The Zend people have found a vulnerability in older
versions of PHP4 (the original advisory speaks of 4.0.4 while the bugs are
present in 4.0.3 as well). It is possible to specify PHP directives on a
per-directory basis which leads to a remote attacker crafting an HTTP request
that would cause the next page to be served with the wrong values for these
directives. Also even if PHP is installed, it can be activated and deactivated
on a per-directory or per-virtual host basis using the "engine=on" or
"engine=off" directive. This setting can be leaked to other virtual hosts on
the same machine, effectively disabling PHP for those hosts and resulting in
PHP source code being sent to the client instead of being executed on the
server.
