The answer is `{{config.__class__.__init__.__globals__['os'].popen('id').read()}}` because it leverages Python object introspection to traverse from the template’s built-in `config` object up through the class hierarchy, accessing `__globals__` to reach the `os` module and execute system commands. This technique bypasses the template engine’s lack of sandboxing by exploiting Python’s dynamic object model, where every object exposes its class, initializer, and global namespace—allowing an attacker to chain attributes until they find a dangerous module like `os`. On the CompTIA PenTest+ PT0-002 exam, this tests your ability to recognize SSTI-to-RCE chains in Jinja2 or similar Python engines, often disguised among payloads that only read files or trigger errors. A common trap is choosing a payload that calls `eval()` or `exec()` directly, which may be blocked, while object introspection reliably navigates to `os.popen`. Memory tip: think “class, init, globals, os” as the four-step ladder to RCE.
PT0-002 Attacks and Exploits Practice Question
This PT0-002 practice question tests your understanding of attacks and exploits. 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.
During an internal test, a penetration tester discovers a web application that is vulnerable to Server-Side Template Injection (SSTI). The application uses a template engine that does not sandbox user input. Which of the following payloads would be MOST effective to achieve remote code execution on the server?
Option D is correct because it exploits Python's object model to access the `os` module via `__class__.__init__.__globals__`, bypassing the template engine's lack of sandboxing. This allows the attacker to execute arbitrary system commands like `id` on the server, achieving remote code execution (RCE). The payload is specific to Jinja2 or similar Python-based template engines that expose built-in objects.
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.
✗
{{7*7}}
Why it's wrong here
This is a simple math expression used to confirm SSTI vulnerability, but it does not achieve code execution.
✗
<script>alert('xss')</script>
Why it's wrong here
This is a cross-site scripting (XSS) payload, not applicable for SSTI code execution.
✗
${7*7}
Why it's wrong here
This expression works in some template engines (e.g., Java) for simple math, but does not provide RCE.
Correct. This payload exploits Python object chaining to execute system commands, achieving remote code execution.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates confuse SSTI with simple template injection tests (like `{{7*7}}`) or XSS, failing to recognize that the correct payload must chain object introspection to access system commands for RCE.
Detailed technical explanation
How to think about this question
In Jinja2, `__class__` accesses the class of a string object, `__init__` retrieves its constructor, `__globals__` exposes the global namespace of the module where the constructor was defined, often including imported modules like `os`. This technique works because Python's object model allows traversal of the inheritance chain to reach built-in functions, and template engines like Jinja2 do not restrict access to dunder methods by default. In real-world scenarios, this is commonly used against Flask applications where `config` is a global object available in templates.
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.
TExam Day Tips
→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 security team runs a vulnerability scan on a web application and discovers an unpatched SQL injection flaw. The team prioritises remediation by CVSS score — critical flaws are patched within 24 hours, high within 7 days. Questions like this test whether you understand vulnerability management processes, scanning tools, and remediation prioritisation.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this PT0-002 question in full detail.
Attacks and Exploits — This question tests Attacks and Exploits — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: {{config.__class__.__init__.__globals__['os'].popen('id').read()}} — Option D is correct because it exploits Python's object model to access the `os` module via `__class__.__init__.__globals__`, bypassing the template engine's lack of sandboxing. This allows the attacker to execute arbitrary system commands like `id` on the server, achieving remote code execution (RCE). The payload is specific to Jinja2 or similar Python-based template engines that expose built-in objects.
What should I do if I get this PT0-002 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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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