The PPTP ALG implementation in Cisco IOS XE 3.9 before 3.9.2S on 1000 ASR devices allows remote attackers to cause a denial of service (device reload) by sending many PPTP packets over NAT, aka Bug ID CSCuh19936.
http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20131030-asr1000