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DDOS, or Distributed Denial of Service is an advanced version of DOS(Denial of Service) attack. Like DOS, DDOS also tries to deny 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 . The Master, the slave and at last the victim. The master is the attack launcher, i.e the person/machine behind all this. The slave is the network that 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.
Here is how I see it. Master is the Master Brain, Slave is said to be the launch pad for the attack and Victim is the target.
DDOS is done in 2 phases. In the first phase they try to compromise weak machines in different networks around the world. This phase is called Intrusion Phase. Its in the next phase, that they install DDOS tools and start attacking the victims machines/site. This Phase is called Distributed DoS attack phase.
What Allowed them to do it? Simple.
To find the load just use the command w or uptime -
To find if there is large number of HTTP process running use the command " ps -aux|grep HTTP|wc -l "
In a heavy server , the number of connections will go above 100. But during DDOS attack, the number will go even higher and thats when we need to find out from which all networks are these attacks coming. In DDOS the host machine doesn't have much importance. Its the network which is of importance here because, an attacker will use any machine on the compromised network or even will use all the machines in the network. Hence network address is of importance while fighting with the attack.
At command prompt execute the below command
Check each block of ips. Lets assume you have more than 30 connection from a single ip. Under normal cases there is no need for that many number of connection requests from a single IP. Try to identify such ips/networks from the list you get
If more than 5 host/ip connects from the same network then its a clear sign of DDOS .
Block that ips/networks using iptables /Apf
If you have APF, then just add the IPs which you want to block in the file /etc/apf/deny_hosts.rules
Continue this process untill the attack on the machine gets reduced. There is no complete or perfect solution to DDOS . The logic is simple, NO software or measures could handle attacks from multiple servers say from 50 - 100 servers all at a time. All that can be done is to take preventive measures .
Prevention is better than cure. Its very much true in the case of DDOS . In my Introduction, I had mentioned that DDOS happens because of vulnerable softwares/applications running on a machines in a particular network. Attackers use those security holes to compromise the servers in different network and install the DDOS tools (eg trinoo -DDOS tool).
Steps to Install APF
Notes: Go through the Document in the Apf and configure it for your needs. All configuration is set at conf.apf which is normally located at /etc/apf/conf.apf
Enable Anit-DOS mode in Apf (ie in conf.apf) . Also make sure that your root's cron has an entry like the one below
(b) Untar it
(d) Then execute
(e) Final steps to install
(f) Now the main step. To configure AIDE. AIDE stores all its rule sets in the file called aide.conf. To get more details on how to configure from 'man aide.conf'
(g) Here is a sample short aide.conf:
In this configuration, a rule called "Rule" is set to check permissions (p), inode (i), user (u), group (g), number of links (n), size (s), and md5 checksum (md5). This rules are applied to all files in /bin, /sbin, /var, and /usr/local/apache/conf because they should rarely if ever change. Files in /etc are checked for changes in only permissions, inode, user, and group because their size may change, but other things shouldn't. Files and directories in /var/spool and /var/log are not checked because those are folders where maximum updation takes place.
(h) After configuring AIDE should be initiated with all these rules.
For that execute
Use tools like RKDET(vancouver-webpages.com/rkdet), RKHUNTER(www.rootkit.nl) and CHKROOTKIT(www.chkrootkit.org) to find if any rootkit has been already installed and to locate the effected binaries in the machine, if any.
This is a simple Audit check List to check for.
Machines new or old should only be allowed to run on your network, if your Security Admin or DSE (Dedicated Security Expert) member approves it with status ``OK-to go live'' after auditing the box. All Host in the network should be checked on a regular basis by your DSE team to make sure that all hosts are up-to-date and can fight any attacks.
Use Open Source Tools like NESSUS (www.nessus.org), NMAP(www.insecure.org/nmap),
(link dead, sorry)
) for auditing a network to find its vulnerabilities.
Collect your networks and hosts data . Analysis them and study them to see from where and what kind of attacks are coming into the network. This step will help us to understand what kind of attacks we are facing and will help us to strengthen the preventive measures. Let me tell you this move is worth the money you spend,for sure.
Add this code to this file:
Mod_dosevasive is module for Apache to perform evasive action in the event of an HTTP DDoS attack or brute force attack. Please find the installation step of mod_dosevasive in DSO mode below
Eg: Install Mod_dosevasive
``$APACHE_ROOT'' is a variable that stores the location of the apache installation (eg $APACHE_ROOT =/usr/local/apache)
After this add the below code in httpd.conf
Then restart Apache
Since DDOS normally targets HTTP. Its always good to have a filtering system for apache . So that the request gets analyzed before web server handles it. Please find the installation step of mod_security in DSO mode below
Create a file named mod_security.conf under the folder /usr/local/apache/conf
Create the rule with reference to the link http://www.modsecurity.org/documentation/quick-examples.html and add it in the mod_security.conf file.
Add the location of mod_security.conf to httpd.conf
by adding the string below
This is the most important part. People, including users should be Security conscious. Only then will they understand the importance of Security measures . Server owner's and users should be made aware of the issues which can rise due to bad security measures.
Blessen Cherian works in Bobcares. He is passionate about Server Security and looks forward to gain expertise in this area.
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More Articles by Blessen Cherian © 2012-07-13 Blessen Cherian
Software engineering is the part of computer science which is too difficult for the computer scientist. (Friedrich Bauer)