Multiple TCP implementations with Protection Against Wrapped Sequence Numbers (PAWS) with the timestamps option enabled allow remote attackers to cause a denial of service (connection loss) via a spoofed packet with a large timer value, which causes the host to discard later packets because they appear to be too old.
https://exchange.xforce.ibmcloud.com/vulnerabilities/20635
http://www.kb.cert.org/vuls/id/637934
http://www.cisco.com/warp/public/707/cisco-sn-20050518-tcpts.shtml
http://support.avaya.com/elmodocs2/security/ASA-2006-032.htm
http://secunia.com/advisories/18662
http://secunia.com/advisories/18222