Building a secure web server

To create the most secure web server we need the following:

• Create a sandbox chroot with debootstrap
• sandbox apache2, php5, mysql
• install and configure mod-security2, as well as edit the necessary directives in the apache and php configuration files.

We take the Ubuntu distribution as a basis.

Create a chroot sandbox. First you need to add a new repository to sources.list and update the list of packages.

echo 'deb ubuntu.mirror.cambrium.nl/ubuntu/lucid main universe' >> /etc/apt/sources.list
apt-get update

Install debootstrap itself and create a nested OS - chroot sandbox:

apt-get install debootstrap

If the installation was successful then run the tool:

debootstrap --variant=buildd --arch i386 lucid /home/chroot archive.ubuntu.com/ubuntu/

Arguments are the following:

• architecture of the future system,
• distributor,
• directly to the directory that will serve as our chroot sandbox
• repository from which the utility should download the distribution.

Install mysql. The tricky thing is that the MySQL refuses to work correctly in the sandbox. You can do it easier. Install mysql in the main OS:

apt-get install mysql-server mysql-client

Then we edit the config (/etc/mysql/my.cnf) and change bind_address from 127.0.0.1 to 127.0.0.1

After these steps mysql will be available inside the sandbox, however, instead of localhost, you need to specify 127.0.0.1 as the mysql host.

Configure chroot. First you need to configure the resolver and the list of repositories for the chroot. Let’s execute the commands:

cp /etc/resolv.conf /home/chroot/etc/resolv.conf
cp /etc/apt/sources.list /home/chroot/etc/apt/sources.list

We forward system file systems into the chroot environment. To do this open the /etc/fstab file in your favorite editor and add the following lines to it:

/proc /home/chroot/proc none rbind 0 0
/dev /home/chroot/dev none rbind 0 0
/sys /home/chroot/sys none rbind 0 0

Save and mount:

mount -a

We are done in the main OS. Let’s run the last command in the main terminal to get into the chroot sandbox OS:

chroot /home/chroot

Let’s configure the OS inside the chroot. Run the familiar commands:

echo 'deb ubuntu.mirror.cambrium.nl/ubuntu/lucid main universe' >> /etc/apt/sources.list
apt-get update

Let’s move on to installing apache2 and php inside the chroot. The installation is not different from a regular installation, so I won’t dwell on this in detail (the libapache2-mod-security2 module is required to be installed):

apt-get install apache2 apache2-doc apache2-mpm-prefork apache2-utils libexpat1 ssl-cert libapache2-mod-security2
apt-get install libapache2-mod-php5 libapache2-mod-ruby php5 php5-common php5-curl php5-dev php5-gd php5-idn php-pear php5-imagick php5-imap php5-mcrypt php5-memcache php5-mhash php5- ming php5-mysql php5-pspell php5-recode php5-snmp php5-sqlite php5-tidy php5-xmlrpc php5-xsl

The final stage. apache2 configuration, php, libapache2-mod-security2. Create an apache user and user directory:

cd/; mkdir -m 755 web
useradd dot -b /web -m -U -s /bin/false
chmod 754 /web/dot
mkdir -p -m 754 /web/dot/public_html/www
mkdir -p -m 777 /web/dot/tmp
chmod +t /web/dot/tmp
chown -R dot:dot /web/dot/

So we’ve created a user, disabled it, created a home directory, created a web directory, created a personal temporary directory and recursively changed the directory’s owner.

Got to edit the default virtual host for our user:

nano /etc/apache2/sites-enabled/000-default

Context:

<VirtualHost *:80>
DocumentRoot "/web/dot/public_html/www/"
ServerName dot
ErrorLog /web/dot/error_log
CustomLog /web/dot/access_log combined

We change the default user and group from which apache will run. To do this, edit the apache2 configuration file:

nano /etc/apache2/apache2.conf

User www-data
group dot

Add some directives to the end of the file:

# Disable the signature at the bottom of the apache service pages (404 error page, etc.)
ServerSignature Off
# Server response in the header (Prod value will display only the name of the software - Apache)
ServerTokensProd
#disable CGI scripts, disable symbolic links, disable directory browsing, disable SSI
Options -ExecCGI -FollowSymLinks -Indexes -Includes

Edit the php.ini configuration file:

nano /etc/php5/apache2/php.ini

Change the value of the following directives:

expose_php = Off
magic_quotes_gpc = On
register_globals = Off
disable_functions = popen,exec,system,passthru,proc_open,shell_exec,in i_restore,dl,symlink,chgrp,ini_set,putenv,extensio n_loaded,getmyuid, posix_setuid,posix_setsid,posix_setpgid,posix_kill ,apache_child_terminate,chmod,chdir,phpinfo
safe_mode = On
safe_mode_gid = On
open_basedir = "/web/dot/"

Configuring mod-security2 First, let’s create the necessary directories and files:

mkdir /etc/apache2/conf.d/modsec
mkdir /var/log/apache2/modsec
touch /etc/apache2/conf.d/modsec/modsecurity_crs_10_config.conf
touch /etc/apache2/conf.d/modsec/modsecurity_crs_15_customrules.conf

Next, edit the created files:

• modsecurity_crs_10_config.conf - file with basic module settings
• modsecurity_crs_15_customrules.conf - file with rules for the module

nano /etc/apache2/conf.d/modsec/modsecurity_crs_10_config.conf

Contexts:

# Enable filter engine
SecRuleEngine On
# Log only suspicious requests:
SecAuditEngine RelevantOnly
# Log file name
SecAuditLog /var/log/apache2/modsec/audit_log
# Output debug information
SecDebugLog /var/log/apache2/modsec/debug_log
SecDebugLogLevel 1
# For suspicious requests, write to the log by default:
# and return an HTTP response with a 403 code
SecDefaultAction log,auditlog,deny,status:403,phase:2

Second file:

nano /etc/apache2/conf.d/modsec/modsecurity_crs_15_customrules.conf

Contexts:

# Protection against LFI\read file
SecRule ARGS "\.\./"
SecRule ARGS "/etc.+passwd" "t:lowercase"
SecRule ARGS "/proc/.+" "t:lowercase"
# Protection against SQL injections
SecRule ARGS "delete.+from" "t:lowercase"
SecRule ARGS "insert.+into" "t:lowercase"
SecRule ARGS "select.+from" "t:lowercase"
SecRule ARGS "union.+select" "t:lowercase"
SecRule ARGS "group_concat" "t:lowercase"
SecRule ARGS "information_schema" "t:lowercase"
SecRule ARGS "benchmark" "t:lowercase"
# Change the server response, the software is now not apache
SecServerSignature "Guess"

The above rules for the module are working, although they need to be improved, they are given as an example.