Category: Analysis

Analysis, Business, Cyber Security, Management

Awareness of Social Engineering

Aug 5, 2021 by BITS Media 0 Comments , , , , , , ,

Social engineering methods and means for obtaining information have been around for ages.

They seem like simple requests or benign coordinated events, but the truth is that social engineering often exploits your most valuable asset.  Your users.  A compromised user can then be used to wreak havoc or throw deeper hooks into the targeted network.  Most network hacks are incremental in nature with an attack vector that often times leads to a compromised user, admin, or super user.

The easiest way to penetrate, hack, or otherwise take-over a network is to start with the company directory. 

The simple example of a social engineering attack might be… ring ring, “hello, this is Joe with the helpdesk.  I am working on xyz what is your password?”  Social engineering methods are still the most prolific way for attackers to get deep within a network and allow attackers to simply go under the radar while they wreak havoc or steal sensitive data. 

A recent spear fishing attack on a US aerospace company leveraged the company directory and intricate email spoofing.  The attacker started a conversation from an email that looked like aerospacecompany.com’s email domain.  In other words the attacker had the name of a person in the organization with a valid email address and job title, and then registered aerospacecompanyUS.com, a similar looking email domain, to send users targeted malware.  They used the company directory and email domain to go deep and got a susceptible IT staff member to open a link and unknowingly involved in the attack.  Ultimately the attacker was able to get admin access to critical systems on the network.

It is important to maintain a user awareness and training posture for your organization.  Users and stakeholders need to be constantly reminded of internet and email etiquette as well as not to click on un-trusted links.  Your network cannot rely solely on technical measures to keep bad people out.  Even with anti-virus, anti-malware, updated browsers, and pop-up blockers a social engineering attack takes people and awareness to thwart.

Analysis, Business, Cyber Security, Management

Physical and Environmental Considerations

Aug 5, 2021 by BITS Media 0 Comments , , ,

The location and physical security of a server system is one of the first things to consider when putting a system online.  Your needs may not dictate that your server be in a secure Tier 4 co-location facility, but your servers may need to be at least in a locked and controlled access room in the back corner of your office suite.  The bottom line is that you can’t certify a system secure if it is in common access kitchen that you share with 4 other businesses.

Many IT departments have a safe place that they put the core of their network in.  Reliable power and cooling are needed to keep your systems running 24 hours a day 7 days a week.  If you are able to co-locate your servers with a service provider then make sure that you have the physical access that you need in case of emergency and after hours needs.  Service level agreements with your provider will help ensure that you get the help you need and that when something happens your organization is not left holding the bag.

Environmental concerns should be considered such as flooding and fire protection.  Hardware should be placed off the floor to prevent susceptibility to local water pipe flooding.  If you can place equipment higher than that, then you are even better off.  In 1997 one of the facilities that we were working at had a water main break in the back of the building.  Although the water main break was 10 feet below the ground, the water pressure created a large hole, compromised the concrete foundation of the building and mud and water poured into the rest of the building.  When workers arrived the next morning they found 6 inches of mud and muck throughout the building.  Though there was severe damage to the facility most critical equipment was spared simply because it was elevated off the ground.

Users desktops should also be elevated off the ground for the same reason.  Telecom equipment in data closets is typically wall mounted on back boards and should also be positioned at comfortable working heights well off the ground. 

Analysis, Business, Finanace, Management

Harden Windows Servers

Aug 5, 2021 by BITS Media 0 Comments ,

Windows Server  has new security features, best practice wizards, and sleeker interfaces to enhance the security posture of the operating system installation.  Windows Server has a major install base and is relevant to cover for server hardening. Most settings are similar and familiar between the different Windows desktop and server versions.

It should be noted that many of the advanced network management and security features require an Active Directory implementation to fully leverage.  As with any corporate network the security is the sum of its parts and we focus here on ensuring that Windows Server systems are properly installed and configured.

 Microsoft Server uses Server Manager roles and features to configure and install server components.  To open the server manager goto ->Administrative Tools->Server Manager.
 

Figure 1:  Computer Management Interface, all Windows

Figure 2:  Server Manager for Microsoft Windows Servers

Microsoft Server Manager gives you a good snapshot of the configured features of your server.  You can see firewall settings, registration information, roles installed, and Windows Server features that are installed and enabled.  By default a Windows server installation leaves much of this configuration for post-installation tasks.

