The most serious of the findings is the authentication bypass CVE-2024-51978. A remote unauthenticated attacker can leak the target device’s serial number through one of several means, and in turn generate the target device’s default administrator password. This is due to the discovery of the default password generation procedure used by Brother devices. This procedure transforms a serial number into a default password. Affected devices have their default password set, based on each device’s unique serial number, during the manufacturing process. Brother has indicated that this vulnerability cannot be fully remediated in firmware, and has required a change to the manufacturing process of all affected models.

So the fix for this “can’t be fixed” issue is to change the default password yourself, which you should be doing anyway.