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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Protection against scrapping with nginx

This morning we had a crawler going nuts on our server hitting our site almost 100 times per second. We'd like to add a protection for this. I guess I'' have to use HttpLimitReqModule but I don't ...
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1answer
165 views

Buffer-stuffing denial-of-service attack

I started seeing this odd sort of effect that resembles denial-of-service attack against a Linux server. The effect is that the network becomes at least partially unusable very much the same as what ...
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1answer
237 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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91 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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1answer
67 views

How to setup Microsoft DNS so it does not contribute to DNS amplification attacks

I am using a Microsoft DNS server to host both our internal and external DNS. This means that recursive lookups needs to be turned on, or internal users will not be able to perform DNS queries. ...
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1answer
104 views

Bingbot spoof localhost ip

So here is a fun one. I'm getting bingbot requests at a certain time everyday that kill the server. Here is the request: 127.0.0.1 - - [14/Sep/2013:08:18:49 -0500] "GET / HTTP/1.1" 200 82810 "-" ...
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1answer
332 views

Mitigate DDoS attack by Null-routing my server's IP?

My services were attacked by what appears to be a botnet of quite a large number of computers. Since all my servers have additional IPs, and my hosting provider lets me null-route my IP addresses to ...
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31 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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27 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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104 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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210 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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1answer
411 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 ...
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46 views

Is there a service I can redirect/report DDoS clients to?

Currently experiencing a very mild DDoS attack. Just a brute force login attack. This caused a spike in PHP/MySQL usage so I've just blocked logins except from my IP address. I'm not too worried about ...
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1answer
227 views

How to interpret this jnettop output?

Looks like I'm currently under a DOS attack or something like that, I've been monitoring the traffic on the server using jnettop, this is a of what I see during normal conditions: ...
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1answer
146 views

Automation of blocking IP address

I have an Ubuntu 12.04 machine running Apache2 which hosts about 10 wordpress websites. Recently I have been subjected to attacks from clients which seem to be sending POST requests to a wordpress ...
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1answer
40 views

My site is inaccessible from different locations on-and-off. What's happening?

On-and-off for the last few days, my sites (www.)aderet.org and to a lesser extent (www.)saveadullam.org have been down from (two different networks in) Israel. Over a period of minutes or seconds, ...
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1answer
136 views

Website slowed down, possible DDOS attack

I'm facing a big problem today. My website is very slow. I've tried everything and nothing helped. I disabled mysql and my website was still slow loading a static page. I also restarted the server. I ...
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1answer
145 views

Server Recovery from Denial of Service

I'm looking at a server that might be misconfigured to handle Denial of Service. The database was knocked offline after the attack, and was unable to restart itself after it failed to restart when the ...
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1answer
162 views

Single IP attack or other issue?

Description of incident: I notice in my MRTG panel that httpd processes have climbed to 800 ( our maximum ), but all other parameters are normal ( cpu, memory, traffic ) I immediately ran a nestat ...
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1answer
34 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 ...
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0answers
180 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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43 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
1k views

postfix queue active and mail transport unavailable

I am not very familiar with postfix, but I am pretty sure that what I am seeing in my logs is not a good thing, and I was hoping someone here might be able to shed some light on what is going on and ...
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135 views

sshd running at 100%

I'm running an Ubuntu/WordPress server on Amazon EC2 which is experiencing problems every 24-48 hours: I get a CPU alarm from EC2, log into the server, and discover sshd is running at 99.9% CPU. This ...
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127 views

Can someone give me advice on these rules to prevent DDOS where fragmented packets are sent without the initial SYN fragment ?

iptables -N NEW_TCP_PACKETS_NO_SYN iptables -A INPUT NEW_TCP_PACKETS_NO_SYN -p tcp ! --syn -m state --state NEW -m limit --limit 10/day -j LOG --log-prefix "New packets but not syn:" iptables ...
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62 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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50 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 ...
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362 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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116 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 ...
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181 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 ...
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0answers
96 views

Drop in HAproxy traffic with increase in connections

We have an intermittent issue that involves a severe drop in network traffic (both IN and OUT) on our HAProxy load balancer. It happens a couple times a day. HAProxy is configured to limit requests ...
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0answers
143 views

What advantages does mod_evasive have over mod_security2 in terms of DDOS protection?

I'm running an Apache2 server in front of a Tomcat and I need to implement a DDoS protection mechanism on the Apache2 layer. I have two candidates: mod_evasive and mod_security2 with the OWASP core ...
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151 views

DDoS attack simulation using MININET

I´m developing some dynamic security policies using SDN, one of them consist in how the network should respond to a DDoS attack detection. So, I would like to test my policies but I'm having some ...
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158 views

server reached MaxClients setting, consider raising the MaxClients setting

this is my mod-status report. Do you think I could be under a DDOS attack? Thanks Current Time: Monday, 14-Oct-2013 18:56:57 CEST Restart Time: Monday, 14-Oct-2013 18:54:48 CEST Parent Server ...
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0answers
20 views

Intelligently filtering bogus query strings

A vBulletin site I maintain is on the wrong end of a DoS attack which is inexplicably routing through CloudFlare unimpeded by their DoS protection. The requests look like this: 1 /?ZZZZCQG=XJXAUD ...
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270 views

Blocking a TCP Syn Attack

I have recently experienced a TCP Syn attack and since it was from a software like LOIC, it kept happening until I banned the IP Addresses or stopped my system from making output to them. Here is what ...
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0answers
276 views

How to protect Nginx from HULK DoS tool

There is a tool called HULK (Http Unbearable Load King). It's a web server denial of service tool. It is designed to generate volumes of unique and obfuscated traffic at a webserver, bypassing caching ...
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200 views

Block incoming DNS queries using netsh advfirewall

How do you do this with Windows firewall? iptables -I INPUT --in-interface ! lo -p udp --dport 53 -j DROP Ideally, if you can do this with netsh and so that it will survive whatever it is that ...
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112 views

Imagemagick/File upload abuse causing my memory errors

I had been running out of memory on my server lately and I noticed some individuals uploading the same "file" over and over in quick succession which locks up my instance of mini_magick. Eventually ...
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115 views

Delay response from apache when loaded with requests

So currently a bot hammers our server and causes high server load / dropped responses. I don't want to stop the bot as it has a purpose but I would like to slow it down. I've implemented squid to ...