Apache httpd 2.0.59 and 2.2.4, with the Prefork MPM module, allows local users to cause a denial of service via certain code sequences executed in a worker process that (1) stop request processing by killing all worker processes and preventing creation of replacements or (2) hang the system by forcing the master process to fork an arbitrarily large number of worker processes.  NOTE: This might be an inherent design limitation of Apache with respect to worker processes in hosted environments.