PHP before 5.3.4 accepts the \0 character in a pathname, which might allow context-dependent attackers to bypass intended access restrictions by placing a safe file extension after this character, as demonstrated by .php\0.jpg at the end of the argument to the file_exists function.
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.