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I have an Ubuntu 18 server which is being used as a VPN server ( V2RAY ) . My VPS provider ( OVH ) has sent me this abuse report :

2022.10.22 12:40:47 CEST 51.91.11.***:53258 8.8.8.8:443 TCP SYN 60 ATTACK:TCP_SYN
2022.10.22 12:40:47 CEST 51.91.11.***:43752 157.240.21.63:443 TCP SYN 60 ATTACK:TCP_SYN
2022.10.22 12:40:47 CEST 51.91.11.***:49242 179.60.192.52:443 TCP SYN 60 ATTACK:TCP_SYN
2022.10.22 12:40:47 CEST 51.91.11.***:49166 179.60.192.52:443 TCP SYN 60 ATTACK:TCP_SYN
2022.10.22 12:40:47 CEST 51.91.11.***:49004 179.60.192.52:443 TCP SYN 60 ATTACK:TCP_SYN

It seems to me that a client is using the VPN for attacks . How can I stop SYN packets from going out of my server ?

Mr Pro
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1 Answers1

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SYN packets are required for any TCP connections from your server.

You should have proper contract with your client, where you disallow service use for malicious purposes like SYN flood. Based on that contract, you would block the client from using your service.

If you want to have technical limitations, then you can set up rate limiting for SYN packets based on source IP address. However, those limits have to be carefully designed so that it does not disturb clients' normal service.

Tero Kilkanen
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