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As the Internet and other international and national information infrastructures become larger, more complex, and more interdependent, the frequency and severity of unauthorized intrusions into systems connected to these networks are increasing. Therefore, to the extent possible and practical, it is critical to secure the networked systems of an organization that are connected to public networks.
The CERT© Guide to System and Network Security Practices is a practical, stepwise approach to protecting systems and networks against malicious and inadvertent compromise. The practices are primarily written for mid level system and network administrators--the people whose day-to-day activities include installation, configuration, operation, and maintenance of systems and networks. The practices offer easy-to-implement guidance that enables administrators to protect and securely operate the systems, networks, hardware, software, and data that comprise their information technology infrastructure. Managers of administrators are intended as a secondary audience; many practices cannot be implemented without active management involvement and sponsorship.
CERT security practices address critical and pervasive security problems. Practice topic selection is based on CERT's extensive data on security breaches (21,756 in 2000) and vulnerabilities (774 in 2000), that provide a field of vision not available to other security groups. Our practices fill the gap left by the usual point solutions (typically operating-system-specific) or general advice that lacks "how to" details. With CERT security practices, an administrator can act now to improve the security of networked systems.
By implementing these security practices, an administrator will incorporate solutions and protection mechanisms for 75-80 percent of the security incidents reported to CERT. Each practice is written as a series of technology-neutral "how to" instructions, so they can be applied to many operating systems and platforms. However, an administrator can only implement a solution using a specific host operating system. Therefore, we have included examples of technology-specific implementation details in a separate appendix as these tend to become outdated much sooner than the technology-neutral practices.
Throughout the book, emphasis is placed on planning as a precursor to implementing, wherever possible. Ideally, the following risk analysis activities need to occur before deciding what actions to take to improve security:
- Identify and assign value to information and computing assets
- Prioritize assets
- Determine asset vulnerability to threats and the potential for damage
- Prioritize the impact of threats
- Select cost-effective safeguards including security measures
In our observation and as reflected in this book, system and network security is an ongoing, cyclical, iterative process of planning, hardening, preparing, detecting, responding, and improving, requiring diligence on the part of responsible administrators. Configuring and operating systems securely at one point in time do not necessarily mean that these same systems will be secure in the future. And no level of security can ensure 100% protection other than disconnecting from public networks and, even then, the threat of attack from insiders still exists.
To get the most out of this book, you should already know how to install and administer popular operating systems and applications, and be familiar with fundamental system security concepts such as establishing secure configurations, system and network monitoring, authentication, access control, and integrity checking.
The book is organized into two parts and two appendices:
Part I: Hardening and Securing the System. Preventing security problems in the first place is preferable to dealing with them after the fact. This part of the book covers the practices and policies that should be in place to secure a system's configuration. Guidelines for securing general purpose network servers and workstations are contained in Chapter 2, followed by chapters containing additional guidance on securing public web servers and deploying firewalls.
Part II: Intrusion Detection and Response. Even the most secure network perimeter and system configurations cannot protect against every conceivable security threat. Administrators must be able to anticipate, detect, respond to, and recover from intrusions, and understand how to improve security by implementing lessons learned from previous attacks. This part of the book covers practices required to do so.
Appendix A: Security Implementations. The Appendix contains examples of several procedural and tool-based implementations that provide technology-specific guidance for one or more practices (the applicable implementations are referenced in the practices they support). The implementations chosen for this book are specifically geared for Sun Solaris (UNIX) operating environments, given CERT experience. These implementation examples are intended to be illustrative in nature and do not necessarily reflect the most up-to-date operating system versions. The most current versions of over seventy UNIX and Windows NT implementations and tech tips are available on the CERT web site.
Appendix B: Policy Considerations. This Appendix contains all of the security policy considerations and guidance that are presented throughout the book. Having this material in one location may aid you in reviewing and selecting policy topics and generating policy language. You can also treat this Appendix, along with the checklists appearing at the end of each Chapter, as an overall summary of the entire book.
The most effective way to use this book is as a reference. We do not intend that you read it from cover to cover, but rather than you review the introductory sections of each Part and Chapter and then refer to those Chapters and practices that are of most interest.
The web site addresses (URLs) used in this book are accurate as of the publication date. In addition, we have created a CERT web site that contains all URLs referenced in the book. We plan to keep these URLs up to date, provide book errata, and add new references after book publication. At this book site (http://www.cert.org/security-improvement/practicesbk.html), you will find links to all references, information sources, tools, publications, articles, and reports for which a URL exists and is mentioned in the book. We also regularly refer to CERT advisories, incident notes, vulnerability notes, technical tips, and reports, all of which can be found at the CERT web site, http://www.cert.org. We sometimes use the phrase "the CERT web site" to refer to this URL.
The content in The CERT© Guide to System and Network Security Practices derives from Carnegie-Mellon University's Software Engineering Institute (SEI) and CERT Coordination Center. CERT/CC, established in 1988, is the oldest computer security response group in existence. The Center provides technical assistance and advice to sites on the Internet that have experienced a security compromise and establishes tools and techniques that enable typical users and administrators to effectively protect systems from damage caused by intruders. The Software Engineering Institute is a federally funded research and development center with a broad charter to improve the practice of software engineering.
The material that serves as the primary content for this Guide has been posted and updated on the CERT web site over
