Web Cache Deception Attack

Tools

  • Param Miner - PortSwigger

    This extension identifies hidden, unlinked parameters. It's particularly useful for finding web cache poisoning vulnerabilities.

Exploit

  1. Browser requests http://www.example.com/home.php/non-existent.css.
  2. Server returns the content of http://www.example.com/home.php, most probably with HTTP caching headers that instruct to not cache this page.
  3. The response goes through the proxy.
  4. The proxy identifies that the file has a css extension.
  5. Under the cache directory, the proxy creates a directory named home.php, and caches the imposter "CSS" file (non-existent.css) inside.

Methodology of the attack - example

  1. Normal browsing, visit home : https://www.example.com/myaccount/home/
  2. Open the malicious link : https://www.example.com/myaccount/home/malicious.css
  3. The page is displayed as /home and the cache is saving the page
  4. Open a private tab with the previous URL : https://www.paypal.com/myaccount/home/malicous.css
  5. The content of the cache is displayed

Video of the attack by Omer Gil - Web Cache Deception Attack in PayPal Home Page DEMO

Methodology 2

  1. Find an unkeyed input for a Cache Poisoning 
    Values: User-Agent
Values: Cookie
Header: X-Forwarded-Host
Header: X-Host
Header: X-Forwarded-Server
Header: X-Forwarded-Scheme (header; also in combination with X-Forwarded-Host)
Header: X-Original-URL (Symfony)
Header: X-Rewrite-URL (Symfony)
  2. Cache poisoning attack - Example for X-Forwarded-Host unkeyed input (remember to use a buster to only cache this webpage instead of the main page of the website) 
    GET /test?buster=123 HTTP/1.1
Host: target.com
X-Forwarded-Host: test"><script>alert(1)</script>

HTTP/1.1 200 OK
Cache-Control: public, no-cache
[..]
<meta property="og:image" content="https://test"><script>alert(1)</script>">

References