This indicates an attack attempt to exploit a Command Injection Vulnerability in Yealink Device Management Platform.
The vulnerability is due to insufficient sanitizing of user supplied inputs in the application. An unauthenticated remote attacker may be able to exploit this to execute arbitrary commands with root privileges.
Yealink DM version 18.104.22.168 and prior
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor.