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

Methodology 2

1. Find an un-keyed input for a Cache Poisoning js 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 un-keyed input (remember to use a buster to only cache this webpage instead of the main page of the website) ```js GET /test?buster=123 HTTP/1.1 Host: target.com X-Forwarded-Host: test">

   HTTP/1.1 200 OK Cache-Control: public, no-cache [..] "> ```

References

• Web Cache Deception Attack - Omer Gil
• Practical Web Cache Poisoning - James Kettle @albinowax
• Web Cache Entanglement: Novel Pathways to Poisoning - James Kettle @albinowax
• Web Cache Deception Attack leads to user info disclosure - Kunal pandey - Feb 25
• Web cache poisoning - Web Security Academy learning materials
• Exploiting cache design flaws
• Exploiting cache implementation flaws

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Last update: August 30, 2022