The pcntl_exec implementation in PHP before 5.4.41, 5.5.x before 5.5.25, and 5.6.x before 5.6.9 truncates a pathname upon encountering a \x00 character, which might allow remote attackers to bypass intended extension restrictions and execute files with unexpected names via a crafted first argument.  NOTE: this vulnerability exists because of an incomplete fix for CVE-2006-7243.