SSRF

SSRF (Server Side Request Forgery) is a vulnerability that allows an attacker to force a server to issue requests on their behalf. This can be used to access internal resources, scan ports, and more.

For example, consider a web application that allows users to upload images. The application might fetch the image from a URL provided by the user. If the application does not properly validate the URL, an attacker could provide a URL that points to an internal resource, such as http://localhost/admin, and the server would fetch that resource on behalf of the attacker.

Consider the following example:

import requests

def fetch_url(url):
    response = requests.get(url)
    return response.text

url = input('Enter a URL: ')
print(fetch_url(url))

If the application does not properly validate the URL, an attacker could provide a URL like http://localhost/admin and the server would fetch the admin page and return it to the attacker.