SYN Flood .. No Way To Stop It ?
Oct 30, 2007
One of the servers have 1 account on, but seems like its extremely attacked. I cannot SSH and many packet loss. so I asked softlayer and they access it and said its a SYN Flood as from the /var/log/messages (I cannot see it as the server is not accessable) they put the main public ip under Cisco guard but still didn't help. when I asked for any solution, unfortunaly I were told there isn't and have to wait the attackers to stop as it comes from MANY addresses that iptables even won't help.
Isn't there any solution (software-hardware) to stop that ?
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May 11, 2009
I've been getting a syn flood for the last week or so.
I've pretty much tried everything I could online but have been unsuccessful in stopping them.
I talked to the data center techs and they basically can't put a stop to it either.
Here's a very small portion of my netstat
tcp 0 0 xxx.xxx.xxx.xxx:80 86.50.121.144:8540 SYN_RECV -
tcp 0 0 xxx.xxx.xxx.xxx:80 41.100.16.152:7824 SYN_RECV -
tcp 0 0 xxx.xxx.xxx.xxx:80 52.53.22.7:3146 SYN_RECV -
tcp 0 0 xxx.xxx.xxx.xxx:80 77.217.49.124:1659 SYN_RECV -
tcp 0 0 xxx.xxx.xxx.xxx:80 75.162.93.151:3230 SYN_RECV -
tcp 0 0 xxx.xxx.xxx.xxx:80 113.85.63.249:1656 SYN_RECV -
tcp 0 0 xxx.xxx.xxx.xxx:80 15.253.35.29:8849 SYN_RECV -
tcp 0 0 xxx.xxx.xxx.xxx:80 24.56.59.180:6911 SYN_RECV -
tcp 0 0 xxx.xxx.xxx.xxx:80 33.185.99.83:1917 SYN_RECV -
tcp 0 0 xxx.xxx.xxx.xxx:80 103.5.8.249:4782 SYN_RECV -
root@xxx [/]# netstat -nap |grep SYN |wc -l
2008
The IP's change often and it's not possible to narrow it down.
So far the things I have done;
syn cookies enabled
reduced time out
echo "1" > /proc/sys/net/ipv4/netfilter/ip_conntrack_tcp_timeout_syn_recv
increased
echo "150000" > /proc/sys/net/ipv4/ip_conntrack_max
installed apf but it slowed down the server to a crawl which made my clients really unhappy so had to remove it.
The bandwidth is constantly staying at 30Mbps with slight bumps here and there but every day around 7pm it drops completely to normal levels and the flood stops. It starts back up around 7 in the morning.
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Jul 28, 2009
We are currently experiencing an SYN Flood attack on our primary production server and are looking for some help in resolving the issue.
Running:
Novell SUSE Linux Enterprise Server 10.2-64
SuperMicro X7DBR-E Intel Xeon QuadCore DualProc SATA [2Proc]
Processor Intel Xeon-Clovertown 5320L-QuadCore [1.86GHz]
8GB Memory
@ Softlayer DC in Texas.
Need help within the next hour or two. Please ask any necessary follow up questions and how you might go about resolving the issue (i.e. SYN Cookies, etc.)
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May 3, 2009
someone decided to attack my webserver and I can't figure out how to block it.
tcp 0 0 localhost:80 207.44.129.88:2138 SYN_RECV
tcp 0 0 localhost:80 207.44.129.88:2243 SYN_RECV
tcp 0 0 localhost:80 213.66.121.211:63372 SYN_RECV
It's literally thousands of those requests overloading apache. The server is fine, the load average is like .8. But none of the website are loading.
We're hosting with ThePlanet, and they're doing a great job at blocking a huge portion of the attack. But we're still getting hit pretty hard. I've got APF installed, and 3 or 4 anti-dos scripts.
Every once in a while a page will load for the websites, I think we've got just under 50 legit connections.
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Jun 11, 2008
How can I best work with a syn flood? I've tried the apf, deflate-ddos etc.... and don't work. Even tried litespeed etc but doesn't work against a 90mbps attack.
