Securing Sun Linux Systems: Part I, Local Access and File Systems
This article is the first part of a two-part series that provides recommendations for securing the Sun™ Linux 5.0 operating system. This part provides recommendations for securing local access and file systems. Part II provides recommendations for securing network access and services. The information in this article applies only to the Sun Linux 5.0 distribution, although some techniques or recommendations might apply to other Linux distributions.
It is important to address security for local access and file systems. Often, administrators are solely concerned with protecting a system from remote threats. We recommend that you have equal concern for local, authorized users who can exercise a weak configuration, either inadvertently or maliciously, and gain unauthorized privileges on a system. We highly recommend a layered approach to security where protection is implemented for both local and remote threats, resulting in a more robust security configuration.
Sun Linux 5.0 is based on the Red Hat 7.2 Linux distribution and is a flexible, general purpose operating system. To secure a Sun Linux system against unauthorized access and modification requires changes to its default configuration. Although these changes are in most cases relatively minor, we strongly recommend that you make these changes to improve the security posture of a system. The changes and recommendations in both articles address the majority of methods that intruders use to gain unauthorized or privileged access to Sun Linux systems. You should implement these changes immediately after system installation.
As with most security strategies, you must achieve a balance between system manageability and security. Some recommendations in this article might not apply to your environment and might negatively impact your ability to manage a system. You must know your system and security requirements before starting. Implementing the changes recommended in this article requires planning, testing, and documentation.
This article contains the following topics:
- "Installing and Patching"
- "Minimizing the Installation"
- "Disabling System Services"
- "Verifying Integrity"
- "Securing the Console and Front Panel"
- "Configuring the File System"
- "Managing Accounts"
- "Monitoring System Activity"
- "References and Related Resources"
- "About the Authors"
- "Ordering Sun Documents"
- "Accessing Sun Documentation Online"
Installing and Patching
Since the initial release of the Sun Linux 5.0 operating system, Sun has released several updates and patches. These updates typically include security improvements as well as enhancements related to reliability, performance, and manageability. When building a Sun Linux system, be sure to use the latest software updates and patches to take advantage of these improvements.
We strongly recommend that you apply all security patches to a system immediately after installing it.
Install the System Securely
To prevent attackers from modifying a system or creating backdoors, do not attach the system to a public network until you have installed security patches and completed security modifications. Attackers do not need much time to exploit an unpatched out-of-the-box system.
The Sun Linux software distribution automates nearly every facet of the installation process. This benefit makes each installation repeatable and less prone to error. A side effect of this process is that you cannot select packages or clusters for installation or removal. However, after the installation is completed, you can manually add or remove packages.
Immediately after installing a Sun Linux system, update it with all of the available security patches to help prevent the exploit of known attacks. You can download the software updates and security patches for Sun Linux even if you do not have a service contract.
To identify which version of Sun Linux your system has, enter the following command.
# cat /etc/sun-release
Security patches are available in two forms:
Product Updates Download these from http://sunsolve.sun.com/patches/linux. These updates are clusters of patches that address issues related to reliability, availability, security, and system management. These updates are typically downloaded and installed as a complete group.
Individual Security Patches Download these from http://sunsolve.sun.com/patches/linux/security.html. These patches address security issues in a product, tool, or function. You can download these patches in either the Red Hat package management (RPM) or Source RPM (SRPM) format. SRPMs are RPM files that contain the source code for a program instead of its compiled code (stored in the RPM). In addition, an MD5 signature is on the site for each patch, so that you can verify the integrity of downloaded files. We recommend this step to ensure that patches applied are only those provided by Sun.
Apply only patches that are developed and released by Sun Microsystems, Inc. Although the distribution is based on the Red Hat Linux distribution, patches released by Red Hat should never be applied. Doing so might render the system unsupportable by Sun.
To verify that a patch was applied, use the rpm command. For example, to verify that the xinetd-2.3.7-4.7x.i386.rpm package, available from the security patch web site, is installed, use the following command.
# rpm -q -a | grep xinetd xinetd-2.3.7-4.7x
If the rpm command does not return a match with the correct version, then download the patch from Sun, and install it on the system as soon as possible. If the command returns no value, then the related software package is not installed on the system and, therefore, the patch is unnecessary.
In addition to the Sun Linux security web site, Sun offers a security bulletin mailing list. This list is for administrators who want to receive security bulletins directly from the Sun Security Coordination Team. For more information on joining this list, email the Sun Security Coordination Team or submit a security alert to the following Web site:
Receiving and acting upon these notifications in a timely manner is essential to sustaining a strong security posture.
At this time, Sun does not provide an automated mechanism to ensure that a system is currently using the most recent patches, security or otherwise. This process must be done manually to ensure that all available and applicable patches are installed.
You can use the Sun Cobalt Control Station to monitor and manage large deployments of Sun LX50 systems. For example, you can use it to apply software updates. Using this product might help simplify the patch management process for these sites. For more information, refer to http://www.sun.com/hardware/serverappliances/controlstation.
As with any changes made to a system's configuration, always review the impact of the resulting changes to ensure that the security posture of a system is not diminished. Ensure that previously disabled services remain disabled after patches are applied. In addition, if possible, apply patches to non-production systems first to identify the impact of the changes before implementing them on production systems.