dubbo version 2.7.13，Telnet调用提示ls disabled for security reasons, please enable support by listing the commands through 'telnet'

telnet localhost 20881
```
dubbo>ls
Command: ls disabled for security reasons, please enable support by listing the commands through 'telnet'
```
这个是什么原因呀

Start with the Dubbo 2.7.13 Telnet command entry point and the security configuration or documentation referenced by the reported `ls` response. Determine whether disabling `ls` is expected, and identify the documented configuration or behavior that explains it; done means the issue has a clear, reproducible explanation.

Written by the indexing model from the issue text.