The WD My Book Live series NAS has two models, a single-disk one called just My Book Live where the disk is not user-replaceable, and a dual-disk one called My Book Live Duo where the two disks can be replaced tool-free. AnandTech had a pretty thorough review of the single-disk one
https://www.anandtech.com/show/4952/wd-my-book-live-network-....
I had the MBL Duo. It ran on an 800MHz Applied Micro APM821XX PowerPC processor with 256MB RAM. The stock firmware was a customized version of Debian. I couldn't remember exactly which version of Debian but it's definitely older than Debian 9. Maybe 6 or 7? Anyway, you can enable SSH access via web UI and directly login to the device and see everything running there.
IIRC WD used OpenVPN to establish a connection to their servers to allow remote access to these devices behind NAT and firewalls. I had always been wondering what if their servers were hacked and then hackers could theoretically access the NAS via that VPN connection and by extension my LAN behind firewalls so I disabled the remote access feature.
A couple of years back I finally got tired of the ancient Debian, and since WD had already deprecated the device without further updates/patches, I was looking for alternatives. There were people on WD forums trying to compile and install newer versions of Debian. But since the device does not have video out or console port, it was very easy to mess up and got bricked.
Eventually I found OpenWRT (yes, the linux-based router OS) had official support for both MBL models (https://openwrt.org/toh/western_digital/mybooklive) and the installation seems pretty safe (especially for the Duo with replaceable disks). So I went with OpenWRT and never looked back.
My MBL Duo now sits at my parents-in-law's place running OpenWRT. I had setup WireGuard to connect it to my LAN in another city and used it as a remote backup destination in case of either place catching fire or whatever other disasters.
And now I feel pretty lucky for my decision to ditch the original firmware. Good riddance!