GCFA Enterprise Environment Incident Response Practice Question
During a response to an incident involving a web shell, you find that the attacker is using custom encoding to bypass WAF signatures. What is the best forensic approach to identify all impacted web files?
⚠ Common exam trap
Candidates often choose WAF log analysis, assuming the WAF will catch all attempts. However, custom encoding bypasses signatures, making file-level integrity checking the only reliable way to detect injected code.
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
✓
Perform a file integrity check against the original source code base.
When attackers use custom encoding to hide web shells, signature-based WAF detections are ineffective. The most robust method is to perform a differential analysis of the web application's codebase against a known-good baseline, such as the original source control repository. By automatically highlighting differences, you can identify injected code blocks that don't match authorized files, regardless of how they are encoded or obfuscated by the attacker during the injection process.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Run a regex-based search for common web shell function names.
Why it's wrong here
Regex searches for functions like 'eval' or 'base64_decode' fail when the attacker uses custom encoding or advanced obfuscation techniques. The attacker can easily rename variables or use alternative encoding schemes that bypass standard keyword-based detection, making this method unreliable for finding sophisticated or obfuscated malicious code in large web directories.
- ✓
Perform a file integrity check against the original source code base.
Why this is correct
Comparing the current web directory against a trusted source control baseline is the most effective way to detect unauthorized modifications. By identifying every added, deleted, or modified file, you can isolate the web shells regardless of their obfuscation, as any unauthorized change is inherently suspicious in a production environment.
- ✗
Analyze WAF logs to identify all requests that resulted in 200 OK codes.
Why it's wrong here
WAF logs are useful, but they only record requests made to the server. If the attacker uploaded the shell through a compromised developer account or a separate vulnerability, the WAF logs may not show the initial file creation. Furthermore, a large volume of 200 OK responses is normal for web traffic.
- ✗
Examine the access logs for all requests containing encoded characters.
Why it's wrong here
Access logs are not suitable for identifying the presence of a web shell on the server. While they show the requests made, they do not tell you if the request successfully created or modified a file on the disk. Furthermore, many legitimate web applications use encoded characters for dynamic content.
About these practice questions
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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 GIAC exam blueprint
This GCFA practice question is part of Courseiva's free GIAC 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 GCFA exam.