6️⃣Server-Side Request Forgery (SSRF)

Explore our comprehensive article on Server-Side Request Forgery (SSRF), offering insightful information about this web security vulnerability, its potential impact, and measures for prevention.

What is Server-Side Request Forgery (SSRF)?

Server-side request Forgery (SSRF) is a security vulnerability that allows an attacker to induce a server-side application to make HTTP requests to an unintended location. This can enable various attacks, such as accessing internal services within the organization's infrastructure or leveraging the server's capability to carry out actions on behalf of the attacker.

How Does SSRF Work?

To exploit SSRF, an attacker finds an input within an application that is used to fetch resources from another server. The attacker then modifies the destination URL to an internal system that the server can access but the attacker cannot. The underlying server, executing the request, may inadvertently access or manipulate private data.

Consequences of SSRF Attacks

The impact of SSRF attacks can range from information disclosure to complete compromise of the system, depending on the nature of the internal services that are exposed. For instance, if an SSRF attack allows access to cloud service metadata endpoints, it could lead to the leakage of sensitive credentials.

Mitigation Strategies

To protect against SSRF attacks, developers should:

• Validate and sanitize user-supplied URLs rigorously.

• Implement strict access controls and network restrictions.

• Avoid passing untrusted input directly to internal services/APIs.

Using such mitigations can reduce the vector of SSRF attacks significantly.

Example of a Vulnerable Code to SSRF

In a web application, assume there is a feature that allows fetching a URL provided by the user:

from flask import Flask, request, redirect
import requests

app = Flask(__name__)

@app.route('/fetch', methods=['GET'])
def fetch_url():
    url = request.args.get('url')
    response = requests.get(url)
    return response.content

if __name__ == "__main__":
    app.run()

This example code in Python using Flask does not validate or sanitize the user input, making it vulnerable to SSRF.

Demonstrating an SSRF Attack

An attacker could exploit the above SSRF vulnerability by passing an internal or sensitive URL:

http://example.com/fetch?url=http://internal-service.secret/api/data