IDS/IPS Definition and Classification

Contents Overview of IDS/IPS Components of an IDS/IPS IDS/IPS classification By scope of protection By detection model

Overview of IDS/IPS Intrusion Intrusion detection Intrusion prevention A set of actions aimed at compromising the security goals (confidentiality, integrity, availability of a computing/networking resource) Intrusion detection The process of identifying and responding to intrusion activities Intrusion prevention The process of both detecting intrusion activities and managing responsive actions throughout the network.

Overview of IDS/IPS Intrusion detection system (IDS) A system that performs automatically the process of intrusion detection. Intrusion prevention system (IPS) A system that has an ambition to both detect intrusions and manage responsive actions. Technically, an IPS contains an IDS and combines it with preventive measures (firewall, antivirus, vulnerability assessment) that are often implemented in hardware.

Overview of IDS/IPS Some authors consider an IPS a new (fourth) generation IDS – a convergence of firewall and IDS. IPS use IDS algorithms to monitor and drop/allow traffic based on expert analysis. The ”firewall” part of an IPS can prevent malicious traffic from entering/exiting the network. It can also alert the operator about such activities.

Overview of IDS/IPS A complete IPS solution usually has the capability of enforcing traditional static firewall rules and operator-defined whitelists and blacklists. IPS are very resource intensive. In order to operate with high performance, they should be implemented by means of the best hardware and software technologies. IPS hardware often includes ASICs (Application Specific Integrated Circuits).

Overview of IDS/IPS Principal differences between IDS and IPS: IPS try to block malicious traffic, unlike IDS that just alert personnel to its presence. IPS acts to combine single-point security solutions (anti-virus, anti-spam, firewall, IDS, …).

Overview of IDS/IPS Basic assumptions: System activities are observable Normal and intrusive activities have distinct evidence – the goal of an IDS/IPS is to detect the difference.

Components of an IDS/IPS System activities are observable Incoming traffic/logs Data pre-processor Activity data Detection model(s) Normal and intrusive activities have distinct evidence Detection algorithm Alerts Action/Report Decision criteria Alert filter

Components of an IDS/IPS Data pre-processor Collects and formats the data to be analyzed by the detection algorithm. Detection algorithm Based on the detection model, detects the difference between ”normal” and intrusive audit records. Alert filter Based on the decision criteria and the detected intrusive activities, estimates their severity and alerts the operator/manages responsive activities (usually blocking).

Components of an IDS/IPS Incoming traffic/log data Packets – headers contain routing information, content may (and is more and more) also be important for detecting intrusions. Logs – a chronological set of records of system activity.

Components of an IDS/IPS Incoming traffic/log data (cont.) Problems related to data Inadequate format for intrusion detection Information important for intrusion detection is often missing (e.g. in log files). Thus we need some data pre-processing Adjust data format (relatively easy) Resolve for missing data (not so easy) Insertion of reconstructed values Special distances (for unequal-length data patterns).

Components of an IDS/IPS Detection algorithm Checks the incoming data for presence of anomalous content. A major detection problem There is no sharp limit between “normal” and “intrusive” – it often depends on the context – hence statistical analysis of the input data may be useful. To determine the context, a lot of memory is needed.

Components of an IDS/IPS Alert filter Determines the severity of the detected intrusive activity. A major decision problem It is difficult to estimate the severity of threat in real time. Filtering is normally carried out by means of a set of thresholds (decision criteria). Thresholds should be carefully set in order to maintain a high level of security and a high level of system performance at the same time.

IDS/IPS classification By scope of protection (or by location) Host-based IDS Network-based IDS Application-based IDS Target-based IDS By detection model Misuse detection Anomaly detection

IDS classification Host-based Collect data from sources internal to a computer, usually at the operating system level (various logs etc.) Monitor user activities. Monitor executions of system programs.

IDS classification Network-based Collect network packets. This is usually done by using network devices that are set to the promiscuous mode. (A network device operating in the promiscuous mode captures all network traffic accessible to it, not just that addressed to it.) Have sensors deployed at strategic locations Inspect network traffic Monitor user activities on the network.

IDS classification Application-based Collect data from running applications. The data sources include application event logs and other data stores internal to the application.

IDS classification Target-based (integrity verification) Generate their own data (by adding code to the executable, for example). Use checksums or cryptographic hash functions to detect alterations to system objects and then compare these alterations to a policy. Trace calls to other programs from within the monitored application.

IDS classification Misuse detection Asks the following question about system events: Is this particular activity bad? Misuse detection involves gathering information about indicators of intrusion in a database and then determining whether such indicators can be found in incoming data.

