Intrusion detection is the process of monitoring the events occurring in a computer system or network and analyzing them for signs of possible incidents, which are violations or imminent threats of violation of computer security policies, acceptable use policies, or standard security practices.
Intrusion prevention is the process of performing intrusion detection and attempting to stop detected possible incidents. Intrusion detection and prevention systems (IDPS)1 are primarily focused on identifying possible incidents, logging information about them, attempting to stop them, and reporting them to security administrators.
In addition, organizations use IDPSs for other purposes, such as identifying problems with security policies, documenting existing threats, and deterring individuals from violating security policies. IDPSs have become a necessary addition to the security infrastructure of nearly every organization.
IDPSs typically record information related to observed events, notify security administrators of important observed events, and produce reports. Many IDPSs can also respond to a detected threat by attempting to prevent it from succeeding. They use several response techniques, which involve the IDPS stopping the attack itself, changing the security environment (e.g., reconfiguring a firewall), or changing the attack’s content.
This publication describes the characteristics of IDPS technologies and provides recommendations for designing, implementing, configuring, securing, monitoring, and maintaining them. The types of IDPS technologies are differentiated primarily by the types of events that they monitor and the ways in which they are deployed.
This publication discusses the following four types of IDPS technologies:
- Network-Based, which monitors network traffic for particular network segments or devices and analyzes the network and application protocol activity to identify suspicious activity
- Wireless, which monitors wireless network traffic and analyzes it to identify suspicious activity involving the wireless networking protocols themselves
- Network Behavior Analysis (NBA), which examines network traffic to identify threats that generate unusual traffic flows, such as denial of service (DoS) attacks, certain forms of malware, and policy violations (e.g., a client system providing network services to other systems)
- Host-Based, which monitors the characteristics of a single host and the events occurring within that host for suspicious activity.
Implementing the following recommendations should facilitate more efficient and effective intrusion detection and prevention system use for Federal departments and agencies. Organizations should ensure that all IDPS components are secured appropriately.
Securing IDPS components is very important because IDPSs are often targeted by attackers who want to prevent the IDPSs from detecting attacks or want to gain access to sensitive information in the IDPSs, such as host configurations and known vulnerabilities. IDPSs are composed of several types of components, including sensors or agents, management servers, database servers, user and administrator consoles, and management networks.
All components’ operating systems and applications should be kept fully up-to-date, and all software-based IDPS components should be hardened against threats. Specific protective actions of particular importance include creating separate accounts for each IDPS user and administrator, restricting network access to IDPS components, and ensuring that IDPS management communications are protected appropriately, such as encrypting them or transmitting them over a physically or logically separate network.
Administrators should maintain the security of the IDPS components on an ongoing basis, including verifying that the components are functioning as desired, monitoring the components for security issues, performing regular vulnerability assessments, responding appropriately to vulnerabilities in the IDPS components, and testing and deploying IDPS updates. Administrators should also back up configuration settings periodically and before applying updates to ensure that existing settings are not inadvertently lost.
Organizations should consider using multiple types of IDPS technologies to achieve more comprehensive and accurate detection and prevention of malicious activity.
The four primary types of IDPS technologies—network-based, wireless, NBA, and host-based—each offer fundamentally different information gathering, logging, detection, and prevention capabilities. Each technology type offers benefits over the others, such as detecting some events that the others cannot and detecting some events with significantly greater accuracy than the other technologies. In many environments, a robust IDPS solution cannot be achieved without using multiple types of IDPS technologies. For most environments, a combination of network-based and host-based IDPS technologies is needed for an effective IDPS solution.
Wireless IDPS technologies may also be needed if the organization determines that its wireless networks need additional monitoring or if the organization wants to ensure that rogue wireless networks are not in use in the organization’s facilities. NBA technologies can also be deployed if organizations desire additional detection capabilities for denial of service attacks, worms, and other threats that NBAs are particularly well-suited to detecting. Organizations should consider the different capabilities of each technology type along with other cost-benefit information when selecting IDPS technologies.
Organizations planning to use multiple types of IDPS technologies or multiple products of the same IDPS technology type should consider whether or not the IDPSs should be integrated.
Direct IDPS integration most often occurs when an organization uses multiple IDPS products from a single vendor, by having a single console that can be used to manage and monitor the multiple products. Some products can also mutually share data, which can speed the analysis process and help users to better prioritize threats. A more limited form of direct IDPS integration is having one IDPS product provide data for another IDPS product (but no data sharing in the opposite direction).
Indirect IDPS integration is usually performed with security information and event management (SIEM) software, which is designed to import information from various security-related logs and correlate events among them. SIEM software complements IDPS technologies in several ways, including correlating events logged by different technologies, displaying data from many event sources, and providing supporting information from other sources to help users verify the accuracy of IDPS alerts.
Before evaluating IDPS products, organizations should define the requirements that the products should meet.
Evaluators need to understand the characteristics of the organization’s system and network environments, so that a compatible IDPS can be selected that can monitor the events of interest on the systems and/or networks. Evaluators should articulate the goals and objectives they wish to attain by using an IDPS, such as stopping common attacks, identifying misconfigured wireless network devices, and detecting misuse of the organization’s system and network resources.
Evaluators should also review their existing security policies, which serve as a specification for many of the features that the IDPS products need to provide. In addition, evaluators should understand whether or not the organization is subject to oversight or review by another organization. If so, they should determine if that oversight authority requires IDPSs or other specific system security resources. Resource constraints should also be taken into consideration by evaluators.
Evaluators also need to define specialized sets of requirements for the following:
- Security capabilities, including information gathering, logging, detection, and prevention
- Performance, including maximum capacity and performance features
- Management, including design and implementation (e.g., reliability, interoperability, scalability, product security), operation and maintenance (including software updates), and training, documentation, and technical support
- Life cycle costs, both initial and maintenance costs.
When evaluating IDPS products, organizations should consider using a combination of several sources of data on the products’ characteristics and capabilities.
Common product data sources include test lab or real-world product testing, vendor-provided information, third-party product reviews, and previous IDPS experience from individuals within the organization and trusted individuals at other organizations.
When using data from other parties, organizations should consider the fidelity of the data because it is often presented without an explanation of how it was generated. There are several major challenges in performing in-depth hands-on IDPS testing, such as the considerable resources needed and the lack of a standard test methodology and test suites, which often make it infeasible. However, limited IDPS testing is helpful for evaluating security requirements, performance, and operation and maintenance capabilities.
The National Institute of Standards and Technology (NIST) is asking for comments on the updated guidelines. Comments should be sent to firstname.lastname@example.org by August 31.
The NIST Guide to Intrusion Detection and Prevention Systems can be downloaded here: