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# lab-2

## Basic Server-Side Template Injection (Code Context — Tornado)

**Difficulty:** Practitioner

### Lab Description

This lab is vulnerable to server-side template injection due to the unsafe use of a Tornado template.

**Objective:** Review the Tornado documentation to discover how to execute arbitrary code, then delete the `morale.txt` file from Carlos's home directory.

**Credentials:** `wiener:peter`

### Solution

**Step 1 — Look for a suspect parameter**

Since the lab description tells us the backend uses the **Tornado** template engine, we can test its syntax directly once a candidate parameter is found.

**Step 2 — Locate the injection point**

Go to **My account**, select an option under **Preferred name**, submit, and capture the request in Burp. A hidden parameter, `blog-post-author-display`, is revealed — this is the value used to display a name (first name, nickname, etc.) when posting a comment on a product. At this stage, SSTI isn't confirmed yet.

**Step 3 — Confirm template injection**

Set the parameter to:

```jinja
{{ 7*7 }}
```

URL-encode and send it. The current request/response doesn't reflect the result directly — but posting a *new* comment on a product afterward shows the output `49` rendered on the page, confirming SSTI.

**Step 4 — Enumerate available built-ins**

To find which dangerous functions are reachable, submit:

```jinja
{{ [k for k in __builtins__.keys() if any(x in k for x in ['exec', 'eval', 'system'])] }}
```

(Remember: a new comment must be posted each time to see the freshly rendered output.)

This returns:

```
['execfile', 'eval']
```

The presence of `execfile` confirms the backend is running **Python 2**, since this builtin was removed in Python 3.

**Step 5 — Exploit to delete the file**

Submit the following payload (URL-encoded) as a new comment to execute an OS command via `eval`:

```jinja
{{ __builtins__['eval']("__import__('os').popen('rm /home/carlos/morale.txt').read()") }}
```

### Conclusion

The Tornado template engine evaluated user-controlled input as code. By enumerating accessible Python builtins, an `eval`-based command execution primitive was found and used to delete the target file.


---

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