If I get a few servers, how would I have it setup to best defend?
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Jul 25, 2008
one of my server were hit by massive ddos syn atack. target was port 80-apache
i am running centos 5 in xen vps iptables were strong with syn filtering and limit
but...what can do?
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Mar 8, 2008
I don't know it anymore. Tried everything. I can not reach my server properly. A lot of time time out.
netstat -anp |grep 'tcp|udp' | awk '{print $5}' | cut -d: -f1 | sort | uniq -c | sort -n
1 127.0.0.1
1 38.99.44.101
1 64.131.90.38
1 78.176.158.75
1 78.179.73.135
1 88.229.70.143
1 88.242.97.204
1 88.247.87.58
1 92.112.211.223
3 78.176.175.136
3 88.229.40.142
3 88.231.180.181
4 78.183.227.146
18 0.0.0.0
348
348 connections from an empty IP? i have tried syn cookies, let the firewall block all ports without results.
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May 28, 2008
Can anyone share tips how to prevent DNS flood on a cPanel and Directadmin server platform on Centos?
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May 29, 2008
Does keepalive off help in syn flood?
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May 4, 2008
My server run after 10h sevices ftp is down (network error: connection timed out). may be flood ftp.
how to Detect flood ftp.
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Apr 4, 2008
We got hit with a huge bandwidth bill for last month. It was 4X our usual bill. The ISP said that we were the victim of UDP flood attacks from an outside server. We have a sonicwall router and the firewall seems to be blocking the port that the ISP claims the attacks can from. Is it possible that the attacks would still count towards our bandwidth usage even if the connection is refused by our firewall? Our ISP uses 95th percentile billing.
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Jun 25, 2008
one of my costumers server is getting ddos attacks. I solved syn and get attacks with litespeed web server but I have another problem. They started to do udp flood. I m losing connection to my server. I bought new server with 1 gbit port for solving it.
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Oct 27, 2008
flood in FTP and brute force
all day i receved msgs of BFD someone trying acess server, how to stop it, exemple:
Executed ban command:
/etc/apf/apf -d 221.186.164.233 {bfd.pure-ftpd}
The following are event logs from 221.186.164.233 on service pure-ftpd (all time stamps are GMT -0500):
Oct 25 13:52:37 svr1 pure-ftpd: (?@221.186.164.233) [INFO] New connection from 221.186.164.233
Oct 25 13:52:37 svr1 pure-ftpd: (?@221.186.164.233) [INFO] New connection from 221.186.164.233
Oct 25 13:52:38 svr1 pure-ftpd: (?@221.186.164.233) [WARNING] Authentication failed for user [router] ....
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Jul 26, 2009
I use Outpost Firewall to view active connections to my server. If I don't restart the httpd service on a regular basis my server will grind to a halt from being flooded by robots.
I currently have the service set up to restart at Midnight and Noon every day. Sometimes that's enough, lately it's not. For example, I checked an hour ago and I had 385 connections to httpd. At least 50% of the connections were robots - tons of the same IP addresses and they're just crawling the site.
Almost all of the connections show up as less than 1kb bytes received and 0 bytes sent per connection.
I already have a good 20 connections by these robots and the connection time shows as 11 minutes... I just browsed to a web gallery page on my site figuring that'd be mildly "intensive" on connections with all the thumbnails and my connections aren't lasting more than one minute.
So, what's with all these connections that are lasting 10+ minutes? I've even got one connection that has an Uptime of 30 minutes, bytes sent 65811, bytes received 180. It seems like something with these robots doesn't terminate correctly...
what to do so these connections quit jamming my server up? It's like a very very slow DOS...
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Aug 1, 2007
When I check on port 80 connections, I get a list of few IPs with more than 100 connections.
I need to know which website / specific file being downloaded / URL is the IP accessing to? How can I do that?
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Jan 11, 2007
my server under attack with syn flood and i attach the active connection during attack
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Jun 20, 2007
some of my friend website is under attack by Ddos ; FLOOD ; and other way to down his site !
how can we save him from these attacks?
else the firewall!
1- is there any program or script to prevent these attacks!
