The correct answer is to create a polyglot file that starts with JPEG magic bytes but contains PHP code at the end, and upload it with a .php extension. This technique works because the application validates file extensions and checks the MIME type by inspecting the file’s magic bytes—the first few bytes that identify a JPEG image—while ignoring the rest of the content. By embedding PHP code after the valid JPEG header, you bypass both the extension whitelist and the MIME type check, allowing the server to execute the PHP payload when the file is accessed. On the CompTIA PenTest+ PT0-002 exam, this scenario tests your understanding of polyglot file upload bypass as a common evasion method against server-side validation that only scans file headers. A frequent trap is assuming that changing the extension to .php.jpg will work, but whitelists typically reject double extensions. Remember the memory tip: “Magic bytes fool the front, PHP code hides in the back.”
PT0-002 Tools and Code Analysis Practice Question
This PT0-002 practice question tests your understanding of tools and code analysis. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
You are performing a web application penetration test for a client that uses a custom content management system (CMS). During the initial reconnaissance, you identify that the CMS has a file upload feature that accepts JPEG images. You suspect that the application may be vulnerable to unrestricted file upload, allowing you to upload a malicious PHP script to gain remote code execution. However, the application validates file extensions and checks the MIME type of the uploaded file. You have access to Burp Suite and a Python environment. Which of the following approaches is most likely to successfully bypass the file upload restrictions and achieve remote code execution?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create a polyglot file that starts with JPEG magic bytes but contains PHP code at the end, and upload with a .php extension
Option B is correct because appending PHP code to a valid JPEG image (polyglot) can bypass MIME type checks and extension filters if the application only inspects the magic bytes. Option A is wrong because changing the extension to .php.jpg will likely be rejected by the extension whitelist. Option C is wrong because curl's --data-binary is not designed for file upload with multipart/form-data. Option D is wrong because base64 encoding the payload does not change the content type and will still be detected as PHP.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Change the file extension to .php.jpg and submit using Burp Repeater
Why it's wrong here
Double extensions may bypass some filters, but the server likely checks the logical extension.
✗
Encode the PHP payload in base64 and submit it as a JPEG file
Why it's wrong here
Base64 encoding does not change the actual content type; the server will see non-JPEG data.
✗
Use curl with --data-binary to send a raw PHP payload with a proper JPEG content-type header
Why it's wrong here
The server will still validate the file extension and MIME type based on the content.
✓
Create a polyglot file that starts with JPEG magic bytes but contains PHP code at the end, and upload with a .php extension
Why this is correct
Polyglot files can pass MIME type checks while containing executable code.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A SOC analyst notices unusual lateral movement in the network at 2 AM. The IR playbook dictates: identify and contain (isolate the affected machine), then eradicate (remove the malware), then recover (restore from backup), then document. Skipping containment before eradication risks the attacker regaining access. Questions like this test the sequence and rationale of incident response phases.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this PT0-002 question in full detail.
Identify which PT0-002 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Tools and Code Analysis — This question tests Tools and Code Analysis — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Create a polyglot file that starts with JPEG magic bytes but contains PHP code at the end, and upload with a .php extension — Option B is correct because appending PHP code to a valid JPEG image (polyglot) can bypass MIME type checks and extension filters if the application only inspects the magic bytes. Option A is wrong because changing the extension to .php.jpg will likely be rejected by the extension whitelist. Option C is wrong because curl's --data-binary is not designed for file upload with multipart/form-data. Option D is wrong because base64 encoding the payload does not change the content type and will still be detected as PHP.
What should I do if I get this PT0-002 question wrong?
Identify which PT0-002 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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