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Web Cache Deception

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README.md

Web Cache Deception

Summary

Tools

  • PortSwigger/param-miner

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

Exploit

  1. Browser requests a resource such as 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 - Caching Sensitive Data

Example 1 - Web Cache Deception on PayPal Home Page

  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.example.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

Example 2 - Web Cache Deception on OpenAI

  1. Attacker crafts a dedicated .css path of the /api/auth/session endpoint.
  2. Attacker distributes the link
  3. Victims visit the legitimate link.
  4. Response is cached.
  5. Attacker harvests JWT Credentials.

Methodology - Caching Custom JavaScript

  1. Find an un-keyed 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 un-keyed 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>">

CloudFlare Caching

CloudFlare caches the resource when the Cache-Control header is set to public and max-age is greater than 0.

CloudFlare has a list of default extensions that gets cached behind their Load Balancers.
7Z CSV GIF MIDI PNG TIF ZIP
AVI DOC GZ MKV PPT TIFF ZST
AVIF DOCX ICO MP3 PPTX TTF CSS
APK DMG ISO MP4 PS WEBM FLAC
BIN EJS JAR OGG RAR WEBP MID
BMP EOT JPG OTF SVG WOFF PLS
BZ2 EPS JPEG PDF SVGZ WOFF2 TAR
CLASS EXE JS PICT SWF XLS XLSX

Labs

References