You can also use the Programs and Features control panel applet to list installed applications.  In Windows you can use the Task Manager to view running processes, their paths, and system utilization.

Process explorer is a Sysinternal tool now owned and supported by Microsoft.  Process Explorer allows you to see processes and their perspective process trees and dependencies. 

Figure 3:  Sysinternal Process Explorer showing running processes.

To show disk space and utilization and to manage any disk volumes use the Disk Management feature in the Server Manager.

Figure 4: Windows Server Disk Management view in Computer Management application.

To see startup processes there are several places to check.  The msconfig utility is a good place to start.  This application gives you the running and startup services all in one convenient place.
 

Figure 5:  Msconfig application showing services and status.

The windows registry contains many settings and startup options as well.  Using the regedit application you can check the following registry key for tasks that are set to run when windows starts.

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run

Also, the startup program menu is a good place to look for tasks that may run once a user is logged into the system.  Often times malware is started via this startup option out of a users profile directory.  Be sure to check both the All Users startup folder and the startup folder in each user profile directory.

Utilize the Windows update application to configure system updates if you do not have an enterprise patch management system.  From within the Windows Update applet you can set when your system runs updates and reboot behavior.  Many server systems should be manually updated, tested, and restarted during maintenance windows.

Figure 6:  Un-configured Windows updates interface for Legacy Windows Operating Systems

Figure 7: Use gpedit to override Windows 10 and Server settings by Microsoft.  

Ensure that system time is correct and synchronized to a reliable time source

To setup time synchronization use the system clock or the control panel applet for Date and Time.  The Internet Time tab allows you to configure a time source.

Figure 8:  Windows interface for setting time server source

You can also utilize the w32tm command line options to configure the Windows Time Service. If your system is on a Windows Domain, time synchronization is important for local maintenance and system tasks.  Domain computers will sync to your designated domain controllers which should be synchronized to a reliable external time source.  All computer clocks vary slightly and you may notice time drift more on older systems due to low CMOS battery voltage.

To fine tune time synchronization and server settings look at the registry keys under:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\W32Time

From within these registry settings you can edit polling intervals, time sources, and fine tune your time variance and correction behaviors.

Log file maintenance and configuration

Windows log files should be configured properly.  Log files are the first place to look when you suspect odd system behavior.  Properly configured log files should be setup so that they do not overwrite themselves as this is one method that an attacker might cover their tracks.  If possible archive log files and copy them off to another location to prevent log file tampering. 

Various third party log management tools are available, but the build in Windows interface allows easy filtering and management of basic log file tasks.  You can also use the built in subscription and log file collection services to centralize and copy off log files.

Figure 9: Configuration dialog to change the log file path, size, and overwrite settings. Note:  Archive the log file as a minimum.

Lock down file system security, permissions, and Group Policies

Windows utilizes the NTFS file system which allows for granular file permissions based on access control lists.  Server 2012 now includes another layer of access control via Dynamic Access Control technology.  To edit the NTFS permissions and audit settings for files and directories right click the file or directory and goto Properties.  Then under the security tab you can open Advanced Settings to see the following applet.

Figure 10:  NTFS Access Control List for wwwroot directory

Note that in order for file auditing to be enabled and active you have to enable object access success and/or failure in the applicable group policy or local security policy and then enable auditing for the files you want to audit access to through these advanced security settings.

Utilize the Local Security Policy management console or edit the effective domain policy to meet your organizations requirements.  There are many settings within the Local Security Policy and we touch on a couple important ones here.  It is a good idea to look through these settings in detail as you can modify the security behavior in a very granular way depending on your needs.

Password policies should be updated to meet your needs.  Password age of 90 days or less is recommended.  It is also recommended for the system to remember passwords so that users cannot recycle old passwords.  Password length should be over 10 characters and complexity requirements are enabled by default.

Figure 11:  Local Security Policy MMC for password policy settings.

Auditing should also be enabled for success and failure.  There are several things which you can enable auditing for.  At the very least you should enable Success and Failure Auditing for logon events and privileged use.  Events that correspond to these settings are logged in the Windows Security event log.

