Category: Cpanel and WHM

Distributed Denial of service(DDOS)

On June 10, 2012

In Cpanel and WHM, Linux server, Plesk, Windows Server

A denial-of-service attack (DoS attack) or distributed denial-of-service attack (DDoS attack) is an attempt to make a computer or network resource unavailable to its intended users. 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.

Types:-

Ping of death :-
Attacker deliverately sending a ping packet, normally 64 bytes, that is larger than the 65,535 bytes. Many computer systems cannot handle an IP packet larger than the maximum IP packet size of 65,535, and often causes computer systems crash. A ping packet of size greater than 65,535, can be sent if it is fragmented.When a receiving computer reassembles the packet, a buffer overflow occurs, which often causes computer to crash.

Ping of flood:-
An attacker overwhelming the victim’s network with ICMP Echo Request (ping) packets. A flood of ping traffic can consume singificant bandwidth on low to mid-speed networks bringing down a network to a crawl.

Smurf Attack:-
Smurf attack exploits the target by sending repeated ping request to broadcast address of the target network. The ping request packet often uses forged IP address (return address), which is the target site that is to receive the denial of service attack. The result will be lots of ping replies flooding back to the innocent, spoofed host. If number of hosts replying to the ping request is large enough, the network will no longer be able to receive real traffic.

SYN Floods :-
When establishing a session between TCP client and server, a hand-shaking message exchange occurs betwen a server and client. A session setup packet contains a SYN field that identifies the sequence in the message exchange. An attacker may send a flood of connection request and do not respond to the replies, which leaves the request packets in the buffer so that legitimate connection request can’t be accommodated.

Teardrop Attack :-
Teardrop attack exploits by sending IP fragment packets that are difficult to reassemble. A fragment packet identifies an offset that is used to assemble the entire packet to be reassembled by the receiving system. In the teardrop attack, the attacker’s IP puts a confusing offset value in the sebsequent fragments and if the receiving system doesn’t know how to handle such situation, it may cause the system to crash.

Prevetion:-

1. Install Intrusion Detection System (IDS)
2. Implement Sysctl. Prevent ping attacks (ping of death, ping of flood, and smurf attacks) by disabling ping responses on the network machines. Enable IP Spoofing protection, and TCP SYN Cookie Protection.
3. Install advanced firewall and DDoS utilities.
4. Install Apache mod_evasive and mod_security modules to protect against HTTP DDoS attacks.

Mod_security:-
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.

Mod_evasive:-
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:

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

Note:-
1. Well there are no 100% prevention or protection against DDOS.
2. This steps won’t be enough if the DDOS attack is of very high volume.

How dns works

By wahab

On June 10, 2012

In Cpanel and WHM, Linux server, Plesk, Windows Server

A DNS client “resolves” an IP address by sending a specially formatted request to a DNS server. The client has to know the address of one or more DNS servers in advance. The reply from the server may be a direct reply with the IP address associated with the hostname, a referral to another DNS server, or a response indicating the requested name can’t be found in DNS.

Typically, the request will ask the server to “recursive“, i.e. if it cannot answer the question from its own local memory, it should go ask other servers on behalf of the client. This behavior helps the local server build up its own cache of addresses frequently looked up.

Another form of query is called iterative query, where a client machine sends the request to a known DNS server , if that DNS server fail to resolve the domain name into a IP, then the client sends the request to another DNS and this process goes on and on until it get the required IP resolution by sending address resolution request to all its known DNS.If every known DNS fail to give the IP, then client goes to the root domain.

When you type a URL into your browser, it uses the following steps to locate the correct website:

A DNS client uses a resolver to request resolution of a host name to an IP address. The resolver is really just a special-purpose application that’s sole function is to act as an intermediary between name servers and various applications that need name resolution, such as Web browsers, e-mail applications, and so on. Here’s an example: Assume you fire up your browser and direct it to connect to www.mysite.com.

