Attack on user agent?

[SPB]

Hi, can you tell me what is the user agent they try to authentificate?


IP (hacker ip) has been blacklisted on PBX (my external pbx url).
Affected Module: SIP Server/Call Manager
User agent: <N/A>

The IP (hacker ip) has been blacklisted for 86400 seconds. (Expires at: 2020/06/03 03:37:53).
Reason: Too many failed authentications! This IP Address has made numerous attempts to authenticate with 3CX with invalid authentication details. Therefore a blacklist rule has been created denying this IP to continue sending requests.

 

[StefanW]

The User-Agent is not mandatory but when specified cannot be blank.
In this case, the user agent string in the SIP Header is absent. Hense N/A.