HG8145V5 TELNET/WAP/SHELL ACCESS (COMMON VALID COMMANDS)

Hello everyone,
I realized that I could access the router by telnet using the command and credentials:

$telnet 192.168.100.1 23
Username: root
Password:  adminHW

Once connected at the WAP> command line I could change the access type using the command su, and it was changed to WAP_SU>, then I typed shell and could take a shell access as root:

BusyBox v1.26.2 () built-in shell (ash)
Enter 'help' for a list of built-in commands.

profile close core dump
WAP(Dopra Linux) #

So, I have 3 questions related with this:

1. Can I change the standard password adminHW to another one; in a positive case, what is the command sequence that I have to use?

2. Are there any HUAWEI command list, with the common commands used in this kind of access?

3. And finally  I want to know if it is a kind of backdoor used to upgrade the router software/firmware... This is the most important question that I have, since it maybe related with my network security; becouse now I'm thinking that someone with bad intentions could be accessing to my network...