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    Response Processors: CSRF Processor: Incident - CSRF Parameter Tampering

    Complexity: Suspicious (1.0)

    Default Response: 10x = Multiple CSRF Parameter Tampering Incident.

    Cause: WebApp Secure protects against CSRF attacks by using a special interception technique. When a request comes in to WebApp Secure, the referer is checked. In the event that there is a third party referer (the user was following a link from another site), the interception mechanism kicks in. This involves returning a special page to the user that validates that the user is intentionally requesting the resource. If the validation is successful, the user is transparently redirected to the original resource they requested. If the validation fails, the user is then instructed to manually confirm their intentions, or return to the page they came from (to prevent the CSRF attack from working). In most cases, a valid CSRF attack would function in such a way as to hide this manual confirmation step, so the user would probably never see it (for example if the URL was loaded using an image HTML tag, then the resulting HTML confirmation step would not render, because its HTML, not an image). This incident is triggered when a user submits a request with a third party referer, and then manipulates the code of the CSRF interception page to alter the original data that was submitted. For example, they submit a request that looks like a CSRF attack (has a third party referer), and then use a tool like Firebug to edit the query string parameters that would be sent to the server after they manually allowed the request on the CSRF intercept page.

    Behavior: CSRF attacks are generally two-phase. The first phase involves the attacker establishing a functional CSRF attack. This could take quite a while and involves the attacker making requests to the protected site, trying all different types of CSRF techniques. The second phase is when the attacker injects the successful CSRF vector into a public website. In the second phase, legitimate users are visiting the public website and unknowingly executing the CSRF attack in the background. It is not useful to flag the victims of the CSRF attack as hackers, because they might not even know what is going on. However it is useful to flag the original attack vector establishment, because it can shed light on who created the "CSRF243"attack. This incident reflects a user who is manipulating the CSRF prevention mechanism, likely in an attempt to find a way to get around it.As such, if a user has this incident, they are probably trying to establish a CSRF attack, and careful attention should be paid to the values they are changing the parameters to and which URL is being requested (this will help identify what the user is trying to attack).

    Published: 2015-02-04