Hacking 🛡 Web Cache Deception Vulnerability: Exploitation & Data Leakage Prevention

[dEEpEst]

🛡 Web Cache Deception Vulnerability: Exploitation & Data Leakage Prevention

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Post created for the Hack Tools Dark Community — join the discussion below

What is Caching?
Caching is a performance technique used to store copies of content for faster access and reduced server load. Common systems include:

• Content Delivery Networks (CDNs)
• Reverse Proxies
• Load Balancers

What is Web Cache Deception (WCD)?
Web Cache Deception is a vulnerability that tricks caching systems into storing personalized content (e.g. user account data) as public resources — exposing sensitive data to any visitor.

How It Works:

1. An authenticated user accesses a private endpoint like `/account`
2. An attacker appends a fake file extension to the path: `/account.css`
3. If the server still returns sensitive content (despite the misleading extension)...
4. ...the caching layer might treat it as static content and store it.
5. Future visitors to `/account.css` receive the cached sensitive data.

Root Causes:

• Weak validation of file extensions in URLs.
• Cache system unaware of user session state (missing `Vary: Cookie` or `Authorization`).
• Missing `Cache-Control: no-store` on sensitive pages.
• Server renders sensitive content even on nonsensical paths like `.jpg`, `.css`.

Pentesting Methodology:

• Target authenticated-only pages like `/account`, `/profile`, `/dashboard`
• Append extensions like `.css`, `.jpg`, `.pdf`, `.json` (e.g., `/account.css`)
• 👁 Monitor server response — does it leak user info?
• Open link in incognito/private window — if the same content appears, it’s a hit.
• Analyze HTTP response headers — focus on `Cache-Control`, `Vary`, and `Content-Type`

Recommended Tools:

• Burp Suite: Use Repeater & Interceptor
• Param Miner: Burp extension for cache-poisoning discovery
• curl / httpie: Analyze headers easily
  curl -I https://example.com/account.css

🛡 Prevention Strategies for Developers:

• Set Cache-Control: no-store, private on sensitive routes
• Validate requested file extensions strictly
• Check session state before rendering sensitive data
• Add Vary: Cookie or Vary: Authorization headers to control cache behavior

Summary:
Web Cache Deception exploits architectural misunderstandings between dynamic content and caching logic. It bypasses traditional defenses and leaks data with minimal effort.

Even without SQLi or XSS, this vulnerability proves that improper cache handling can be as devastating as classic injection attacks.

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What’s your experience with WCD? Have you found it in the wild or protected against it in production? Share your insights below.