Update to 1.43.3.10861+ ASAP before your server gets taken over. Full server compromise exploit is now public:
Folks are starting to get hit by it:
https://www.reddit.com/r/PleX/s/LilsCZahFh
https://www.reddit.com/r/PlexMedia/s/gLWcTOmEAA
https://www.reddit.com/r/PlexMedia/s/MxIuE3DDKd
The original announcement about it:
And old vulnerability. This is why auto-update is a good thing to do.