1. Your browser checks it’s cache (memory) to see if it knows which IP address the domain name resolves to. If it knows, it will resolve it and display the web page.
2. If the domain name is unable to be resolved, the browser will check your hosts file for a DNS entry.
3. If there’s no entry in the hosts file, the browser will check the default DNS server (specified via your computer’s network settings, /etc/resolv.conf). This is usually your ISP’s DNS server or your employer’s. If the default DNS server has an entry for that domain name, the browser will display the applicable website.
4. If the default name server has no cached results, it sends a DNS query to the root server for the .com domain.
5. The root server responds with the addresses of the name servers that are authoritative for the mysite.com domain.
6. Your ISP’s name server then builds another request for www.mysite.com and submits it to mysite.com’s name server, which responds with the IP address of www.mysite.com.
7. That information is passed back to your resolver, which passes it to your application.

Case insensitive url Aapche Webserver

By wahab

On June 10, 2012

In Cpanel and WHM, Linux server, Plesk

How to enable Case-Insensitive url’s ?

Webserver: Apache

OS: Linux

One of our customer had opened ticket. He has a very interesting need. He wants his site urls to be Case-insensitive . I will explain with examples:- He needs the following urls to work currently he is getting 404 errors for each request.

http://yourdomain.com/Yourpage.html

http://yourdomain.com/YourPage.html

We were unable to add rewrite rules in his htaccess files as we need to write rule for every single file that has a mixture of upper and lower case.

http://yourdomain.com/yourpage.html => This is the correct url

He needs this url http://yourdomain.com/Yourpage.html to load even if they have one spelling mistake or there is one capitalization error. This was found very strange. We have managed to fix the issue by adding an apache module server wide, which neutralise all the the upper case and lower case characters to a single format.

Solution: If you want requested URLs to be valid whether uppercase or lowercase letters are used and with one spelling mistake, “mod_speling” module needs to be enabled in apache.

The mod_speling module is part of the standard Apache distribution but is not enabled by default, so you need to explicitly enable it. When mod_speling is installed, it may be turned on for a particular scope (such as a directory, virtual host, or the entire server) by setting the CheckSpelling directive to On.

For making URL case-insensitive in cPanel:

First run belwow on Cpanel based server : /scripts/easyapache And select ‘Spelling’ from the available module list for apache. Once apache/php are recompiled with this option and easyapache finishes, you can put below code in the .htaccess or in the virtual host entry of the particular domain to apply it to any directory/directories :

< IfModule mod_speling.c > CheckCaseOnly On CheckSpelling On < / IfModule > This helped to fix this particular issue

Verify PHP/cURL is working correctly

By wahab

On February 15, 2012

In Cpanel and WHM, Linux server, Windows Server

Simply, cURL is a command line tool for getting or sending files using URL syntax. It supports a range of common Internet protocols, including HTTP, FTP, SCP, SFTP, TFTP, TELNET, FILE, IMAP, POP3, SMTP and RTSP, etc. The command is designed to work without user interaction.

Usage:-

Basic use of cURL involves simply typing curl at the command line, followed by the URL of the output to retrieve.
To retrieve the google.com homepage, type:
curl www.google.com
What is PHP/CURL?
The module for PHP that makes it possible for PHP programs to access curl-functions from within PHP.

How to verify cURL is working correctly?.

cURL does have very powerfull functions which inturn not used properly may leads to complete breakdown of your server. Because of this most of the hosting companies disable some of these dangerous functions. But for a PHP Programmer cURL is an essential tool and must requires basic functionality atleast. It is very easy to check the PHP/cURL is working normal.

Steps:-

1. Create a php file “check_cURL.php” with following content using any of your favourite editor.

<?php
/**
* Initialize the cURL session
*/
$ch = curl_init();
/**
* Set the URL of the page or file to download.
*/
curl_setopt($ch, CURLOPT_URL,
‘http://news.google.com/news?hl=en&topic=t&output=rss’);
/**
* Create a new file
*/
$fp = fopen(‘rss.xml’, ‘w’);
/**
* Ask cURL to write the contents to a file
*/
curl_setopt($ch, CURLOPT_FILE, $fp);
/**
* Execute the cURL session
*/
curl_exec ($ch);
/**
* Close cURL session and file
*/
curl_close ($ch);
fclose($fp);
?>

2. Execute the “check_cURL.php” script (I just run “php -q check_cURL.php” from the terminal)

3. Check the output file “rss.xml”. If the file contains data, we can conclude curl is working fine.

How does this script works:-

The check_cURL.php is simple php script which when called connects to the url specified(Google in our example) and download its source code. The script then writes its output to downloaded content to the output file(rss.xml in our example).

