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Webserver banner grabbing and countermeasures

Webserver Banner grabbing or fingerprinting is the method of gaining information about the target host OS. web server type, version etc. Once the hacker gets the needed information about the target OS etc, he can easily find out the vulnerabilities present in particular version and launch his attacks against it. Today we are going to see how webserver banner grabbing is performed on web servers and how to apply counter measures to it. We will see Apache and IIS 8 server examples in this article.

Apache:

Imagine I have set up a website named www.shunya.com on an Apache server. A hacker can easily find Information about the web server in different ways. For example, a hacker can visit the website and and try to open a webpage which is not existent on my server, like below.

In the above example, hacker tried to open page named “admin.php” which was not available on my server and in turn the server responded with a type of web server, the target OS and the scripting language. This is giving out too much information.

The traditional and popular way of fingerprinting is through telnet. A hacker opens command line or terminal. and types the command “telnet www.shunya.com 80″. When the screen goes black, type “HEAD / HTTP/1.0″ and this will give the server information.

There are also many fingerprinting tools available. I am gonna show you only one, Id serve. Let’s see how to banner grab using Id serve.

Now what are the preventive measures we can take in Apache server to disable or atleast prevent fingerprinting to some extent. Apache web server has a configuration file called “httpd.conf” where we can make changes to fight fingerprinting. Go to httpd.conf and change the value of the option “Server Signature  to off”. This will not display any information about server when an nonexistent page has been accessed.

In the httpd.conf file, changing the value of “Server Tokens” from “Full” to “Prod” will only show the minimum server information as shown below.

This still discloses that our web server is Apache but it doesn’t show the version. In Kautilya’s words this is delaying the march of enemy. Here are the options we set.

IIS 8:

Now imagine we changed our www.shunya.com website from Apache server to the latest version of Microsoft web server, IIS 8. To prevent error pages form revealing any information in IIS server, we can set custom error pages.  Now let’s use IDserve tool to fingerprint the IIS 8 server.

It shows the server version. Now how can we prevent this. Microsoft provides a tool named UrlScan freely available for download which can be used easily to process HTTP requests. Download this tool and install it. ( See how to configure Urlscan for IIS 7.5 and IIS 8 ). Then go to the configuration file of UrlScan, “UrlScan.ini” located at “C:WindowsSystem32inetservUrlscan” by default and change the value of “RemoveServerHeader’ from “0″ to “1″.

This will not reveal the server version information as shown below.

We can further mislead the attacker by setting our server name to some other value different than our original one. This can be done by setting the value of “RemoveServerHeader” to “0 “and changing the value of “AlternateServerName” to the value we want to specify ( in our example Nginx ).

So when the attacker tries to fingerprint our website, he will be misleaded.

Note: Taking this preventive measures will not stop a determined hacker to find out our server information.

That’s all in webserver banner grabbing and countermeasures.

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Setting up Web Server in Ubuntu Server

In this article, we are going to see how to set up a web server in Ubuntu Server. Before that, I want to give  credit for this article to Mike of www.funwithlinux.net. I learnt how to install the web server from this article, made some mistakes initially but finally successful.

What is a web server? It is a server which hosts websites. Each and every website has a  server. Most web servers are set up on Linux for the primary reason that it is free. I am going to set up my web server on Ubuntu Server 12.04.

To set up a web server we are going to install four components, Apache (server software), PHP (scripting language used to create webpages), MYSQL (database), PHP-MYSQL (MySQL support in PHP ). Login as root into Ubuntu server.

In the terminal type “apt-get install apache2″ to install Apache package. Type ‘Y’ when system prompts you to continue.

To check whether apache packages have been installed or not type the command “wget localhost index.html” in the terminal. This will download the index.html file to the local directory. Type “ls” to see if the file has been downloaded or not. If it is present, apache has been correctly installed.

The apache2 config file is located at “/etc/apache2/”. In this same directory we have a directory named ‘conf.d’. Configuration files( files with the suffix .conf ) in this directory will be parsed by apache2 during startup.  If we intend to run multiple sites from the same server, we need to put our config files here. Let’s create a file name “shunya.com.conf”.

In the file shunya.com.conf, add the following text and save the file. The first line tells  Apache to  listen on port 80. The second line shows the ServerAdmin and is optional. The third line shows our web server’s root directory. The fourth line is host header Apache2 will listen for, as sent by the end user’s browser. The fifth line is the file used for logging errors. This line is also optional but is very helpful.  The settings not configured under <VirtualHost> tags will be inherited from apache2.conf or other configuration files. Close the file by typing “:wq”.

As we created the config file of our host, we need to create our root directory referenced in the config file i.e “/var/www/shunya.com”. Navigate to the directory by typing “cd /var/www/”. Create new directory named ‘shunya.com’ by typing “mkdir shunya.com”. Make the root user the owner of the directory by typing the command “chown root:www-data /var/www/shunya.com -R”. Make this directory readable and executable by typing the command “chmod 550 /var/www/shunya.com -R”.

Create a file named index.php in our root directory shunya.com.

Edit the file as below. We will echo some Archimedes in our index.php file. Save and exit the file.

Next, we have to install PHP. Type the command “apt-get install php5″. Type Y at appropriate prompts.

Reload the apache config file by typing “service apache2 reload”. Then restart the apache service using “service apache2 restart”.

Let’s see if our website is working. From a remote machine which has access to your web server open the browser and type the IP address of the web server. If we get “Eureka Eureka” displayed, then our server is working.

Install MySQL server by typing “apt-get install mysql-server”. 

The system will prompt you to set a root user password for MYSQL. Set the password and confirm it again.

Type the command “apt-get install php5-mysql” to install MySQL support for PHP.

We have set up our web server successfully.