Memory leak in the Data-link switching (aka DLSw) feature in Cisco IOS 12.1 through 12.4 and 15.0 through 15.1, and IOS XE 3.1.xS before 3.1.3S and 3.2.xS before 3.2.1S, when implemented over Fast Sequence Transport (FST), allows remote attackers to cause a denial of service (memory consumption and device reload or hang) via a crafted IP protocol 91 packet, aka Bug ID CSCth69364.