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    Response Processors: Request Captcha Processor: Incident - Mismatched Captcha Session

    Complexity: High (4.0)

    Default Response: 1x = Warn User, 2x = 5 Day Clear Inputs.

    Cause: A captcha is a special technique used to differentiate between human users, and automated scripts. This is done through a Turing test, where the user is required to visually identify characters in a jumbled image and transcribe them into an input. If the user is unable to complete the challenge in a reasonable amount of time, they are not allowed to proceed with their original request. Because it is nearly impossible to script the deciphering of the image, automated scripts generally get stuck and cannot proceed. Additionally, an audio version is optionally available to allow users who have a visual handicap to complete the captcha successfully. Captchas are used in two different ways by the system. They can be explicitly added to any workflow within the protected web application (such as requiring a captcha to login, or checkout a shopping cart), and they can be used to test a suspicious user before allowing them to continue using the site (similar to blocking the user, but with a way for the user to unblock themselves if they can prove they are not an automated script). Captchas are generally used to resolve "Insufficient Anti-Automation" weaknesses in the protected web application. Regardless of which type of captcha is being used, this incident is generated when the user provides a solution to a captcha that was issued for a different session then their own, as might be the case in a script that uses minimal human interaction to solve the captcha's, but everything else is automated

    Behavior: When a hacker is attempting to establish an automated script that is capable of defeating the captcha, they might use various different techniques. One of these techniques is to try and harvest successfully solves captchas from other users on the site. This can be done either by infecting those machines with a virus, or by implanting script into some of the sites pages (possibly through XSS). If this technique is used, then the captcha that is being solved might not have originated from the same session as the user who is submitting the solution. This is a dead giveaway that the user is attempting to defeat the captcha system to automate a specific task.

    Published: 2014-06-27