A distributed denial of service attack (DDoS) occurs when multiple systems flood the bandwidth or resources of a targeted system, usually one or more web servers. These systems are compromised by attackers using a variety of methods.

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Using an Ubuntu VPS as a firewall/router

I have a dedicated server running ubuntu 12.04 hosting several websites and other applications which require client IP's to be visible, however the main dedicated server does not have DDoS protection, ...
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1answer
65 views

How to AVOID getting caught in a DDOS meant for someone else (not prevent)?

So we have a load balancer and all that jazz set up with Rackspace. However, guess what, our clients' websites were down again today. It seems that Rackspace should have their load-balancer ...
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2answers
74 views

How do I understand my CPU usage on a DNS server?

I have read and understood Can you help me with my capacity planning?, but I'm not sure I understand what my next steps are in a DNS server scenario. I think my CPU loads are high or that I might be ...
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2answers
153 views

Setup alternative DNS entry while DNSimple is down for DDoS?

Have an app on Heroku with domains registered with DNSimple. DNSimple is undergoing DDoS for hours. (Sharing the naked heroku URLs with users is almost workable, but not an option as the OAuth ...
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1answer
47 views

How can I block traffic FROM Amazon Technologies Inc. (possible DDOS attack) [closed]

I've a small website (portfolio) and I usually notice traffic of about 10-20MB per day. But for few recent days I've noticed about 10-15GB (1000 times more) each day for 4 days now (and it continue ...
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0answers
30 views

Multiple pearl processess all hitting one IP address DDOS source hack? [duplicate]

I have been running at high CPU loads 45 45 45 ish for a while, updated cpanel / apache so far but tracing PID's that are running I find the following all with the same IP.. [code] select(8, [3], ...
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0answers
41 views

My VPS send an outbound attack

My VPS was sending an large outbound attack 10MB/s. It's normal max 300Kb/s I've tried searching around the internet, look for some /tmp folder, installed Linux Malware Detect, installed csf with ...
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22 views

Digital Ocean droplets get locked down because of outgoing DDOS attacts [duplicate]

Two of my droplets were locked down this week from my account for an apparent reason of outgoing DDOS attack. My first machine was allegedly compromised on Nov 18 2014 and my networking is brought ...
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37 views

How to redirect to an other link when excess request (limit_req) with Nginx

I have been trying to limit the requests coming from a single IP address successful with module limit_req in Nginx. But now I want to redirect to an other web-page for showing some messages.How could ...
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1answer
51 views

How to drop first udp packet from a source with iptables?

As a defense against distributed udp flood, I need to drop first udp packet from a source and accept other than first packet. Does iptables has capability of doing this? If yes, how?
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1answer
60 views

GRE Tunnel in CentOS

How to create a GRE Tunnel in CentOS pointing all connections to server A for the server B? I have a public server with DDoS protection and need to use this as a firewall to filter acess to the other ...
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2answers
35 views

What is the benefit of cloudfares or inkapsulas etc ddos protection [closed]

My Server get even more attacked via DDOS. And im thinking about buying a service like cloudfare or incapsule for preventing DDOS. But i dont understand one thing. When the attackers see that the ...
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1answer
68 views

Can I block inbound traffic from a certain ISP

The problem My server keeps getting DDoS attacks from IP's belonging to Ecatel in The Netherlands. I wrote them a month ago and still haven't heard anything, and keep blocking individual IP addresses ...
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0answers
432 views

Apache Server 2.4 on EC2 “caught SIGTERM shutting down ”

I'm using amazon linux on an m3.large instance on EC2. I had these logs before my apache server was shut down: [Sun Sep 28 18:54:31.679261 2014] [cgi:error] [pid 32422] [client 67.211.230.58:58937] ...
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0answers
34 views

Recommended values for DIPR configuration on a web-server

Microsoft has this great module for IIS server: The Dynamic IP Restrictions (DIPR) module for IIS 7.0 and above provides protection against denial of service and brute force attacks on web ...
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2answers
185 views

Block incoming traffic from unresolved IP address

How can I block all the incoming traffic from unresolved IP addresses? I am using CentOS with WHM/cPanel installed. I am getting huge junk traffic and 95% is from unresolved IP addresses and only 5% ...
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1answer
46 views

there is empty ips in netstat

I have installed ddos deflate on my sever (centos6.5 64bit) and in server mailbox I see that ddos deflate has been blacklisted empty Ip. and when I run this command on ssh I see: netstat -ntu | awk ...
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1answer
74 views