IDS classification Misuse detection (cont.) To perform misuse detection, the following is needed: A good understanding of what constitutes a misuse behaviour (intrusion patterns, or signatures). A reliable record of user activity. A reliable technique for analyzing that record of activity (very often – pattern matching).

Misuse Detection Intrusion patterns (signatures) Analysis (e.g. pattern matching) Intrusion Activities Signature example: if src_ip = dst_ip then “land attack”

IDS classification Misuse detection (cont.) It is best suited for reliably detecting known misuse patterns (by means of signatures). It is not possible to detect previously unknown attacks, or attacks with unknown signature. A single bit of difference may be enough for an IDS to miss the attack. However, it is possible to use the existing knowledge (for instance, of outcomes of attacks) to recognize new forms of old attacks.

IDS classification Misuse detection (cont.) Misuse detection has no knowledge about the intention of activity that matches a signature. Hence it sometimes generates alerts even if the activities are normal (normal activities often closely resemble the suspicious ones). Hence IDS that use signature detection are likely to generate false positives.

IDS classification Misuse detection (cont.) New attacks require new signatures, and the increasing number of vulnerabilities causes that signature databases grow over time. Every packet must be compared to each signature for the IDS to detect intrusions. This can become computationally expensive as the amount of bandwidth increases.

IDS classification Misuse detection (cont.) When the amount of bandwidth overwhelms the capabilities of the IDS, it causes the IDS to miss or drop packets. In this situation, false negatives are possible.

IDS classification Anomaly detection Anomaly detection involves a process of establishing profiles of normal user behaviour, comparing actual user behaviour to those profiles, and alerting if deviations from the normal behaviour are detected. The basis of anomaly detection is the assertion that abnormal behaviour patterns indicate intrusion.

IDS classification Anomaly detection (cont.) Profiles are defined as sets of metrics - measures of particular aspects of user behaviour. Each metric is associated with a threshold or a range of values.

IDS classification Anomaly detection (cont.) Anomaly detection depends on an assumption that users exhibit predictable, consistent patterns of system usage. The approach also accommodates adaptations to changes in user behaviour over time.

IDS classification Anomaly detection (cont.) The completeness of anomaly detection depends on the selected set of metrics – it should be rich enough to express as much of anomalous behaviour as possible. Capable of detecting new attacks.

IDS classification Anomaly detection (cont.) An attacker can replicate a misuse detection system and check which signatures it detects. Then he/she can use the attack not detectable by the IDS in question. This is not possible to do with an anomaly detection system.

IDS classification Anomaly detection (cont.) However, it is not always the case that abnormal behaviour patterns indicate an intrusion – sometimes, rare sequences represent normal behaviour. This is a major problem in anomaly detection – false positives. If anomaly detection IDS thresholds are set too high, we may miss the attacks and have false negatives.

Anomaly Detection Profiles of normal behaviour Intrusion Analysis Activities

IDS classification Anomaly detection (cont.) Methods of anomaly detection: Statistical methods Artificial intelligence (cognitive science,…) Data mining Mathematical abstractions of biological systems (neural nets, immunological system simulation, process homeostasis…) Etc.

IDS classification The fundamental debate between proponents of anomaly detection and proponents of misuse detection: Overlap of the regions representing "normal," and "misuse “ activities.

IDS classification The proponents of anomaly detection assert that the intersection between the two regions is minimal. The proponents of misuse detection assert that the intersection is quite large, to the point that given the difficulties in characterizing "normal” activity, it is pointless to use anomaly detection.

IDS classification The solution of this problem is probably in combining the two detection models. Although the IDS/IPS manufacturers do not publish the details of their designs, it is quite probable that they combine misuse detection and anomaly detection approach in their solutions.

Attack fundamentals Four phases in the attacking process: Planning phase Reconnaissance phase Attack phase Post attack phase.

Attack fundamentals

Attack fundamentals Planning phase Can take many different forms. The attacker often makes use of the system in its intended manner before making the attack. Example: the attacker may sign up for an account on an online e-commerce system or log onto a public server. This type of publicly available legitimate access helps the attacker define the scope and goals of the attack.

Attack fundamentals Planning phase (cont.) After the initial preparation is complete, the attacker decides on the scope of the attack. The attacker may have various goals: Denial of service Escalation of legitimate privileges Unauthorized access Data manipulation The motivation behind an attack often dictates which of these goals are chosen.

Attack fundamentals Reconnaissance phase The attacker next gathers information or performs reconnaissance on the targeted network. The attacker carries out a variety of different inquiries with the goal of pinpointing a specific method of attack (port scanning etc.) The goal of the attacker in this phase is to narrow down the field of thousands of possible exploits to a small number of vulnerabilities that are specific to the targeted host/network.

