CS & IT Solutions

Considering that there is a fairly big amount of DDoS attacks going around and not so many free tools available to work against this on a server level everyone will try to get the best of what he has available and why not use IPtables if you are on a Unix server.

Trying to check for an easy way to stop a DDoS attack and do not involve php or such scripts i ended up learning something about IPtables and that is that it is fairly simple to use TTL and Length of packets to stop or at least bring down to a reasonable amount an attack. This does not work all the time but for the last two times worked pretty well and this because of the bots that are being used to tun the attack.

As a first thing we should try and find out a few IPs that are being used to attack the server and this can easy be done using netstat like:

netstat -tn --inet 2>/dev/null | grep ":80" | \ awk '/tcp[\ ]*[0-9]+[\ ]*[0-9]+[\ ]+[^\ ]+[\ ]*[^\ ]*/ {print $5}' | \ cut -d":" -f1 | sort | uniq -c | sort -n

or more simple:

netstat -ntu | awk '{print $5}' | cut -d: -f1 | sort | uniq -c | sort -n

The IPs with a high connections number(eg. over 150) can be considered as being part of the attack even if a big intensity attack will make you see IPs with over 600-700 connections. Read the rest of this entry »

If you want to protect your apache webserver against DOS,DDOS or brute force attacks use mod_evasive module.mod_evasive is an evasive maneuvers module for Apache to provide evasive action in the event of an HTTP DoS or DDoS attack or brute force attack. It is also designed to be a detection and network management tool, and can be easily configured to talk to ipchains, firewalls, routers, and etcetera. mod_evasive presently reports abuses via email and syslog facilities.

Detection is performed by creating an internal dynamic hash table of IP Addresses and URIs, and denying any single IP address from any of the following:

* Requesting the same page more than a few times per second
* Making more than 50 concurrent requests on the same child per second
* Making any requests while temporarily blacklisted (on a blocking list)

This method has worked well in both single-server script attacks as well as distributed attacks, but just like other evasive tools, is only as useful to the point of bandwidth and processor consumption (e.g. the amount of bandwidth and processor required to receive/process/respond to invalid requests), which is why it’s a good idea to integrate this with your firewalls and routers for maximum protection.

This module instantiates for each listener individually, and therefore has a built-in cleanup mechanism and scaling capabilities. Because of this per-child design, legitimate requests are never compromised (even from proxies and NAT addresses) but only scripted attacks. Even a user repeatedly clicking on ‘reload’ should not be affected unless they do it maliciously. mod_evasive is fully tweakable through the Apache configuration file, easy to incorporate into your web server, and easy to use.

Install mod_evasive in Debian

#apt-get install libapache2-mod-evasive

This will complete the installation

Test mod_evasive Module

open any browser,open your apache server home page, and click the reload button as fast as you can.

source here

In this article I am trying to explain what DDOS is and how it can be prevented. DDOS happens due to lack of security awareness of the network/server owners. On a daily basis we hear that a particular machine is under DDOS attack or NOC has unplugged the machine due to DDOS attack . So DDOS has become one of the common issues in this electronics world. DDOS is like a disease which doesn’t have an anti-viral developed. So we should be carefull while dealing with it . Never take it lightly. In this article i am trying to explain the steps/measures which will help us defend from DDOS attack ,up to a certain extend .

What is a DDOS attack?

Simply said, DDOS is an advanced version of DOS attack . Like DOS , DDOS also tries to deny the important services running on a server by broadcasting packets to the destination server in a way that the Destination server cannot handle it. The speciality of the DDOS is that, it relays attacks not from a single network/host like DOS. The DDOS attack will be launched from different dynamic networks which has already been compromised.

Normally, DDOS consists of 3 parts . One is the Master ,Other the slave and atlast the victim. The master is the attack launcher ie the person/machine behind all this,sound’s COOL right . The slave is the network which is being compromised by the Master and Victim is the target site/server . Master informs the compromised machines, so called slaves to launch attack on the victim’s site/machine. Hence its also called co-ordinated attack.

In my term, Master is said to be the Master Brain, Slave is said to be the launch pad for the attack and Victim is the target.

How do they Do it? Read the rest of this entry »