Original Post: WebSec — SSTI (Server Site Template Injection) | by Meryem Dalgalı | Aug, 2024
The content discusses Server Side Template Injection (SSTI) vulnerabilities in web applications, emphasizing the importance of understanding MVC (Model-View-Controller) architecture. It begins with an overview of MVC, which segregates application logic into three interconnected components: Model (data processing/storage), View (user interface), and Controller (workflow management). Ensuring code organization, MVC is often utilized in complex applications to handle frontend-backend interactions.
The document highlights the role of template engines (housed within the View layer) in rendering dynamic web pages by combining static templates with dynamic data from the Controller layer. Various template engines across different programming languages are cited, like Smarty for PHP or Jinja2 for Python.
The SSTI vulnerability arises when user-provided dynamic data is improperly processed within templates, enabling attackers to inject malicious code that executes server-side. The text outlines methods to detect SSTI, such as manipulating inputs to see if certain meta characters are processed.
For exploiting confirmed SSTI vulnerabilities, the process involves:
1. Reading documents to understand the scope
2. Exploring the environment to identify accessible objects (using provided properties and methods lists)
3. Executing attacks through arbitrary object creation, file read/write operations, and exploiting additional security weaknesses.
Example payloads and a generic cheatsheet for various template engines (like PHP and Python) assist in identifying and exploiting these vulnerabilities.
To prevent such vulnerabilities, advises include:
– Restricting user authorization to edit/add templates
– Regularly updating third-party web application components
– Input sanitization
– Using logic-less template engines (e.g., Mustache)
A code review section demonstrates securely handling user input in templates, illustrating secure coding practices to avoid SSTI. Recommended tools and further resources are also mentioned, but not detailed in the provided section.
Overall, the document serves as a comprehensive guide on understanding, detecting, exploiting, and mitigating SSTI vulnerabilities.
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