OpenSSH UseLogin Vulnerability

OpenSSH is a free derivative of ssh1, a secure remote login tool. An option can be set to use the login program (the option is 'UseLogin') - this is set to 'no' by default in most distributions. When UseLogin is turned on, sshd doesn't set the uid of the person logging in to what it should be, it remains running as root. This can be exploited if a command is specified (to be executed) on the target host running sshd via the ssh client. Since instead of logging in, a command is being run, "login" is not used and therefore cannot set the correct userid. Any command executed remotely via ssh where "UseLogin" is on will execute as root, leading to a trivial compromise.


 

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