Figure 12: Configure Auditing for Success and Failure of various events.

Under the User Rights Assignment policy you find several settings that are worth checking.  You can specify which users have the logon locally rights and can deny or allow granularly based on your needs.

Figure 13: Various user rights assignments on the local policy.

There are various command line tools for applying and testing group policy settings. 

The most effective command line tool for seeing the effective audit policy is auditpol.exe.
auditpol.exe /get /category:*

To reapply effective policies to a computer you can wait about 15 minutes, restart the machine, or run gpupdate.exe from the command prompt.

Audited objects and events are logged in the system security event logs.

Figure 14:  Security Event log showing Audited events.

Follow best practices for securing any SQL data and log files.  SQL BINN and DATA file directories should only allow those users access that need it.  You can also utilize the Best Practice Analyzer to verify your installation and security configuration.

Database security has its own chapter however these things are worth considering.  When protecting a database is that data is often times the fields are clear text unencrypted.  In the least protected information that you are storing needs to be encyped data fields.   Password and sensitive data such as credit card numbers should be hashed and the hashed data value should reside in the database. Encryption of the underlying file system and any database backups is recommended. 

User access to database applications should be over SSL connections and clear text authentication should be disabled.  SSL certificate installation and safeguarding helps to prevent man-in-the-middle compromises.  Backups and file systems should be physically safeguarded to prevent attackers from having a crack at the database.  Remember once an attacker has the data or access to the server console your system is as good as hacked with most measures such as encryption and hashing only delaying the disclosure of data.

Web applications should be protected against SQL injection attack methods and all input fields should be filtered and defined.

Configure IIS and verify permissions on website file folders.  When you install and configure IIS, only install the features that you need.  If you are using third party engines like PHP or WordPress be sure to keep these packages up to date with the latest stable release.  Known vulnerabilities in third party apps are often the attack vector used to compromise a system.

IIS includes built in security features that should be enabled and configured such as URL Authorization, Request Filtering, and IP address restrictions.  Request filtering passes all incoming requests through a set of rules that helps to ensure only valid requests are allowed.

The IIS management console allows you to configure these settings and adjust them to meet your needs.

Configuration should take into account your network segmentation and server placement.  Windows Firewall is a robust host based firewall which allows for granular port, protocol, and application configuration.  Only those services that need to be opened should be opened. 

Windows firewall comes pre-loaded with inbound and outbound rules for most services.  You can enable and disable these as a starting point.

Figure 15: Windows Firewall and Advanced security interface.

Please see section on security through obscurity for more settings.

Even though Symantec recently reported that Anti-virus is useless, it is recommended to run anti-virus or anti-malware software on your system.  These applications or only as good as their configuration and current definition versions but can allow you to be protected against known wild variants of bad software.

System files should be checked for integrity and compared regularly to known good source.  You can easily find and compare checksums of system files and backup files.  If configuration files have changed it should raise a red flag. 

Commercial anti-virus software is available for Windows systems and is recommended to have this installed and properly configured.  Some anti-virus software has problems with large database files so you will want to exclude them from scanning if your disk and CPU utilization is a problem.  Automatic updates or at least regular manual updates should be configured for your anti-virus solution.

Windows server makes use of the Security Configuration Wizard (SCW) to help configure your system.  The security configuration wizard can be launched from within the Administrative tools or the server manager tools.

Figure 16:  Windows Security Configuration Welcome screen

This built in Microsoft wizard allows you to create, edit, apply existing or roll back configuration settings.  The wizard asks you questions about your desired configuration and then attempts to make the Security Policy changes and Firewall changes for you based on your needs.

Figure 17: Security Configuration Wizard – create, edit, apply existing, and rollback options

Figure 18:  The SCW Viewer allows you to see at a glance what your settings are

Utilizing the SCW Viewer you can look at your configuration database and the settings which the wizard can control.  Once you find the configuration that is proper for your application you can save these and apply them to other servers in your environment.

Before applying SCW settings you can see the before and after settings on various services and features.

Figure 19:  Print spool service before configuration changes and after

It is important to note that you should understand what the underlying consequences are for changing the settings through this wizard.  A production server should be tested before applying new policies and you should make sure that you get a backup of your settings before you proceed if your system is already in production.

