Intrusion Detection Systems

1. Intrusion Detection Systems

2. Intrusion Detection Systems • Presently there is much interest in systems, which can detect intrusions, IDS (Intrusion Detection System). • IDS are of very different character. • Some focus on one machine and try to stop the intruder from doing damage, such is LIDS for Linux. • Some can detect a worm attack from the way it spreads from machine to machine, like GrIDS. Tecniche di Sicurezza dei Sistemi

3. Intrusion Detection Systems • Several are actually data mining, they determine from logfiles if there is an intrusion based on reasoning by an expert system, NSTAT is an example. • Many IDS implementations are listening passively to some LAN segment, look at the traffic and detect an intrusion. Snort IDS is a popular freeware program of this Network IDS-type. • Other IDS solutions protect one machine by access controls. Tecniche di Sicurezza dei Sistemi

4. What is Intrusion Detection • Intrusion detection systems (IDSs) are designed for • detecting, blocking and reporting unauthorizedactivity incomputer networks. • “The life expectancy of a default installation of Linux Red Hat 6.2 server is estimated to be less than 72 hours.” • “The fastest compromise happened in 15 minutes (including scanning, probing and attacking)” • “Netbios scans affecting Windows computers were executed with the average of 17 per day” • (source: Honeynet Project) Tecniche di Sicurezza dei Sistemi

5. Motivation for Intrusion Detection Unauthorized Use of Computer Systems Within Last12 Months (source CSI/FBI Study) Tecniche di Sicurezza dei Sistemi

6. Motivation for Intrusion Detection Most Common Attacks (source CSI/FBI) In year 2002 most common attacks were: • Virus (78%) • Insider Abuse of Net Access (78%) • Laptop theft (55%) • Denial of Service and System Penetration (40%) • Unauthorized Access by Insiders (38%) (Red color shows the attack types, which IDS can decrease) Tecniche di Sicurezza dei Sistemi

7. Definitions • Intrusion • A set of actions aimed to compromise the security goals, namely • Integrity, confidentiality, or availability, of a computing and networking resource • Intrusion detection • The process of identifying and responding to intrusion activities Tecniche di Sicurezza dei Sistemi

8. React/ Survive Prevent Detect Why Is Intrusion Detection Necessary? Security principles: layered mechanisms Tecniche di Sicurezza dei Sistemi

9. Elements of Intrusion Detection • Primary assumptions: • System activities are observable • Normal and intrusive activities have distinct evidence • Components of intrusion detection systems: • From an algorithmic perspective: • Features - capture intrusion evidences • Models - piece evidences together • From a system architecture perspective: • Audit data processor, knowledge base, decision engine, alarm generation and responses Tecniche di Sicurezza dei Sistemi

10. Audit Records Audit Data Preprocessor Activity Data Detection Models Detection Engine Alarms Action/Report Decision Engine Decision Table Components of Intrusion Detection System system activities are observable normal and intrusive activities have distinct evidence Tecniche di Sicurezza dei Sistemi

11. Different Types of IDSs 1. Application based;2. Host based; 3. Network based. Tecniche di Sicurezza dei Sistemi

12. Different Types of IDSs Application IDS • Watch application logs • Watch user actions • Stop attacks targeted against an application • Advantages • Encrypted data can be read • Problems • Positioned too high in the attack chain (the attacks reach the application) Tecniche di Sicurezza dei Sistemi

13. Different Types of IDSs Host IDS • Watch kernel operations • Watch network interface • Stop illegal system operations • Drop attack packets at network driver • Advantages • Encrypted data can be read • Each host contributes to the detection process • Problems • Positioned too high in the attack chain (the attacks reach the network driver) Tecniche di Sicurezza dei Sistemi

14. Different Types of IDSs Network IDS • Watch network traffic • Watch active services and servers • Report and possibly stop network level attacks • Advantages • Attacks can be stopped early enough (before they reach the hosts or applications) • Attack information from different subnets can be correlated • Problems • Encrypted data cannot be read • Annoyances to normal traffic if for some reason normal traffic is dropped Tecniche di Sicurezza dei Sistemi

15. 2. Different Types of IDSs Application-, Host- and Network IDS – Comparison Tecniche di Sicurezza dei Sistemi

