CISSP (ISC)2 Certified Information Systems Security Professional Official Study Guide - Gibson Darril

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process. Instead, security must be continually maintained and reaffirmed. In fact, repeating the risk assessment and analysis process is a mechanism to assess the completeness and effectiveness of the security program over time. Additionally, it helps locate deficiencies and areas where change has occurred. Because security changes over time, reassessing on a periodic basis is essential to maintaining reasonable security.

Countermeasure Selection and Assessment

      Selecting a countermeasure within the realm of risk management relies heavily on the cost/benefit analysis results. However, you should consider several other factors when assessing the value or pertinence of a security control:

      ■ The cost of the countermeasure should be less than the value of the asset.

      ■ The cost of the countermeasure should be less than the benefit of the countermeasure.

      ■ The result of the applied countermeasure should make the cost of an attack greater for the perpetrator than the derived benefit from an attack.

      ■ The countermeasure should provide a solution to a real and identified problem. (Don’t install countermeasures just because they are available, are advertised, or sound cool.)

      ■ The benefit of the countermeasure should not be dependent on its secrecy. This means that “security through obscurity” is not a viable countermeasure and that any viable countermeasure can withstand public disclosure and scrutiny.

      ■ The benefit of the countermeasure should be testable and verifiable.

      ■ The countermeasure should provide consistent and uniform protection across all users, systems, protocols, and so on.

      ■ The countermeasure should have few or no dependencies to reduce cascade failures.

      ■ The countermeasure should require minimal human intervention after initial deployment and configuration.

      ■ The countermeasure should be tamperproof.

      ■ The countermeasure should have overrides accessible to privileged operators only.

      ■ The countermeasure should provide fail-safe and/or fail-secure options.

      Keep in mind that security should be designed to support and enable business tasks and functions. Thus countermeasures and safeguards need to be evaluated in the context of a business task.

Implementation

Security controls, countermeasures, and safeguards can be implemented administratively, logically/technically, or physically. These three categories of security mechanisms should be implemented in a defense-in-depth manner in order to provide maximum benefit (Figure 2.6).

Figure 2.6 The categories of security controls in a defense-in-depth implementation

      Technical

      Technical or logical access involves the hardware or software mechanisms used to manage access and to provide protection for resources and systems. As the name implies, it uses technology. Examples of logical or technical access controls include authentication methods (such as usernames, passwords, smartcards, and biometrics), encryption, constrained interfaces, access control lists, protocols, firewalls, routers, intrusion detection systems (IDSs), and clipping levels.

      Administrative

      Administrative access controls are the policies and procedures defined by an organization’s security policy and other regulations or requirements. They are sometimes referred to as management controls. These controls focus on personnel and business practices. Examples of administrative access controls include policies, procedures, hiring practices, background checks, data classifications and labeling, security awareness and training efforts, vacation history, reports and reviews, work supervision, personnel controls, and testing.

      Physical

      Physical access controls are items you can physically touch. They include physical mechanisms deployed to prevent, monitor, or detect direct contact with systems or areas within a facility. Examples of physical access controls include guards, fences, motion detectors, locked doors, sealed windows, lights, cable protection, laptop locks, badges, swipe cards, guard dogs, video cameras, mantraps, and alarms.

Types of Controls

      The term access control refers to a broad range of controls that perform such tasks as ensuring that only authorized users can log on and preventing unauthorized users from gaining access to resources. Controls mitigate a wide variety of information security risks.

      Whenever possible, you want to prevent any type of security problem or incident. Of course, this isn’t always possible, and unwanted events occur. When they do, you want to detect the events as soon as possible. And once you detect an event, you want to correct it.

      As you read the control descriptions, notice that some are listed as examples of more than one access-control type. For example, a fence (or perimeter-defining device) placed around a building can be a preventive control (physically barring someone from gaining access to a building compound) and/or a deterrent control (discouraging someone from trying to gain access).

      Deterrent

      A deterrent access control is deployed to discourage violation of security policies. Deterrent and preventive controls are similar, but deterrent controls often depend on individuals deciding not to take an unwanted action. In contrast, a preventive control actually blocks the action. Some examples include policies, security-awareness training, locks, fences, security badges, guards, mantraps, and security cameras.

      Preventive

      A preventive access control is deployed to thwart or stop unwanted or unauthorized activity from occurring. Examples of preventive access controls include fences, locks, biometrics, mantraps, lighting, alarm systems, separation of duties, job rotation, data classification, penetration testing, access-control methods, encryption, auditing, presence of security cameras or CCTV, smartcards, callback procedures, security policies, security-awareness training, antivirus software, firewalls, and intrusion prevention systems (IPSs).

      Detective

      A detective access control is deployed to discover or detect unwanted or unauthorized activity. Detective controls operate after the fact and can discover the activity only after it has occurred. Examples of detective access controls include security guards, motion detectors, recording and reviewing of events captured by security cameras or CCTV, job rotation, mandatory vacations, audit trails, honeypots or honeynets, IDSs, violation reports, supervision and reviews of users, and incident investigations.

      Compensating

      A compensation access control is deployed to provide various options to other existing controls to aid in enforcement and support of security policies. They can be any controls used in addition to, or in place of, another control. For example, an organizational policy may dictate that all PII must be encrypted. A review discovers that a preventive control is encrypting all PII data in databases, but PII transferred over the network is sent in cleartext. A compensation control can be added to protect the data in transit.

      Corrective

      A corrective access control modifies the environment to return systems to normal after an unwanted or unauthorized activity has occurred. It attempts to correct any problems that occurred as a result of a security incident. Corrective controls can be simple, such as terminating malicious activity or rebooting a system. They also include antivirus solutions that can remove or quarantine a virus, backup and restore plans to ensure that lost data can be restored, and active IDs that can modify the environment to stop an attack in progress. The access control is deployed to repair or restore resources, functions, and capabilities after a violation of security policies.

      Recovery

      Recovery controls are an extension of corrective controls but have more advanced or complex abilities. Examples of recovery access controls include backups and restores, fault-tolerant drive systems, system imaging, server clustering, antivirus

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