mod_access_referer -- null pointer dereference vulnerability

A malformed Referer header field causes the Apache
ap_parse_uri_components function to discard it with the
result that a pointer is not initialized. The
mod_access_referer module does not take this into account
with the result that it may use such a pointer.
The null pointer vulnerability may possibly be used in a
remote denial of service attack against affected Apache
servers.