Unknown arg `--hashlimit-upto'

I'm trying to prevent loic attackes by using this command iptables -A INPUT -p tcp --dport 80 -m hashlimit --hashlimit-upto 50/min \ --hashlimit-burst 500 --hashlimit-mode srcip --hashlimit-name http ...
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1answer
74 views

Need help examining tcpdump file to block attack

I need some help, my game server has been under fire with DoS attacks for 2 days now. Bandwidth attacks are no problem since I host with OVH and they are filtered out but my game server ports are ...
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1answer
72 views

Lots of connections to loopback, could be slowing us down

I'm trying to debug a sudden increase in our load average. I looked at this page to see if we were being DDoS'ed but the standout IP address was the loopback address: $ netstat -ntu | awk '{print ...
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0answers
88 views

Is it DDOS attack?

For three successive days, now, I'm having four or five unique servers' queries being denied by my csf firewall, which are renamed in the following extract I got from my log as "www.example1.com", ...
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1answer
335 views

.htaccess rules to stop DDoS POST flooding

We're under a distributed denial of service attack from traffic that looks like this: 49.146.161.175 - - [11/Jul/2014:00:43:42 -0400] "POST / HTTP/1.1" 500 557 "-" "Mozilla/4.0 (compatible; MSIE 6.0; ...
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2answers
142 views

blocking udp attack ip with iptables

I was trying to block an ip of ( network stresser tool - a ddos websites selling ddos bots by seconds online ) the first one i was trying to block with iptables : iptables -A INPUT -d 173.193.26.73 ...
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2answers
156 views

Does “TARPIT” have any known vulnerabilities or downsides?

TARPIT can be used to waste an attacker's resources, thus slowing down his attacks and lowering his ability to attack other hosts... looks like a good idea. It is provided as a Netfilter addon and ...
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2answers
122 views

Does CloudFlare make a site a greater potential DDOS target?

CloudFlare has gotten a lot of press recently as protecting businesses from DDOS attacks. But from looking at their twitter feed, it looks like they are targeted every day, and large segments of their ...
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3answers
477 views

My webserver is getting flooded with invalid requests

My webserver (nginx) keeps getting requests like this: 23.244.104.206 - - [15/Jun/2014:21:21:47 -0400] "GET ...
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0answers
118 views

How do you protect your <appid>.appspot.com domain from DDOS attack?

If I want to use CloudFlare to help protect my GAE app via it's custom domain, I still am vulnerable to attacks directly on the .appspot.com domain. How do I mitigate that? I could force redirect ...
0
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1answer
290 views

iptables to allow input and output traffic to and from web server only

I have an Elastic Search server which seems to have been exploited (it's being used for a DDoS attack having had NO firewall for about a month). As a temporary measure while I create a new one I was ...
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2answers
63 views

How to find the count of Apache workers' at a given point for shared IPs?

One can find the number of Apache workers an IP address is consuming at an instantaneous point in time by executing: netstat -pantu | grep :80 |sort | uniq -c |grep <IP_HERE, eg: 192.168> | wc ...
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2answers
154 views

Is it possible to prevent DDoS attacks? [closed]

I recently read that certain industries—including the one I work in—are more likely than others to be targeted by a DDoS attack. Can you give me some tips on how to prevent DDoS attacks?
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1answer
435 views

SynFlood attack, spoofed IPs, syncookies mitigation

Due to a recent increase in SynFlood attacks on my company's systems i've been testing by Syn flooding the hosts myself to see how easy they are to disrupt, and the answer is 'quite easy'. By using a ...
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0answers
275 views

Curl Sourced DDoS: How to detect it & how to stop?

Okay, an Ubuntu server I manage fell victim to a DDoS attack today. Usually this is unpleasant but not that big a deal. A few high server load moments & then it passes. Today was clearly ...
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0answers
538 views

High outbound network traffic on Tomcat under process nodeJR

We are investigating high outbound traffic on Tomcat servers hosted on AWS instances. The specific question I have is what the process nodeJR is - and how it could get installed under Tomcat? The ...
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0answers
46 views

Multiple DDOS protection interfaces merging on one TS server

The problem I have is I have 3 DDOS protection interfaces from a multi homed DDOS protection solution and teamspeak is refusing to return packets via the correct interface (aka the one that sent it ...
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0answers
247 views

Apache2 php-cgi processes, how to limit them?

