Vulnerability Discussion

Tmux is a terminal multiplexer that enables a number of terminals to be created, accessed, and controlled from a single screen.

Satisfies: SRG-OS-000028-GPOS-00009, SRG-OS-000030-GPOS-00011

Check

Verify the operating system shell initialization file is configured to start each shell with the tmux terminal multiplexer with the following commands:

Determine if tmux is currently running:

$ sudo ps all | grep tmux | grep -v grep

If the command does not produce output, this is a finding.

Determine the location of the tmux script:

$ sudo grep tmux /etc/profile.d/*
/etc/profile.d/tmux.sh: case "$name" in (sshd|login) tmux ;; esac

Review the tmux script by using the following example:
$ sudo cat /etc/profile.d/tmux.sh

if [ "$PS1" ]; then
parent=$(ps -o ppid= -p $$)
name=$(ps -o comm= -p $parent)
case "$name" in (sshd|login) tmux ;; esac
fi

If "tmux" is not configured as the example above, is commented out or missing, this is a finding.

Fix

Configure the operating system to initialize the tmux terminal multiplexer as each shell is called by adding the following lines to a custom.sh shell script in the /etc/profile.d/ directory:

if [ "$PS1" ]; then
parent=$(ps -o ppid= -p $$)
name=$(ps -o comm= -p $parent)
case "$name" in (sshd|login) tmux ;; esac
fi

This setting will take effect at next logon.