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109 lines
5.0 KiB
Markdown
109 lines
5.0 KiB
Markdown
# Web Cache Deception
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## Summary
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* [Tools](#tools)
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* [Exploit](#exploit)
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* [Methodology - Caching Sensitive Data](#methodology---caching-sensitive-data)
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* [Methodology - Caching Custom JavaScript](#methodology---caching-custom-javascript)
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* [CloudFlare Caching](#cloudflare-caching)
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* [Labs](#labs)
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* [References](#references)
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## Tools
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* [PortSwigger/param-miner](https://github.com/PortSwigger/param-miner)
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> This extension identifies hidden, unlinked parameters. It's particularly useful for finding web cache poisoning vulnerabilities.
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## Exploit
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1. Browser requests a resource such as `http://www.example.com/home.php/non-existent.css`.
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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.
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3. The response goes through the proxy.
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4. The proxy identifies that the file has a css extension.
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5. Under the cache directory, the proxy creates a directory named home.php, and caches the imposter "CSS" file (non-existent.css) inside.
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### Methodology - Caching Sensitive Data
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**Example 1** - Web Cache Deception on PayPal Home Page
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1. Normal browsing, visit home : `https://www.example.com/myaccount/home/`
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2. Open the malicious link : `https://www.example.com/myaccount/home/malicious.css`
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3. The page is displayed as /home and the cache is saving the page
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4. Open a private tab with the previous URL : `https://www.example.com/myaccount/home/malicous.css`
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5. The content of the cache is displayed
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Video of the attack by Omer Gil - Web Cache Deception Attack in PayPal Home Page
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[](https://vimeo.com/249130093)
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**Example 2** - Web Cache Deception on OpenAI
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1. Attacker crafts a dedicated .css path of the `/api/auth/session` endpoint.
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2. Attacker distributes the link
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3. Victims visit the legitimate link.
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4. Response is cached.
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5. Attacker harvests JWT Credentials.
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### Methodology - Caching Custom JavaScript
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1. Find an un-keyed input for a Cache Poisoning
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```js
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Values: User-Agent
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Values: Cookie
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Header: X-Forwarded-Host
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Header: X-Host
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Header: X-Forwarded-Server
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Header: X-Forwarded-Scheme (header; also in combination with X-Forwarded-Host)
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Header: X-Original-URL (Symfony)
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Header: X-Rewrite-URL (Symfony)
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```
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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)
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```js
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GET /test?buster=123 HTTP/1.1
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Host: target.com
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X-Forwarded-Host: test"><script>alert(1)</script>
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HTTP/1.1 200 OK
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Cache-Control: public, no-cache
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[..]
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<meta property="og:image" content="https://test"><script>alert(1)</script>">
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```
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## CloudFlare Caching
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CloudFlare caches the resource when the `Cache-Control` header is set to `public` and `max-age` is greater than 0.
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- The Cloudflare CDN does not cache HTML by default
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- Cloudflare only caches based on file extension and not by MIME type: [cloudflare/default-cache-behavior](https://developers.cloudflare.com/cache/about/default-cache-behavior/)
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CloudFlare has a list of default extensions that gets cached behind their Load Balancers.
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|-------|------|------|------|------|-------|------|
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| 7Z | CSV | GIF | MIDI | PNG | TIF | ZIP |
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| AVI | DOC | GZ | MKV | PPT | TIFF | ZST |
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| AVIF | DOCX | ICO | MP3 | PPTX | TTF | CSS |
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| APK | DMG | ISO | MP4 | PS | WEBM | FLAC |
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| BIN | EJS | JAR | OGG | RAR | WEBP | MID |
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| BMP | EOT | JPG | OTF | SVG | WOFF | PLS |
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| BZ2 | EPS | JPEG | PDF | SVGZ | WOFF2 | TAR |
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| CLASS | EXE | JS | PICT | SWF | XLS | XLSX |
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## Labs
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* [PortSwigger Labs for Web cache deception](https://portswigger.net/web-security/all-labs#web-cache-poisoning)
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## References
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* [Web Cache Deception Attack - Omer Gil](http://omergil.blogspot.fr/2017/02/web-cache-deception-attack.html)
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* [Practical Web Cache Poisoning - James Kettle @albinowax](https://portswigger.net/blog/practical-web-cache-poisoning)
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* [Web Cache Entanglement: Novel Pathways to Poisoning - James Kettle @albinowax](https://portswigger.net/research/web-cache-entanglement)
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* [Web Cache Deception Attack leads to user info disclosure - Kunal pandey - Feb 25](https://medium.com/@kunal94/web-cache-deception-attack-leads-to-user-info-disclosure-805318f7bb29)
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* [Web cache poisoning - Web Security Academy learning materials](https://portswigger.net/web-security/web-cache-poisoning)
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- [Exploiting cache design flaws](https://portswigger.net/web-security/web-cache-poisoning/exploiting-design-flaws)
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- [Exploiting cache implementation flaws](https://portswigger.net/web-security/web-cache-poisoning/exploiting-implementation-flaws)
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* [OpenAI Account Takeover - @naglinagli - Mar 24, 2023](https://twitter.com/naglinagli/status/1639343866313601024)
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* [Shockwave Identifies Web Cache Deception and Account Takeover Vulnerability affecting OpenAI's ChatGPT - Gal Nagli](https://www.shockwave.cloud/blog/shockwave-works-with-openai-to-fix-critical-chatgpt-vulnerability) |