SSH Secure Shell for Servers and SSH Secure Shell for Workstations 2.0.13 through 3.2.1, when running without a PTY, does not call setsid to remove the child process from the process group of the parent process, which allows attackers to gain certain privileges.
https://exchange.xforce.ibmcloud.com/vulnerabilities/10710
http://www.ssh.com/company/newsroom/article/286/