Mozilla Firefox 1.5.0.4, 2.0.x before 2.0.0.8, Mozilla Suite 1.7.13, Mozilla SeaMonkey 1.0.2 and other versions before 1.1.5, and Netscape 8.1 and earlier allow user-assisted remote attackers to read arbitrary files by tricking a user into typing the characters of the target filename in a text box and using the OnKeyDown, OnKeyPress, and OnKeyUp Javascript keystroke events to change the focus and cause those characters to be inserted into a file upload input control, which can then upload the file when the user submits the form.
The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.