The Omron FINS protocol has an authenticated feature to prevent access to memory regions. Authentication is susceptible to bruteforce attack, which may allow an adversary to gain access to protected memory. This access can allow overwrite of values including programmed logic.
Omron CJ1M unit v4.0 and prior has improper access controls on the memory region where the UM password is stored. If an adversary issues a PROGRAM AREA WRITE command to a specific memory region, they could overwrite the password. This may lead to disabling UM protections or setting a non-ASCII password (non-keyboard characters) and preventing an engineer from viewing or modifying the user program.