Vulnerability Discussion

Tmux is a terminal multiplexer that enables a number of terminals to be created, accessed, and controlled from a single screen. Red Hat endorses tmux as the recommended session controlling package.

Satisfies: SRG-OS-000031-GPOS-00012, SRG-OS-000028-GPOS-00009

Check

Verify RHEL 9 shell initialization file is configured to start each shell with the tmux terminal multiplexer.

Determine the location of the tmux script with the following command:

$ sudo grep tmux /etc/bashrc /etc/profile.d/*

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

Review the tmux script by using the following example:

$ 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 the shell file is not configured as the example above, is commented out, or is missing, this is a finding.

Determine if tmux is currently running with the following command:

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

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

Fix

Configure RHEL 9 to initialize the tmux terminal multiplexer as each shell is called by adding the following to file "/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