Firefox 1.5.0.7 and 2.0 and Seamonkey 1.1b allows remote attackers to cause a denial of service (crash) by creating a range object using createRange calling selectNode on a DocType node (DOCUMENT_TYPE_NODE) then calling createContextualFragment on the range which triggers a null dereference. NOTE: the original Bugtraq post mentioned that code execution was possible but followup analysis has shown that it is only a null dereference.