The Web Application Hacker’s Handbook Discovering and Exploiting Security Flaws

When a breakpoint is hit, review the call stack to identify any relevant

data being passed to the function — in particular, any user-supplied data

that is being subjected to validation. By tracing the path of this data,

attempt to understand the processing being performed on it.

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It is often easy to use a debugger to subvert the execution path of a

process in useful ways — for example, by modifying the parameters on

the stack being passed as inputs to a function, modifying the EAX regis-

ter used to pass the return value back from a function, or rewriting key

instructions like comparisons and jumps to change the logic imple-

mented within a function. If possible, use these techniques to circumvent

validation controls, causing potentially malicious data to be accepted for