IPTABLES complete cheatlist

By wahab

On November 17, 2011

In Cpanel and WHM, Linux server, Plesk

Please note that the iptables rules are stored in the /etc/sysconfig/iptables file. If you view this file, you’ll see all the default rules.

1. Delete Existing Rules

Before you start building new set of rules, you might want to clean-up all the default rules, and existing rules. Use the iptables flush command as shown below to do this.

iptables -F
(or)
iptables –flush
service iptables save

2. Set Default Chain Policies

The default chain policy is ACCEPT. Change this to DROP for all INPUT, FORWARD, and OUTPUT chains as shown below.

iptables -P INPUT DROP
iptables -P FORWARD DROP
iptables -P OUTPUT DROP

When you make both INPUT, and OUTPUT chain’s default policy as DROP, for every firewall rule requirement you have, you should define two rules. i.e one for incoming andone for outgoing.
Change default policy for INPUT/OUTPUT/FORWARD to ACCEPT. All inbound connections will be allowed

iptables -P INPUT ACCEPT
iptables -P OUTPUT ACCEPT
iptables -P FORWARD ACCEPT

3.Block an IP for inbound connection

iptables -A INPUT -s 192.168.1.5 -j DROP
iptables -A INPUT -i eth0 -p tcp -s “$BLOCK_THIS_IP” -j DROP
4.Allow an IP for inbound connection

iptables -A INPUT -s 192.168.1.5 -j ACCEPT

5.Block outbound IP address

iptables -A OUTPUT -d <IP> -j DROP

6.Block outbound PORT

iptables -A OUTPUT -p tcp –dport <PORT> -j DROP

7.Block outbound IP:PORT

iptables -A OUTPUT -p tcp -d <IP> –dport <PORT> -j DROP

8.Allow port 2222 for inbound tcp connections

iptables -A INPUT -p tcp –dport 2222 -j ACCEPT

9.White list an IP

iptables -A INPUT -i eth0 -s <IP> -j ACCEPT

10.Open port 5666

iptables -I INPUT -p tcp -m tcp –dport 5666 -j ACCEPT
11.Allow ALL Incoming SSH

The following rules allow ALL incoming ssh connections on eth0 interface.

iptables -A INPUT -i eth0 -p tcp –dport 22 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp –sport 22 -m state –state ESTABLISHED -j ACCEPT

12.Allow Incoming SSH only from a Sepcific Network

The following rules allow incoming ssh connections only from 192.168.100.X network.

iptables -A INPUT -i eth0 -p tcp -s 192.168.100.0/24 –dport 22 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp –sport 22 -m state –state ESTABLISHED -j ACCEPT

In the above example, instead of /24, you can also use the full subnet mask. i.e “192.168.100.0/255.255.255.0″.

13. Allow Incoming HTTP and HTTPS

The following rules allow all incoming web traffic. i.e HTTP traffic to port 80.

iptables -A INPUT -i eth0 -p tcp –dport 80 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp –sport 80 -m state –state ESTABLISHED -j ACCEPT

The following rules allow all incoming secure web traffic. i.e HTTPS traffic to port 443.

iptables -A INPUT -i eth0 -p tcp –dport 443 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp –sport 443 -m state –state ESTABLISHED -j ACCEPT

14.Combine Multiple Rules Together using MultiPorts

When you are allowing incoming connections from outside world to multiple ports, instead of writing individual rules for each and every port, you can combine them together using the multiport extension as shown below.

The following example allows all incoming SSH, HTTP and HTTPS traffic.

iptables -A INPUT -i eth0 -p tcp -m multiport –dports 22,80,443 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp -m multiport –sports 22,80,443 -m state –state ESTABLISHED -j ACCEPT

15.Allow Outgoing SSH

The following rules allow outgoing ssh connection. i.e When you ssh from inside to an outside server.

iptables -A OUTPUT -o eth0 -p tcp –dport 22 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A INPUT -i eth0 -p tcp –sport 22 -m state –state ESTABLISHED -j ACCEPT

Please note that this is slightly different than the incoming rule. i.e We allow both the NEW and ESTABLISHED state on the OUTPUT chain, and only ESTABLISHED state on the INPUT chain. For the incoming rule, it is vice versa.