#WannaCry SMB Stack Hardening – Example of hardening to mitigate a security threat on your network.

During the week of Monday May 8th, 2017 a fast spreading malware referred to as WannaCry began to spread around the globe affecting many networks with a ransomeware.  Ransomeware is when a targetted computer is taken over by a program where the data or system is held hostage or in the case of the WannaCry attack is encrypted with a message to pay a ransome in order to restore usability.

The WannaCry malware attacks primarily used a known vulnerability in the Microsoft core Server Mesage Block protocol, or SMBv1.  Microsoft released patches for this particular vulnerability however one way to mitigate this problem and future problems with SMBv1 is to disable this protocol and enable or force SMBv2 and SMBv3.

Using either the registry or the windows power shell you can force your servers to implement this configuration.  The official Microsoft Support site has details on how to perform this for your operating system.  This support site can be found at “https://support.microsoft.com/en-us/help/2696547/how-to-enable-and-disab…“

On Windows 10 or Server 2012 and newer use the following command in powershell to disable SMBv1.

“Set-SmbServerConfiguration -EnableSMB1Protocol $false”

To check which versions of the SMB protocol your system is running, on a Windows 10 desktop or Server 2012 or newer system, you can use powershell command: 

“Get-SmbServerConfiguration | Select EnableSMB1Protocol, EnableSMB2ProtocolGet-SmbServerConfiguration”

A screen shot of output below shows that the SMBv1 protocol is disabled.

In order to enable the SMBv2 and SMBv3 protocols for a Windows 10 desktop or Server 2012 or newer system, you can use powershell command:

 “Set-SmbServerConfiguration -EnableSMB2Protocol $true”

After disabling SMBv1 and Enabling SMBv2 you can then re-run the “Get-SmbServerConfiguration | Select EnableSMB1Protocol, EnableSMB2ProtocolGet-SmbServerConfiguration” command and see similar output to the following screen shot.

Microsoft Security References:

http://technet.microsoft.com

http://support.microsoft.com/kb/2029023

http://technet.microsoft.com/en-us/security

Table of Contents

Analysis, Cyber Security, Management

Harden Linux Servers

Aug 5, 2021 by BITS Media 0 Comments , , , , , , , , , , , , , ,

*There are many distributions of Linux, our guide covers most standard Debian, RedHat, CentOS and BSD versions, however your particular distribution of Linux may use different default paths and system configuration files. 

Operating system installation

The base operating system installation should be healthy with a minimal install.  Your system should only have the software and packages installed that are being used.  Installation for kernel and system devices should be using the most current stable releases available.  Your system and data partitions should have enough space for daily maintenance routines and working data.  Depending on your needs you may need more space or can get by with less space if your server configuration and data growth is static.  Running services and boot processes should be minimal and only what is needed for your server application.  System temp directories and swap memory files should be properly configured for your installation.

To list installed packages follow these command line samples:

RedHat RPM based
->rpm -qa

Debian_based
->dpkg –get-selections

BSD
->pkg_info

To show your kernel version and details
->uname –a

Utilize the ps command to see running process.  You should gather a baseline of running processes as a regular audit of system security.

Show processes for Linux
->ps -e

Show processes on BSD
->ps ax

To show disk space and utilization use the df command
->df -a

To see free memory
->free -m

To see startup processes
->chkconfig  -list

Startup scripts can be found in the following locations

/etc/rc.d/*
/etc/rc.d/rc3.d/ or /etc/rc3.d/
/etc/rc.d/rc5.d/ or /etc/rc5.d/
Startup scripts start with an “S”.

/etc/init.d/*    is where service daemons are configured.
 

Depending on your Linux distribution you have a couple of options for ensuring that your system software is up to date for known vulnerabilities.  The easiest way to update software and dependencies is to use a package manager and trusted distribution update sources.  If you are running third party applications then make sure that you keep those up to date as well.

RedHat based systems use the RedHat Package Manager (RPM).  This package manager uses the up2date command with many options to check for dependencies and version updates.  RedHat and various other distributions that use RPM require registration and/or purchase to subscribe to automatic update services.

