Intrusion detection system

An Intrusion Detection System (IDS) is a monitoring system that detects suspicious activities and generates alerts when they are detected. Based upon these alerts, a security operations center (SOC) analyst or incident responder can investigate the issue and take the appropriate actions to remediate the threat.

Classification of Intrusion Detection Systems

Intrusion detection systems are designed to be deployed in different environments. And like many cybersecurity solutions, an IDS can either be host-based or network-based.

• Host-Based IDS (HIDS): A host-based IDS is deployed on a particular endpoint and designed to protect it against internal and external threats. Such an IDS may have the ability to monitor network traffic to and from the machine, observe running processes, and inspect the system’s logs. A host-based IDS’s visibility is limited to its host machine, decreasing the available context for decision-making, but has deep visibility into the host computer’s internals.
• Network-Based IDS (NIDS): A network-based IDS solution is designed to monitor an entire protected network. It has visibility into all traffic flowing through the network and makes determinations based upon packet metadata and contents. This wider viewpoint provides more context and the ability to detect widespread threats; however, these systems lack visibility into the internals of the endpoints that they protect.

Due to the different levels of visibility, deploying a HIDS or NIDS in isolation provides incomplete protection to an organization’s system. A unified threat management solution, which integrates multiple technologies in one system, can provide more comprehensive security.

Detection Method of IDS Deployment

Beyond their deployment location, IDS solutions also differ in how they identify potential intrusions:

• Signature Detection: Signature-based IDS solutions use fingerprints of known threats to identify them. Once malware or other malicious content has been identified, a signature is generated and added to the list used by the IDS solution to test incoming content. This enables an IDS to achieve a high threat detection rate with no false positives because all alerts are generated based upon detection of known-malicious content. However, a signature-based IDS is limited to detecting known threats and is blind to zero-day vulnerabilities.
• Anomaly Detection: Anomaly-based IDS solutions build a model of the “normal” behavior of the protected system. All future behavior is compared to this model, and any anomalies are labeled as potential threats and generate alerts. While this approach can detect novel or zero-day threats, the difficulty of building an accurate model of “normal” behavior means that these systems must balance false positives (incorrect alerts) with false negatives (missed detections).
• Hybrid Detection: A hybrid IDS uses both signature-based and anomaly-based detection. This enables it to detect more potential attacks with a lower error rate than using either system in isolation.

IDS vs Firewalls

Intrusion Detection Systems and firewalls are both cybersecurity solutions that can be deployed to protect an endpoint or network. However, they differ significantly in their purposes.

An IDS is a passive monitoring device that detects potential threats and generates alerts, enabling security operations center (SOC) analysts or incident responders to investigate and respond to the potential incident. An IDS provides no actual protection to the endpoint or network. A firewall, on the other hand, is designed to act as a protective system. It performs analysis of the metadata of network packets and allows or blocks traffic based upon predefined rules. This creates a boundary over which certain types of traffic or protocols cannot pass.

Since a firewall is an active protective device, it is more like an Intrusion Prevention System (IPS) than an IDS. An IPS is like an IDS but actively blocks identified threats instead of simply raising an alert. This complements the functionality of a firewall, and many next-generation firewalls (NGFWs) have integrated IDS/IPS functionality. This enables them to both enforce the predefined filtering rules (firewalls) and detect and respond to more sophisticated cyber threats (IDS/IPS). Learn more about the IPS vs IDS debate here.

Selecting an IDS Solution

An IDS is a valuable component of any organization’s cybersecurity deployment. A simple firewall provides the foundation for network security, but many advanced threats can slip past it. An IDS adds an additional line of defense, making it more difficult for an attacker to gain access to an organization’s network undetected.

When selecting an IDS solution, it is important to carefully consider the deployment scenario. In some cases, an IDS may be the best choice for the job, while, in others, the integrated protection of an IPS may be a better option. Using a NGFW that has built-in IDS/IPS functionality provides an integrated solution, simplifying threat detection and security management.

Books on Intrusion Detection System