Whats an INPUT element?
INPUT elements are used to enable a user to input data into a web form. Web forms can gather input through many different methods – via text boxes, drop-down boxes, etc. The web developer specifies in the HTML code exactly what method will be used, by selecting a value for one attribute of the INPUT element known as TYPE. For instance, if TYPE is set to CHECKBOX, the input will be gathered via a checkbox; if it’s set to BUTTON, the input will be gathered via a button selection. This vulnerability involves how INPUT elements operate when TYPE is set to FILE.