The checkHTTPpassword function in http.c in ntop 3.3.10 and earlier allows remote attackers to cause a denial of service (NULL pointer dereference and daemon crash) via an Authorization HTTP header that lacks a : (colon) character in the base64-decoded string.
http://www.vupen.com/english/advisories/2009/2317
http://www.securityfocus.com/archive/1/505876/100/0/threaded
http://www.securityfocus.com/archive/1/505862/100/0/threaded
http://www.mandriva.com/security/advisories?name=MDVSA-2010:181