2- is there any rules or script's for Firewall to prevent it!
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Jun 5, 2015
I serve large professional documents, and sometimes links to them end up on social media. No big deal, but I think people clicking on them from tose social media sites don't have a clue. They think they're being directed to small page, when in fact they are downloading megabytes of pdf -- myfile.pdf. So what I've started to do is to redirect requests from social media to an archive page, where they can see specifically what document they are trying to get, and recognize its size before they ask for it. No problem, right? I just do
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May 1, 2009
my DNS stop resolving, once a day i need to restart the service in cpanel/whm , what can be done to prevent that ?
its a fresh vps only cpanel is there and 2 domains with no pages just a simple under costruction index page . in CSF i have a Your Score: 106/112 in security , it firewalled and hardened
right now is using 299 of ram out of 512 burstable to 768
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Jun 30, 2008
I was wondering if anyone has any methods to stop spammers? Currently i am keeping watch on the mail queue and making sure nothing unsual. I have in WHM configuration setup to not allow more 200 mail messages per account per hour but for some reason it will hit thousands. WHMCS does seem to suspend them automatically or maybe its because of WHM BUT only when its too late.
Any thoughts or suggestions?
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Jun 2, 2009
Have a persistent spammer who kept emailing my clients, even non existent domain accounts and getting the bounced emails to be send to a particular yahoo address. I tried to block in all ways but can't seem to stop him. His spams are from all over the world. Any suggestions?
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Nov 5, 2009
How to stops the scripts like c99 shell from installing into the server?
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Jul 1, 2009
how to stop gunzip -c?
By mistake instead of using gunzip file name on my friend's vps, I had used gunzip -c filename
and its taking hell a lot of time to unzip it, I have no clue on how to stop this and I am scared if I close ssh client, it might be still adding load to the server ..
I am unzipping an 4.5mb file, which on un-compression must be around 14.5mb ..
for the past 10 mins its still unzipping and not sure how long it will go on.. unless I stop it..
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Feb 6, 2009
a site i manage for a client is being hacked every couple of days, its not the actual site but the hosts server thats getting attacked, all sites on that server, well actually all thier servers.
They have made no attempt to sort this problem, i report it they look at the site and say "site loads fine for us" which it does.
All index files are having a base64 encode line written after the <body> tag, this adds hundreds of spam links which are hidden with display:none; they also add .html to application types in htaccess for php to run in these files too.
Problem is, i am moving the site to another host but cannot change the nameservers to the new host's untill the client returns from a holiday, so i must keep the site up on the insecure host for now.
I am removing the spam code almost daily, is there anyway i can stop this attack happening for the time being, the host does nothing.
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Apr 17, 2009
I have a server that is sending spam, but I can not know who sent because the server not has installed suphp.
There is another option to see who sends spam?
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Jul 19, 2009
Is there a way to stop hotlinking? I have a client who has a blog. They have post pics of tattoos. Now there are at least 50 tattoo forums, blogs and other sites hotling to the pics. Now his bandwidth usage has skyrocketed. So enable hotlink protection in his cPanel. Just did a redirect to my main hosting site with a nice please stop hotlink image. Now I see all this in my logs. So I then made a 150 x 9000 clear BG gf with the text at the top please stop hotlinking.
My questions is there any way to stop it. If not should I just make a 1x1 clear gif to redirect to? Also is there a way to not have this traffic show in my log files?
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Dec 25, 2008
I want to stop emailing myself
I have received quite a few emails from senders claiming to be the recipients [in this case one of my email accounts]. I did not send these emails. This is happening with almost every email account I have setup on one of my domains.
I know this is probably an easy fix-- I am simply unsure of what it is.
I noted that someone else recently posted a similar question-- with only one response. I wanted to see if another post my garner another response.
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Nov 14, 2008
I would like to ask about the best system or software code used to stop bots and offline down loaders from entering website.
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May 4, 2008
to stop iptables cause when any user make refresh he is take banned from server
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Jun 14, 2008
I already enabled awstat in whm features manager.
And it was working till 3 jan 2008!
But statistic doesn't update now!
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