Hacking 🛡 What is SSTI Vulnerability? 🌐

[dEEpEst]

🛡 What is SSTI Vulnerability?

This post was created for the Hack Tools Dark Community

Server-Side Template Injection (SSTI) is one of the most dangerous vulnerabilities in modern web applications. It arises when user input is insecurely handled by a server-side template engine, potentially allowing attackers to execute arbitrary code.

Understanding SSTI:

How Template Engines Work:
Template engines dynamically render web pages by combining:
⏺ Static Page Structure: HTML/CSS skeleton.
⏺ Dynamic Server Data: Inserted into the page based on user/session.

Popular Template Engines:
Jinja2 (Python)
Twig (PHP)
ERB (Ruby)
Freemarker (Java)

How SSTI Happens

SSTI occurs when an application directly injects unsanitized user input into templates. Instead of treating the input as text, the template engine interprets it as code and executes it.

SSTI Requires:
⏺ Direct User Input in Template Code: e.g. username passed into `{{ username }}`
⏺ Lack of Input Sanitization: Special characters like `{{ }}` or `${}` are not neutralized.
⏺ Ability to Inject Template Syntax: Attacker can inject code that gets executed.

Example SSTI Payloads:
RCE Example (Jinja2):
{{ ''.__class__.__mro__[1].__subclasses__()[408]("rm -rf /", shell=True) }}

File Read Example:
{{_self.env.registerUndefinedFilterCallback("system")}}{{_self.env.getFilter("cat /etc/passwd")}}

SSTI Risks:
Remote Code Execution (RCE): Full command execution on the server.
Sensitive File Access: Read /etc/passwd, config files, DB credentials.
Privilege Escalation: Gain root/system-level access.

️ How to Detect SSTI:
Basic Tests:
⏺ Inject {{7*7}} or ${7*7} and check for `49` in the response.

Tools:
⏺ tplmap: Automated SSTI scanner/exploiter.
⏺ Burp Suite: To intercept and test payload injection in real traffic.

🛡 Mitigation & Prevention:

Safe Design Practices:
⏺ Strictly separate code logic from user data.
⏺ Use template engines that don’t allow logic execution (logic-less templates).

Sanitize Inputs:
⏺ Apply whitelists to limit what users can submit.
⏺ Strip special template symbols like `{}`, `${}`, `<%`, etc.

Technical Defenses:
⏺ Run templates in sandboxed environments.
⏺ Regularly update template engine libraries.
⏺ Disable dangerous features (e.g., expression evaluation).

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Disclaimer:

This post is intended **strictly for educational and ethical research purposes only**. The information provided here aims to raise awareness about web application vulnerabilities such as Server-Side Template Injection (SSTI) and help developers, security researchers, and system administrators understand and mitigate security flaws.

Unauthorized testing or exploitation of live systems without explicit permission is illegal and unethical. The author and the Hack Tools Dark Community are **not responsible for any misuse or damages** resulting from the application of the techniques discussed.

Always test in controlled environments or with proper authorization.

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This post was created for the Hack Tools Dark Community

If you've encountered SSTI in real-world apps, share your payloads, detection tricks, or mitigation tips below! Let's discuss advanced exploitation and defensive countermeasures.