iPlanet Web Server Enterprise Edition 4.1 and earlier allows remote attackers to retrieve sensitive data from memory allocation pools, or cause a denial of service, via a URL-encoded Host: header in the HTTP request, which reveals memory in the Location: header that is returned by the server.
http://www.kb.cert.org/vuls/id/276767
http://www.iplanet.com/products/iplanet_web_enterprise/iwsalert4.16.html
http://www.atstake.com/research/advisories/2001/a041601-1.txt