PHP 4.x and 5.x before 5.2.1, when running on multi-threaded systems, does not ensure thread safety for libc crypt function calls using pro…

PHP 4.x and 5.x before 5.2.1, when running on multi-threaded systems, does not ensure thread safety for libc crypt function calls using protection schemes such as a mutex, which creates race conditions that allow remote attackers to overwrite internal program memory and gain system access.