An OpenSSH daemon listens on TCP port 22. There is a hard-coded entry in the "/etc/shadow" file in the firmware image for the "root" user. However, in the default SSH configuration the "PermitRootLogin" is disabled, preventing the root user from logging in via SSH. This configuration can be bypassed/changed by an attacker through multiple paths though.
Exploitability
AV:NAC:HPR:NUI:NScope
S:UImpact
C:HI:HA:H8.1/CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:HOther