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TheftFuzzer is a tool that fuzzes Cross-Origin Resource Sharing implementations for common misconfigurations. You can read the technique here.
Cross-origin resource sharing (CORS) is a mechanism that allows restricted resources on a web page to be requested from another domain outside the domain from which the first resource was served. A web page may freely embed cross-origin images, stylesheets, scripts, iframes, and videos. Certain “cross-domain” requests, notably Ajax requests, are forbidden by default by the same-origin security policy.
CORS defines a way in which a browser and server can interact to determine whether or not it is safe to allow the cross-origin request. It allows for more freedom and functionality than purely same-origin requests, but is more secure than simply allowing all cross-origin requests.

Download
git clone https://github.com/lc/theftfuzzer.git
Use
Source: https://github.com/lc/