mod_access_referer 1.0.2 allows remote attackers to cause a denial of service (crash) via a malformed Referer header that is missing a hostname, as parsed by the ap_parse_uri_components function in Apache, which triggers a null dereference.
http://www.vuxml.org/freebsd/af747389-42ba-11d9-bd37-00065be4b5b6.html
http://sourceforge.net/project/shownotes.php?release_id=151905
http://secunia.com/advisories/8612
http://lists.grok.org.uk/pipermail/full-disclosure/2003-April/004555.html