Cisco 600 series routers running CBOS 2.0.1 through 2.4.2ap allows remote attackers to cause a denial of service via multiple connections to the router on the (1) HTTP or (2) telnet service, which causes the router to become unresponsive and stop forwarding packets.
https://exchange.xforce.ibmcloud.com/vulnerabilities/7026
https://exchange.xforce.ibmcloud.com/vulnerabilities/7025
http://www.cisco.com/warp/public/707/cisco-cbos-webserver-pub.shtml