The rpm architecture includes several tools to build and install rpm packages.  The rpm database keeps track of software installed on your system which allows you to easily upgrade or uninstall packages.  The following example shows how to build an rpm package and install the apache web server from a source tarball.

->rpmbuild -tb httpd-2.4.x.tar.bz2
The rpmbuild utility will automatically create the rpm packages and will also list the dependencies that your system may be missing.

->rpm -U httpd-2.4.x-1.i686.rpm

Debian based systems utilize the Debian Package Manager.  Various command line utilities are available such as aptitude and apt-get which will source packages from standard Debian installation sources and check for dependencies.

->apt-get update

->apt-get upgrade

->apt-get install
 

Without the use of a package manager you will need to download source files then config and make software packages to update your system manually with a local compiler.

Ensure that system time is correct and synchronized to a reliable time source

Show system date and time
–>date

To setup a time server edit /etc/ntp.conf
Enter a line for each time source as follows

server ntpserver.name.com
Replace “ntpserver.name.com” with a time server or pool address that you choose.

Enable system logging and audit log files

System logging is an important piece to system hardening and security.  Proper configuration and auditing of log files is recommended.  On Linux there are various different log software daemons.  Syslog, syslog-ng and rsyslog are the commonly included logging utilities with Linux distributions. 

Permissions should be set for log files so that root is owner and they are not available to standard users.  Also, you should configure system log files to be sent or copied to a trusted centralized location so that they are tamper resistant.  When attackers breach a system they can cover their tracks or wreak havoc on your log files to make it hard to determine what or how they accessed it.

The configuration files for these logging daemons are located in /etc and the default log file repositories are in /var/log.

/etc/syslog.conf
/etc/rsyslog.conf

There are many commercial and open source software packages for collecting and auditing log files.  Many of these packages allow you to create alerts as well as provide more friendly filters to make viewing less tedious.  Server logs should be checked on a regular basis and can help troubleshoot other system problems. 

Lockdown file system security and permissions

To list file permissions and owner
->ls -l

Utilize the chmod command to set file system permissions.  Ensure that the following files are owned by root with their perspective permissions.

/etc/passwd set to rw-r–r–
/etc/group set to rw-r–r–
/etc/fstab set to -rw-r–r–
/etc/shadow set to r——–

The chmod command is a utility built into the command shell to manage file permissions and ownership.   See man chmod for symbolic and numeric usage options.  Also see http://ss64.com/bash/chmod.html as a good tool for understanding and converting mod permissions on files and directories.

Set cron permissions to allow only root to add cron jobs.
create/etc/cron.allow and /etc/at.allow with root as the owner and permission set to r——–
root should be the only text in these files.

Ensure that password policies meet your organizational requirements.  /etc/login.defs  is used by the system to configure password policies.  See man login.defs for configuration details.  Password aging should be enforced at 90 days or less and minimum length should be set with at least 10 characters.  Highly secure systems should enforce longer passwords.

Utilize sudo rather than su to perform super user tasks

Sudo is a per command super user utility which users can launch with their own passwords.  In other words you are able to keep the root password safe and secret and give administrative users the proper access to run tasks via sudo commands.

Edit /etc/sudoers  files to give users sudo access.  To run a command under the super user context precede commands with sudo.

->sudo pico /etc/ssh/sshd_config
Will open the sshd_config file with the pico editor as super user.

Configure networking, firewall, and port settings

Network segmentation and placement of your server may play a role in how much effort you put into configuring your local firewall settings.  Whether your network is NAT, DMZ, local trusted, or placed directly on a public segment will determine how you need to configure local host-based firewall settings.  Network segmentation and firewall settings used in conjunction with an edge security solution is recommended.

To see which network ports are open and listening run netstat -a

Linux uses INPUT, FORWARD, and OUTPUT chains via iptables for host-based firewall rules.
The iptables rules are simple logic rules to determine whether or not a packet is accepted or rejected.  The order of the rules is important to consider.  Incoming traffic is filtered from top down.

