HMAC authentication Failed : Attack

sofo

Team,

I have 2 Openvpn servers . But recently I am experiencing HMAC authentication Failed Attack.

I Use user pass authentication , No client cert required. Normally In 24 hours my serverlog size goes upto 400 -500 Kb ( verb 1)

But for last few days I see within an hour serverlog size becomes 30 -40 MB and server not responding through It is not crashed.

90% of lines in serverlog only contains [ Authenticate/Decrypt packet error: packet HMAC authentication failed ].

I given valid server certificate to my client and all were using it well for last 3 months ..But suddenly it started happening.
Can anybody pls tell what actually it is going and how should I proceed to fix it.

Thank you

sofo

Thanks debbie10t. I have done it and Its okay now.

Can you please check following link . I have spent few weeks now without any luck. Any pointer direction will be very helpful.
I heard TUN/TAP Driver stall / Hang ....I don't know if it is my case. I can confirm it is not related to any Dos attack.

I have 3 openvpn instances in same machine (2 UDP +1 TCP ) using 3 different TUN devices.

TCP is always OK...But Sometime 1 UDP becomes non responsive then becomes stable automatically. And again another UDP becomes non responsive then again corrected automatically after 1-2 hours. It happens 1-2 times daily and some time 3-4 times in a week.

How should I debug this case. If I see UDP packet coming from client machine using TCPDUMP and openvpn not accepting it . Neither any thing written in log (verb 6) . I have setup a Custom UDP server binding to same IP ..It is always OK. During this time Openvpn still running consuming 0.0% CPU.

https://forums.openvpn.net/topic13990.html

Many Thanks

[deleted]

What country are your users connecting from?