Some kind guy sent to me the next information. This WAS NOT revised or audited by the author, but it could help other people. So, enjoy!:

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mod_access_referer contains a null-pinter dereferences vulnerability that may possibly be used in denial of service attacks. While the impact of this vulnerability is considered low-risk, we advise you to apply the following patch:

--- mod_access_referer.c.org    Wed Apr  9 19:27:00 2003
+++ mod_access_referer.c        Wed Apr  9 19:36:20 2003
@@ -492,6 +492,10 @@
                                                         (r->headers_in,
                                                          "Referer"),
                                                         &uptr);
+                               if(uptr.hostname == NULL) {
+                                   return 0;
+                               }
+
                                if (!is_ip (uptr.hostname)) {
                                        /* XX resolv the domain name */
                                        got_refererhost_ip = 1;