I have a 32gig ram dedicated server running on Ubuntu 12.04 with ISPConfig / Apache configuration. The thing is, anyone can take the site down simply by holding down F5 button for 20 seconds causing ...
2
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1answer
357 views

Outbound DDOS Attacks Being Run from Our Server

We run a mail server (postfix/dovecot/centos 6.4). The hardware is based on a supermicro chasis with IPMI features. It also runs a web interface for accesisng mails(Apache web server ) Recently our ...
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1answer
736 views

Apache logs flooded with connections - “(via ggpht.com GoogleImageProxy)”

My server was running on 100% CPU and looking at the Apache logs I saw hundreds of thousands of connections that looked like this: 10.190.45.31 - - [13/Mar/2014:15:29:02 +0000] "GET SOMETHING ...
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1answer
315 views

blocking all countries except 4 at vlan level, will cisco asa 5505 hold?

First our server hold an application that only serve 4 countries. We had a repeated ddos from bonnet so would like to block all traffic except for the 4 countries that the application serve. the idea ...
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1answer
51 views

How to tell if the server was down because of DDoS of another reason?

my server was down for a couple of hours during the night. i see in the cpu load monitoring in the amazon AWS console that it was 100% load. also, the network in jumped (but no that dramatically) so ...
4
votes
2answers
96 views

Will MX records with a longer TTL help mitigate effects of DoS attack?

We have our email hosted at Google Apps, and have our DNS servers for the domain setup at Namecheap. About a month ago our website went down (not a big deal, since it's most just a contact info ...
1
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1answer
83 views

Apache MySQL Server Crashing - Large number of connections from localhost

I'm running a 2GB Centos 5.9 server with the standard LAMP setup. I'm running a wordpress website so it's nothing to demanding performance wise. However the MySQL server seems to keep crashing as I ...
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2answers
1k views

Apache - How to limit Content-Type header length to avoid CVE-2014-0050?

On Thursday a DoS problem with Tomcat was announced in a Tomcat mailing list ("[SECURITY] CVE-2014-0050 Apache Commons FileUpload and Apache Tomcat DoS"). An attacker seems to be able to cause an ...
4
votes
5answers
2k views

How can I defend against a DRDoS exploiting NTP server on an ESXi host?

Recently, we had some problems with one of our ESXi servers, caused by the NTP Server DRDoS Amplification Attack using ntpdc. How do I configure the NTP server on ESXi to not be exposed to this DDoS ...
12
votes
1answer
4k views

What is an open DNS resolver, and how can I protect my server from being misused by hackers?

I don't have the strongest background in computer security, but yesterday one of my company servers was shut down by our host. It's a server assigned a public IP where I host several web-service ...
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1answer
127 views

How to read sFlow?

We currently have a very large outbound DDOS Attack coming from one of our machines which is on a Brocade switch and monitored by PRTG. I am looking at the sFlow v5 8 sensor and see Top Talkers and ...
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0answers
224 views

My Bitnami Tomcat Stack (on EC2 AWS) is generating DoS attack

I have a very small java web app that is deployed on a Bitnami Tomcat Stack on AWS. We are using this app in the company with only 5-10 user base daily, and generating only below 100MB of traffic per ...
0
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2answers
2k views

mod_security configuration issue: Error parsing actions: Unknown action: ver

I am trying to install / configure mod-sec using this tutorial, which uses the OWASP ModSecurity Core Rule Set. However when I go to restart apache, I get the following error: Syntax error on line 53 ...
3
votes
3answers
600 views

Can't stop DDOS [duplicate]

I need a little help dealing with ddos. I'm experiencing 1gb ddos attack on my server and I don't know how to stop it. (1gbs is the maximum speed of the server.) I've the following iptables rules: ...
0
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1answer
711 views

How to prevent mod_evasive false positives on partial downloads of large files

I am getting a lot of false positives notices sent by mod_evasive installed on my apache servers. They always happen on large PDF file downloads. When clients download PDFs from my site, they use many ...
5
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3answers
2k views

DDOS using ntp server

I've heard about new kind of DDOS where ntp is used for reflection . My questions are really simple : Can you please give details on how they work and clarify? Since ntp is ran over UDP, I suppose ...