Home » Kerio User Forums » Kerio Control » DDOS (maybe) over port 80
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bigmountain

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Has anyone been experiencing a DDOS attack over port 80 in the past few days? I am seeing several IPs and in one case an entire class C block of addresses attempt to connect to most of the IPs on our network via port 80 TCP. I do not see any activity from these IP when I go to the individual host, so I have to assume that Control is dropping the connections. However, sometimes I see the connections dropping on their own and other times they do not seem to drop and I have to manually block the IP and/or IP range. When these attacks are happening, http service freezes up on most of the hosts behind the firewall and at times, may disrupt standard smtp over port 25. It does not affect https, imap(s), dns, etc. just http and sometimes smtp. Even stranger, when these attacks happen, they are not connecting via smtp at all. So, I do not know why smtp get blocked for some hosts when the http attack occurs. Last, I do have connection limits set near the Kerio defaults and it does not seem that the connection limits are being met as they are not logged in the warning log and I am not receiving alerts indicating this. Has anyone encountered this? I do have a ticket in with GFI with all of the details, but am wondering if maybe there is something wrong with the latest antivirus or intrusion prevention update that introduced a bug that is preventing Control from properly handling these http requests?

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Columbia

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I also experience the same DDos stacks over port 80. Only manual block works. But this is not normal. Is it possible to get any comments from GFI about this problem ? May be it is possible to block inbound 80 port?
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bigmountain

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It is definitely not normal. Control has always properly dealt with these attacks for us. Fortunately, either the attacks have slowed down or Control has received updated intrusion prevention updates that maybe addressed these better. I can't explain it and I am still waiting to hear back from GFI. The type of attack appears to be SYN Flood, which is pretty common. According to my debug log (I have dropped packets checked), it seems to be dropping the connections of these unanswered SYN ACK responses at a faster pace, preventing the flood.

As for blocking port 80, that is easy, but we use port 80 on most of our machines.

Once I hear back from GFI, I will post an update.

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Columbia

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Thank a lot for any feedback.
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generator

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Same by me. Last 3 days massive DDoS attacks. We use Reverse Proxy. Connection limits doesn't help.
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Columbia

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Does GFI support come here on forum to publish any comments? The last official comment from GFI was in the summer. Is the forum dead?
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bigmountain

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I think I may have figured out the problem. Try unchecking the http scanning in the antivirus settings. I think there is a bug with it. Once I did that, Control properly deals with the SYN floods. I let GFI support know this, so I we are testing my theory now.

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Columbia

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I don't have a license for Antivirus. So this advice doesn't work for me.
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