SRC (Source IP): 192.168.1.50 belongs to an internal corporate workstation.
• DST (Destination IP): 203.0.113.45 is an external IP address.
• DPT (Destination Port): Port 4444. This is a classic hallmark of a Metasploit Meterpreter reverse shell or other command-and-control (C2) communication. If an internal machine is trying to talk outbound on port 4444, investigate that endpoint immediately for malware or unauthorized execution.

2. Interpreting Web Server Logs (IIS / Apache)

Web applications are constantly targeted by SQL injection (SQLi), Cross-Site Scripting (XSS), and directory traversal attacks. Web server access logs record every HTTP request made to the server.

Example Scenario:

192.168.10.15 - - [18/Aug/2026:11:05:22 +0000] "GET /catalog.php?item=5' UNION SELECT 1,username,password FROM users-- HTTP/1.1" 200 4520

How to Analyze It:

• The Request URL: Look closely at the query string: item=5' UNION SELECT 1,username,password FROM users--.
• The Threat: This is a classic SQL Injection (SQLi) attack payload. The attacker is trying to break out of the standard SQL query logic (5') and append a malicious UNION SELECT statement to dump sensitive table data (usernames and passwords) from the database backend.
• Response Code: The 200 status code at the end indicates that the server successfully processed the request, which suggests the application is vulnerable and may have just leaked data.

3. Understanding Windows Event Logs

Host-based analysis is heavily tested on CySA+. Windows logs millions of events, but you only need to focus on key Event IDs that signal security incidents:

• Event ID 4624: An account was successfully logged on.
• Event ID 4625: An account failed to log on (watch out for a high frequency of these from a single IP, indicating a brute-force attack).
• Event ID 4688: A new process has been created (useful for tracking if PowerShell executed a malicious script).
• Event ID 1102: The audit log was cleared (a massive red flag indicating an attacker is trying to cover their tracks).

Example Scenario (Brute-Force Detection):

If you see hundreds of Event ID 4625 entries within a 2-minute window targeting the Administrator account from the same source workstation, you are looking at an active credential-stuffing or brute-force attack.

Recommended Study Resources & Books

To master log parsing, SIEM querying languages (like Splunk SPL or KQL), and threat detection frameworks, having a comprehensive study guide is essential.

Recommended Textbook:

• CompTIA CySA+ Cybersecurity Analyst Certification All-in-One Exam Guide (Exam CS0-03) by Fernando Maymí .
  • Why it’s great: This book dedicates extensive chapters to security operations, log parsing methodologies, and practical tools used by SOC analysts daily.

Practice Tests :

• YouTube Practice Tests (50-Scenario Based Questions): Reading log files in a book is different from analyzing them under exam pressure. Head over to our YouTube channel to access full 50-question practice tests specifically designed for CySA+ CS0-03.)

Summary Checklist for Log Analysis on CySA+

1. Know your ports: Memorize standard ports (HTTP 80, HTTPS 443, DNS 53, SSH 22, RDP 3389) and suspicious outliers (like 4444 or 1337).
2. Spot attack signatures: Look for anomalous characters in URLs (--, ', <script>, ../) indicating SQLi, XSS, or directory traversal.
3. Trace the timeline: Always correlate logs across firewalls, web servers, and Windows event logs to build a complete timeline during an incident response scenario.