OpenSSH on FreeBSD 5.3 and 5.4, when used with OpenPAM, does not properly handle when a forked child process terminates during PAM authentication, which allows remote attackers to cause a denial of service (client connection refusal) by connecting multiple times to the SSH server, waiting for the password prompt, then disconnecting.
https://exchange.xforce.ibmcloud.com/vulnerabilities/25116
http://www.vupen.com/english/advisories/2006/0805
http://www.securityfocus.com/bid/16892
http://securitytracker.com/id?1015706