Ubuntu iptables reference is one of the most complete and can be found at
https://help.ubuntu.com/community/IptablesHowTo

To view currently running iptables configuration:
->sudo iptables -L

Sample output from this command on a running system:

Chain INPUT (policy ACCEPT)
target     prot opt source               destination
REJECT      all  —  anywhere             loopback/8          reject-with icmp-port-unreachable
ACCEPT     all  —  anywhere              anywhere            state RELATED,ESTABLISHED
ACCEPT     tcp  —  anywhere             anywhere            tcp dpt:www
ACCEPT     tcp  —  anywhere             anywhere            tcp dpt:https
ACCEPT     tcp  —  anywhere             anywhere            tcp dpt:smtp
ACCEPT     tcp  —  anywhere             anywhere            tcp dpt:pop3
ACCEPT     tcp  —  anywhere             anywhere            tcp dpt:pop3s
ACCEPT     tcp  —  anywhere             anywhere            tcp dpt:imap2
ACCEPT     tcp  —  anywhere             anywhere            tcp dpt:imaps
ACCEPT      all  —  anywhere             anywhere            state RELATED,ESTABLISHED
REJECT      icmp —  anywhere          anywhere            reject-with icmp-port-unreachable
LOG              all  —  anywhere             anywhere            limit: avg 5/min burst 5 LOG level debug prefix `iptables denied: ‘
REJECT      all  —  anywhere              anywhere            reject-with icmp-port-unreachable

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination
REJECT      all  —  anywhere             anywhere            reject-with icmp-port-unreachable

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination
ACCEPT     all  —  anywhere             anywhere

The following iptables configuration file corresponds to the output above which allows HTTP(port 80), HTTPS (443), SMTP (25), outbound connections, pop3, imap,  imaps(993), and pop3s(995).  See security through obscurity section for other tricks.  Packets that meet the filter rules are accepted.  All others are dropped. 

//file = /etc/sysconfig/iptables.sample

# Generated by iptables-save v1.4.8 on Thu Nov 29 07:35:35 2012

*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
[0:0] -A INPUT -d 127.0.0.0/8 ! -i lo -j REJECT –reject-with icmp-port-unreachable
[9855:1333917] -A INPUT -m state –state RELATED,ESTABLISHED -j ACCEPT
[20:964] -A INPUT -p tcp -m tcp –dport 80 -j ACCEPT
[16:832] -A INPUT -p tcp -m tcp –dport 443 -j ACCEPT
[0:0] -A INPUT -p tcp -m tcp –dport 25 -j ACCEPT
[0:0] -A INPUT -p tcp -m tcp –dport 110 -j ACCEPT
[0:0] -A INPUT -p tcp -m tcp –dport 995 -j ACCEPT
[0:0] -A INPUT -p tcp -m tcp –dport 143 -j ACCEPT
[0:0] -A INPUT -p tcp -m tcp –dport 993 -j ACCEPT
[0:0] -A INPUT -m state –state RELATED,ESTABLISHED -j ACCEPT
[535:32144] -A INPUT -p icmp -j REJECT –reject-with icmp-port-unreachable
[921:58908] -A INPUT -m limit –limit 5/min -j LOG –log-prefix “iptables denied: ” –log-level 7
[1067:66503] -A INPUT -j REJECT –reject-with icmp-port-unreachable
[0:0] -A FORWARD -j REJECT –reject-with icmp-port-unreachable
[12195:1597429] -A OUTPUT -j ACCEPT
COMMIT

# Completed on Thu Nov 29 07:35:35 2012

//eof /etc/sysconfig/iptables.sample

You can also use gui tools such as system-config-firewall and system-config-firewall-tui to configure your local host firewall.  Linux distributions allow you to specify basic firewall settings during installation but most default installations are open and allow all traffic.

Be cautious when editing firewall rules on a remote system as you can block yourself out of your own system.  See section on security through obscurity for more settings.

Configure and secure SSH server daemon and Xwindows settings

Remote access should be configured with SSH version 2 and you should not allow root login.  Edit SSH server settings in the /etc/ssh/sshd_config file.  Key settings for the ssh daemon include:

PermitRootLogin  no  – do not allow root to login via ssh, users can still su or sudo once logged in
Protocol 2   – force ssh to use protocol version 2 which is more secure
AllowUser   user1, user2, user4  – tell ssh which users are allowed access
DenyUser   user3, user5   – tell ssh which users are denied access
Port 22  – set the listening port number for ssh daemon, see security by obscurity

If you are configuring and utilizing X windows ensure that you enable X11 forwarding so that sessions are encrypted to your X server via SSH.  Otherwise X windows sessions are unencrypted and easily sniffed off the network.  Enabling X windows should be minimized as there are known exploits and system overhead with it.

