fwknop before 2.0.3 does not properly validate IP addresses, which allows remote authenticated users to cause a denial of service (server crash) via a long IP address.
https://exchange.xforce.ibmcloud.com/vulnerabilities/79568
http://www.openwall.com/lists/oss-security/2012/09/20/4
http://www.openwall.com/lists/oss-security/2012/09/20/2
http://www.openwall.com/lists/oss-security/2012/09/19/2
http://www.cipherdyne.org/blog/2012/09/software-release-fwknop-2.0.3.html