16.Allow Outgoing SSH only to a Specific Network

The following rules allow outgoing ssh connection only to a specific network. i.e You an ssh only to 192.168.100.0/24 network from the inside.

iptables -A OUTPUT -o eth0 -p tcp -d 192.168.100.0/24 –dport 22 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A INPUT -i eth0 -p tcp –sport 22 -m state –state ESTABLISHED -j ACCEPT

17.Allow Ping from Outside to Inside

The following rules allow outside users to be able to ping your servers.
iptables -A OUTPUT -p icmp –icmp-type echo-request -j ACCEPT
iptables -A INPUT -p icmp –icmp-type echo-reply -j ACCEPT
19.Allow Loopback Access

You should allow full loopback access on your servers. i.e access using 127.0.0.1

iptables -A INPUT -i lo -j ACCEPT
iptables -A OUTPUT -o lo -j ACCEPT

20. Allow MySQL connection only from a specific network

iptables -A INPUT -i eth0 -p tcp -s 192.168.100.0/24 –dport 3306 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp –sport 3306 -m state –state ESTABLISHED -j ACCEPT

21.Prevent DoS Attack

The following iptables rule will help you prevent the Denial of Service (DoS) attack on your webserver.

iptables -A INPUT -p tcp –dport 80 -m limit –limit 25/minute –limit-burst 1000 -j ACCEPT
In the above example:
-m limit: This uses the limit iptables extension

–limit 25/minute: This limits only maximum of 25 connection per minute. Change this value based on your specific requirement
–limit-burst 1000: This value indicates that the limit/minute will be enforced only after the total number of connection have reached the limit-burst level.

22.Port forwarding using IPTables

Forward port 80 from IP address to another IP

iptables -t nat -A PREROUTING -i eth0 -p tcp –dport 80 -j DNAT –to <DESTIP>:80
iptables -t nat -A POSTROUTING -p tcp –dst <DESTIP> –dport 80 -j SNAT –to <SRCIP>
iptables -t nat -A OUTPUT –dst <SRC> -p tcp –dport 80 -j DNAT –to <DESTIP>:80

Removing the above rules
iptables -t nat -D PREROUTING -i eth0 -p tcp –dport 80 -j DNAT –to <DESTIP>:80
iptables -t nat -D POSTROUTING -p tcp –dst <DESTIP> –dport 80 -j SNAT –to <SRCIP>
iptables -t nat -d OUTPUT –dst <SRC> -p tcp –dport 80 -j DNAT –to <DESTIP>:80

23.List all the rules in the iptables

iptables -L

24.Check an IP in the rule

iptables -nL | grep <IP>

25.Save the current iptables rules

iptables-save > File_name

26.Restore iptable rules from the file

iptables-restore < File_name

MSSQL support to PHP in cpanel server

By wahab

On November 3, 2011

In Cpanel and WHM, Linux server

To use the MSSQL extension on Unix/Linux, you first need to build and install the FreeTDS library. FreeTDS is a set of libraries for Unix and Linux that allows your programs to natively talk to Microsoft SQL Server and Sybase databases.

You can refer to the following url to get informations about mssql extension and the functions supported with it.
‘http://www.php.net/manual/en/book.mssql.php‘

To get these functions to work, you have to compile PHP with –with-mssql[=DIR] , where DIR is the FreeTDS install prefix. And FreeTDS should be compiled using
–enable-msdblib

Installation instruction:-

(This is not specific to cpanel servers, you can recompile php directly without easyapache in any normal linux servers with ‘–with-mssql=/usr/local/freetds’)

1-. Download freetds source -> www.freetds.org
2-. tar -zxvf freetds-stable-tgz
3-. cd freetds-*
4-. ./configure –prefix=/usr/local/freetds –with-tdsver=8.0 –enable-msdblib –with-gnu-ld

Note: If you use SQL 2000, 2005, 2008 then tds version = 8.0
if you use SQL 7.0 then tds version = 7.0

5-. make
6-. make install
7-. To check freetds working, run from terminal
7.1 /usr/local/freetds/bin/tsql -S <ip of the server> -U <User SQL>
7.2 If the connection parameters are correct you will be connected to a prompt.
8-. Add the following text in freetds.conf ( /usr/local/freetds/etc )
[TDS]
host = <ip of the Server with Sql>
port = 1433
tds version = 8.0

9-. Add the following line in the file /etc/ld.so.conf and run ldconfig -v:
include /usr/local/freetds/lib

10-. Recompile PHP with –with-mssql=/usr/local/freetds flag.
Create a file called all_php4 or all_php5 in:

‘/var/cpanel/easy/apache/rawopts/’

The file doesnt exist by default, just create it and add this line to the file:
–with-mssql=/usr/local/freetds
Easy apache will check this file ‘/var/cpanel/easy/apache/rawopts/all_php5’ for any additional php configuration option during recompilation.