 Advanced packet filtering with tcpd and hosts_access control files

Tcpwrappers allow for robust access control and logging of network daemons and was one of the earliest packet filtering methods for Linux systems.  The tcpd daemon can be used in conjunction with inetd, when services are defined to run via inetd.conf, or daemons can be compiled and configured to include the libwrap library natively. 

Access control rules for tcpd are located in /etc/host.allow and /etc/hosts.deny. 

Many options are available to shape and filter incoming connections with these access control rules.  See man hosts_access for good documentation on how to use and implement the access control programming language.  Connections that are filtered by tcpd are logged via standard syslog log file mechanisms so that auditing of these wrapped services is possible.

If your system is running an http daemon there are a couple of basic security precautions that you should take.  Apache web server is a robust web server platform with many commercial and free add-ons to enhance its functionality.  Apache mods (modules) are configurable enhancements to the Apache web server system.  File system security for content directories as well as the executable http binaries and apache installation files should be locked down and checked.  Root should be the owner of these directories and they should not be writable by others.

->ls -l /etc/apache2

-rw-r–r–           1   root   root     8096                 May 31 20:49                 apache2.conf
drwxr-xr-x       2   root   root     1024                 Nov  8  19:05   conf.d
-rw-r–r–           1   root   root              0 Mar 19  13:31 httpd.conf
drwxr-xr-x       2   root   root     9216                 Nov  8  19:05   mods-available
drwxr-xr-x       2   root   root     1024                 Mar 19  13:40 mods-enabled
-rw-r–r–           1   root   root        786 May 31 21:03                 ports.conf
drwxr-xr-x       2   root   root     1024                 Nov  8  19:05   sites-available
drwxr-xr-x       2   root   root     1024 Mar 19  13:30 sites-enabled

The following system settings in your apache config file are recommended to further limit access.

<Directory />
   AllowOverride None
</Directory
//Prevents users from overriding server settings with different .htaccess files.

<Directory />
   Order  Deny, Allow
   Deny from all
</Directory>
//To prevent users from accessing file system directories

<Directory /path/public_html>
  Order  Deny, Allow
  Allow from all
</Directory>
//Allow access to specified web site directory replace path with your path

The Apache mod_security package is recommended to enable enhanced configuration in your Apache configuration files.  Extra logging and more granular control over error messages and file uploads is enabled. 

The Apache HTTP server website provides a good reference.  http://httpd.apache.org/docs/2.2/misc/security_tips.html

Secure and Configure MySQL and Postgress SQL servers

One important thing to consider when protecting a database is that data is often clear text inside the database files.  Encryption of the underlying file system and any database backups is recommended.  Password and sensitive data such as credit card numbers should be hashed and the hashed data value should reside in the database. 

User access to database applications should be over SSL connections and clear text authentication should be disabled.  SSL certificate installation and safeguarding helps to prevent man-in-the-middle compromises.  Backups and file systems should be physically safeguarded to prevent attackers from having a crack at the database.  Remember once an attacker has the data or access to the server console your system is as good as hacked with most measures such as encryption and hashing only delaying the disclosure of data.

Web applications should be protected against SQL injection attack methods and all input fields should be filtered and defined.

It is recommended to run Anti-virus or anti-malware software on your system.  These applications or only as good as their configuration and current definition versions but can allow you to be protected against known wild variants of bad software.

System files should be checked for integrity and compared regularly to a known good source.  You can easily find and compare checksums of system files and backup files.  If configuration files have changed it should raise a red flag.  Intrusion detection systems should be configured to watch these files.

Linux Security References:

http://www.debian.org/security

http://www.rpm.org/max-rpm/ch-rpm-upgrade.html

https://access.redhat.com/security/updates/

http://www.freebsd.org/security/

http://httpd.apache.org/docs/2.2/misc/security_tips.html

https://help.ubuntu.com/community/IptablesHowTo

http://kernel.org

http://ss64.com/bash/chmod.html