Attack fundamentals Reconnaissance phase (cont.) The attacker attempts to make this reconnaissance as hard to notice as possible. Even so, there are many different means of reconnaissance and some of them can be detected by an intrusion detection system. Sources of information for the attacker: Legitimate public data (forums, public databases, public monitoring tools, etc.) Vulnerability scanning (ping, TCP connect, OS and version scanning, etc.)

Attack fundamentals Attack phase The traffic generated from attacks can take many different forms. Types of attacks: Denial of service Remote exploits Trojans and backdoor programs Misuse of legitimate access

Attack fundamentals Attack phase (cont.) Denial of service (DoS) Any attack that disrupts the function of a system so that legitimate users can no longer access it. Possible on most network equipment: routers, servers, firewalls, remote access machines, etc. Can be specific to a service (e.g. FTP attack), or an entire machine. Categories of DoS Resource depletion Malicious packet attacks.

Attack fundamentals Attack phase (cont.) Denial of service (DoS) (cont.) Resource depletion DoS attack Functions by flooding a service with so much normal traffic that legitimate users cannot access the service. An attacker inundating a service with normal traffic can exhaust finite resources such as bandwidth, memory and processor cycles. Examples: SYN flood, Smurf, etc.

Attack fundamentals Attack phase (cont.) Denial of service (DoS) (cont.) Malicious packet DoS attacks Function by sending abnormal traffic to a host to cause the service or the host itself to crash. Occur when software is not properly coded to handle abnormal or unusual traffic. Such traffic can cause software to react unexpectedly and crash. Attackers can use these attacks to bring down even IDS. Examples: Microsoft FTP DoS, SNORT ICMP DoS, etc.

Attack fundamentals Attack phase (cont.) Denial of service (DoS) (cont.) Malicious packet DoS attacks (cont.) In addition to unusual traffic, malicious packets can contain payloads that cause a system to crash. A packet's payload is taken as input into a service. If this input is not properly checked, the application can be brought down.

Attack fundamentals Attack phase (cont.) Denial of service (DoS) (cont.) DoS attacks commonly utilize spoofed IP addresses because the attack is successful even if the response is misdirected. The attacker requires no response, and in cases like the Smurf attack, wants at all costs to avoid a response. This can make DoS attacks difficult to defend from, and even more difficult to detect.

Attack fundamentals Attack phase (cont.) Remote exploits Attacks designed to take advantage of improperly coded software to compromise and take control of a vulnerable host. Can function in the same manner as the malicious payload traffic DoS attacks. Take advantage of improperly checked input or configuration errors. Examples: buffer overflow, Unicode exploit, Cookie poisoning, SQL injection, etc.

Attack fundamentals Attack phase (cont.) Trojans and Backdoor programs By installing a backdoor program or a Trojan, an attacker can bypass normal security controls and gain privileged unauthorized access to a host. A backdoor program can be deployed on a system in a variety of different ways. E.g. a malicious software engineer can add a backdoor program into legitimate software code. Backdoor programs might be added for legitimate maintenance reasons in the software development life cycle, but later forgotten.

Attack fundamentals Attack phase (cont.) Trojans and Backdoor programs (cont.) A Trojan is defined as software that is disguised as a benign application. Remote control Trojans typically listen on a port like a genuine application. Through this open port, an attacker controls them remotely. Trojans can be used to perform any number of functions on the host.

Attack fundamentals Attack phase (cont.) Trojans and Backdoor programs (cont.) Some Trojans include portscanning and DoS features. Others can take screen and Webcam captures and send them back to the attacker. Trojans and backdoor programs have traditionally listened on a TCP or UDP port, making it easy to detect them and undertake countermeasures.

Attack fundamentals Attacks phase (cont.) Trojans and Backdoor programs (cont.) Because of that, Trojans have evolved so they no longer need to listen on a TCP or UDP port. Instead, they listen for a specific sequence of events before processing commands. It may be a combination of predetermined source addresses, TCP header information, or false destination ports that do not match to a listening service.

Attack fundamentals Attack phase (cont.) Misuse of Legitimate Access Attackers often attempt to gain unauthorized use of legitimate accounts by getting authentication information. This can be performed by means of technical and/or social engineering methods. IDS, especially the anomaly detection ones, may be used to detect such activities.

Attack fundamentals Post-attack phase After an attacker has successfully penetrated into a host on the targeted network, further actions he/she will take are in general unpredictable. In this phase, the attacker carries out his/her plan and makes use of information resources as he/she considers appropriate.

Attack fundamentals Post-attack phase Possible post-attack activities: Covering tracks Penetrating deeper into network infrastructure Using the host to attack other networks Gathering, manipulating, or destroying data Handing over the host to a friend or a hacker group Walking or running away without doing anything.