Cache key injection

Description

This lab contains multiple independent vulnerabilities, including cache key injection. A user regularly visits this site’s home page using Chrome.

Reproduction

  1. The redirect at /login excludes the parameter utm_content from the cache key using a flawed regex. This allows appending arbitrary unkeyed content to the lang parameter:

/login?lang=en?utm_content=fire

  1. The page at /login/ has an import from /js/localize.js. This is vulnerable to client-side parameter pollution via the lang parameter because it doesn’t URL-encode the value.

  2. The login page references an endpoint at /js/localize.js that is vulnerable to response header injection via the Origin request header, provided the cors parameter is set to 1.

  3. Use the Pragma: x-get-cache-key header to identify that the server is vulnerable to cache key injection, meaning the header injection can be triggered via a crafted URL.

  4. Combine these four behaviours by poisoning the cache with following two requests:

GET /js/localize.js?lang=en?utm_content=z&cors=1&x=1 HTTP/1.1
Origin: x%0d%0aContent-Length:%208%0d%0a%0d%0aalert(1)$$$$

GET /login?lang=en?utm_content=x%26cors=1%26x=1$$Origin=x%250d%250aContent-Length:%208%250d%250a%250d%250aalert(1)$$%23 HTTP/1.1

  1. This will poison /login?lang=en such that it redirects to a login page with a poisoned localization import that executes alert(1), solving the lab.

PoC

Exploitability

An attacker will need to combine the vulnerabilities to execute alert(1) in the victim’s browser. and make use of the Pragma: x-get-cache-key header in order to solve this lab.