At the OWASP AppSec Europe, researchers demonstrated a very interesting otherwise underestimated issue. Although not a new attack category but quite dangerous if executed flawlessly. It exploits the fact how does your application behaves when receives multiple parameters with same name in same URL. For example, .../bank.php? action=view &accID=101& action=withdraw In URL above two one parameter 'action' has multiple occurrences with same name in same URL. What will the web application do? It can do one of the following depending on the environment it is using: It may only take the data from the first parameter It may take the data from the last parameter It may take the data from all parameters and concatenate them together Now we know that for the specific above URL the second action is quite dangerous! Using this technique even WAF (Web Application Firewall) can be evaded, it won't filter the request. Suppose a WAF is designed to detect and filter out attacks ...