The move_uploaded_file implementation in ext/standard/basic_functions.c in PHP before 5.4.39, 5.5.x before 5.5.23, and 5.6.x before 5.6.7 truncates a pathname upon encountering a \x00 character, which allows remote attackers to bypass intended extension restrictions and create files with unexpected names via a crafted second argument.  NOTE: this vulnerability exists because of an incomplete fix for CVE-2006-7243.