11-. Run ‘/scripts/easyapache’

Notes:-

1-. If you are running a 64bit OS and get an error about configure: error: ‘Could not find /usr/local/freetds/lib64/libsybdb.a|so’
then you need to do the following:
1.1 Make sure libsybdb.so is available on the server,then
1.2 ln -s /usr/local/freetds/lib/libsybdb.so.5 /usr/lib64/libsybdb.so.5
1.3 ln -s /usr/local/freetds/lib/libsybdb.so.5 /usr/local/freetds/lib64/libsybdb.so
1.4 Run ldconfig -v

2-. If you are getting an error about configure:’ error: Directory /usr/local/freetds is not a FreeTDS installation directory’
2.1 cp [tds source]/include/tds.h /usr/local/freetds/include
2.2 cp [tds source]src/tds/.libs/libtds.a /usr/local/freetds/lib
2.3 Recompile again.

Reference:-

http://www.freetds.org/userguide/
http://www.php.net/manual/en/book.mssql.php
http://forums.cpanel.net

Joomla jos_session table crashed

By wahab

On June 26, 2011

In Cpanel and WHM, Linux server, Plesk

You may come across the following error sometime if you are working joomla site.
jtablesession::Store Failed
DB function failed with error number 145
Table ‘./eilmccco_cmsicdc/jos_session’ is marked as crashed and should be repaired SQL=INSERT INTO jos_session ( `session_id`,`time`,`username`,`gid`,`guest`,`clie nt_id` ) VALUES ( ‘ca7331cb8a008d79e24df425257229ea’,’1227636484′,” ,’0′,’1′,’0′ )

This is a very common error. The problem with this error is that you cannot access your site nor the admin page.
The error messages means that the table “jos_session” is crashed or damaged. This table stores your session information.

This issue can be easily fixed by repairing the session table. For doing this the first thing you should do is find out your joomla database. This can be done by checking your joomla configuration.php file.
Now we can try repairing the table in following ways.

Cpanel
If you are using the Cpanel, then you can repair you joomla database by clicking the “Repair DB” option in the Mysql section of the Cpanel.

phpMyAdmin

If you can access your database though phpMyAdmin, then on the phpMyAdmin interface, select the joomla database and look for the table “jos_session”. Once you selected the “jos_session” (tick the checkbox) and choose “Repair table” from the drop-down you find at the bottom of the list of tables.

SSH access

If you have shell access of your server, the database can be repaired within the Mysql.
Login to the mysql with necessary privileges
#mysql -u <dbuser> -p
mysql> use joomla1; [Assume your joomla database name is joomla1]
mysql> REPAIR TABLE jos_session;

If all the above tricks failed, then you must recreate the “jos_session” table

First of all, please take a complete backup of the joomla database.

phpMyAdmin

1 – Go to MySQL phpMyadmin Control Panel

2 – Go and click on “SQL” near the top left corner of the page, and paste the following lines (below) into the empty text area :

DROP TABLE IF EXISTS `jos_session`;
CREATE TABLE `jos_session` (
`username` varchar(150) default ”,
`time` varchar(14) default ”,
`session_id` varchar(200) NOT NULL default ‘0’,
`guest` tinyint(4) default ‘1’,
`userid` int(11) default ‘0’,
`usertype` varchar(50) default ”,
`gid` tinyint(3) unsigned NOT NULL default ‘0’,
`client_id` tinyint(3) unsigned NOT NULL default ‘0’,
`data` longtext,
PRIMARY KEY (`session_id`(64)),
KEY `whosonline` (`guest`,`usertype`),
KEY `userid` (`userid`),
KEY `time` (`time`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8;

3 – Click on “Execute” or “Go” to execute the command.

Thats it. This must fix your concern…

Please let me know your feedback and also if you have any other easy workaround