Index: modules/proxy/mod_proxy.c
===================================================================
--- httpd-2.2.21/modules/proxy/mod_proxy.c	(revision 1179633)
+++ httpd-2.2.21/modules/proxy/mod_proxy.c	(working copy)
@@ -566,6 +566,13 @@
         return OK;
     }
 
+    /* Check that the URI is valid. */
+    if (!r->uri  || r->uri[0] != '/') {
+        ap_log_rerror(APLOG_MARK, APLOG_ERR, 0, r,
+                     "Invalid URI in request %s", r->the_request);
+        return HTTP_BAD_REQUEST;
+    }
+
     /* XXX: since r->uri has been manipulated already we're not really
      * compliant with RFC1945 at this point.  But this probably isn't
      * an issue because this is a hybrid proxy/origin server.
Index: modules/mappers/mod_rewrite.c
===================================================================
--- httpd-2.2.21/modules/mappers/mod_rewrite.c	(revision 1179633)
+++ httpd-2.2.21/modules/mappers/mod_rewrite.c	(working copy)
@@ -4266,6 +4266,13 @@
         return DECLINED;
     }
 
+    /* Check that the URI is valid. */
+    if (!r->uri || r->uri[0] != '/') {
+        ap_log_rerror(APLOG_MARK, APLOG_ERR, 0, r,
+                     "Invalid URI in request %s", r->the_request);
+        return HTTP_BAD_REQUEST;
+    }
+    
     /*
      *  add the SCRIPT_URL variable to the env. this is a bit complicated
      *  due to the fact that apache uses subrequests and internal redirects