SSRF Vulnerability Auditing - OWASP Top 10

Introduction

Server-Side Request Forgery (SSRF) is a security vulnerability that allows an attacker to send crafted requests from the server-side application to internal or external resources. This can lead to various attacks, including data theft and server compromise.

What is SSRF?

SSRF occurs when a web application is tricked into making requests to unintended destinations. This can happen when user input is used to construct requests without adequate validation or sanitization.

How SSRF Works

The attacker manipulates the input parameters of the application to direct the server to make requests to different endpoints. For example, if an application fetches user profile data from a URL provided by the user, the attacker could input a value that points to a sensitive internal service.

# Example of a vulnerable code snippet in Node.js
const axios = require('axios');

app.get('/fetch-user', (req, res) => {
    const userUrl = req.query.url; // This input is not validated
    axios.get(userUrl)
        .then(response => res.send(response.data))
        .catch(err => res.status(500).send(err));
});
            

Auditing Process

To effectively audit for SSRF vulnerabilities, follow these steps:

1. Identify user-controlled input points that make HTTP requests.
2. Check if the input is validated and sanitized.
3. Test for SSRF by crafting payloads pointing to internal services.
4. Review application logs for any unusual request patterns.

graph TD;
    A[Identify User Input] --> B[Check Validation]
    B --> C{Is Input Validated?}
    C -- Yes --> D[Secure Application]
    C -- No --> E[Test for SSRF]
    E --> F[Review Logs]
        

Best Practices

Implement the following best practices to mitigate SSRF vulnerabilities:

• Validate and sanitize all user inputs.
• Implement a whitelist of allowed URLs and IP ranges.
• Use a secure proxy to handle outbound requests.
• Disable unnecessary network protocols and services.
• Log and monitor outgoing requests for unusual patterns.

FAQ