PHP 4.x to 4.3.9, and PHP 5.x to 5.0.2, when running in safe mode on a multithreaded Unix webserver, allows local users to bypass safe_mode_exec_dir restrictions and execute commands outside of the intended safe_mode_exec_dir via shell metacharacters in the current directory name.  NOTE: this issue was originally REJECTed by its CNA before publication, but that decision is in active dispute.  This candidate may change significantly in the future as a result of further discussion.