Cisco IOS 12.2, 12.3, 12.4, 15.0, and 15.1, when the data-link switching (DLSw) feature is configured, allows remote attackers to cause a denial of service (device crash) by sending a sequence of malformed packets and leveraging a "narrow timing window," aka Bug ID CSCtf74999, a different vulnerability than CVE-2007-0199, CVE-2008-1152, and CVE-2009-0629.