1. A system comprising: a black-box tester comprising a hardware processor configured to interact with a web application during its execution to identify a web page exposed by the web application, the web application being hosted by a server and accessible by a client computer; a constraint manager configured to: receive the web page identified by the black-box tester; statically analyze the web page to identify a hidden parameter within the web page that is constrained by a client-side validation measure and that is to be sent to the web application, the hidden parameter to indicate an authorization level of a user of the client computer; and determine a server-side validation measure to be applied to the hidden parameter comprising the web application checking for a correlation between a value of the hidden parameter and a value of at least one other parameter from the user; and a static analyzer configured to: statically analyze the web application to identify a location within the web application where the hidden parameter is input into the web application; query the constraint manager for the server-side validation measure to be applied to the hidden parameter; determine whether the web application checks for the correlation between the value of the hidden parameter and the value of the least one other client-supplied parameter according to the server-side validation measure from the constraint manager prior to the hidden parameter being used in a security-sensitive operation; and identify the hidden parameter as a security vulnerability where the web application does not check for the correlation between the value of the hidden parameter and the value of the at least one other client-supplied parameter prior to the hidden parameter being used in the security-sensitive operation.