16. Simple Process Model for ID Diagram Parse data, filter data and execute Detection Algorithms For example applications log network driver, or network cable Drop packets, send alerts, update routing tables, kill processes etc. Tecniche di Sicurezza dei Sistemi

17. IDS principle of detection Misuse Detection There are two basic methods used by ID Systems: misuse detection and anomaly detection. • Search attack signatures, which are patterns, byte code or expressions belonging to a specific attack. • often called signature-based detection • A signature is created by analysing an attack method • The patterns are stored inside the IDS Example Rule: Alert tcp !192.168.1.0/24 any -> 192.168.1.0/24 111 (Content: “|00 01 86 A5|”;msg:”External Mountd access”;) Tecniche di Sicurezza dei Sistemi

18. Example of a NIDS, snort • Enable NIDS mode of Snort # ./snort -dev -l ./log -h 192.168.1.0/24 -c snort.conf • The above command means that let Snort work as NIDS for the network 192.168.1.0/24 according to the rules inside snort.conf file. • Sample rule: • alert udp any any -> 192.168.1.0/24 5060 (content:"|01 6a 42 c8|"; msg: “SIP session signaling";) • The rules are modular and it is easy to add new rules. Typically the rules make alarms of all old security breaches so that you cannot notice any new breaches. Tecniche di Sicurezza dei Sistemi

19. IDS principle of detection Anomaly Detection “Distinguish abnormal from normal” • Threshold Detection • X events in Y seconds triggers the alarm • Statistical Measures • Current traffic profile matches the ”normal” profile • Rule-Based Methods • Jack never logs in at 6 to 8 AM • If Jack just sent email from Espoo office, he should not send email from New York office at the same time Tecniche di Sicurezza dei Sistemi

20. IDS principle of detection Anomaly/Misuse Detection – Comparison Tecniche di Sicurezza dei Sistemi

21. IDS response principles Responses • Alerts and notifications: email, SMS, pager (important issue: alert path must be bulletproof) • Increase Surveillance: log more • Throttling: slow down malicious traffic • Blocking Access: drop data, update firewall/router • Make Counterattack: Eye for an eye tactics • Honey Pots and Padded Cells: route the hacker to a fake system and let him play freely Tecniche di Sicurezza dei Sistemi

22. IDS problems in the detection stage Detection problems • True positive, TP, is a malicious attack that is correctly detected as malicious. • True negative, TN, is a not an attack and is correctly classified as benign. • False positive, FP, is not an attack but has been classified as an attack. • False negative, FN, is an attack that has been incorrectly classified as a benign. • Detection rate is obtained by testing the IDS against set of intrusive scenarios “…The false alarm rate is the limiting factor for the performance in an IDS”. Tecniche di Sicurezza dei Sistemi

23. Advanced IDS Techniques For Protection • Stream Reassembly: follow connections and sessions • Traffic Normalization: see that protocols are followed • Bayesian Networks: Data mining and decision networks • Graphical IDSs (for example GrIDS): use graphs to model attacks • Feature equality heuristics: port stepping, packet gap recognition • Genetic Programming, Human immune systems • Tens of research systems exist For Attacks • Evasion methods (fragmentation, mutation etc.) • IDS trashing (DoS tools to like stick/snot to crash IDS capability Tecniche di Sicurezza dei Sistemi

24. Evaluation of IDS • Type I error: (false negative) • Intrusive but not being detected • Type II error: (false positive) • Not intrusive but being detected as intrusive • Evaluation: • How to measure? • ROC - Receiver Operating Characteristics curve analysis - detection rate vs. False alarm rate • What else? Efficiency? “Cost?” Tecniche di Sicurezza dei Sistemi

25. Example ROC Curve IDS % Detect • Ideal system should have 100% detection rate with 0% false alarm % False Alarm Tecniche di Sicurezza dei Sistemi

26. Next Generation IDSs • Adaptive • Detect new intrusions • Scenario-based • Correlate (multiple sources of) audit data and attack information • Cost-sensitive • Model cost factors related to intrusion detection • Dynamically configure IDS components for best protection/cost performance Tecniche di Sicurezza dei Sistemi

27. anomaly data ID models (misuse detection) ID models ID models Adaptive IDSs ID Modeling Engine IDS anomaly detection semiautomatic IDS IDS Tecniche di Sicurezza dei Sistemi

28. Semi-automatic Generation of ID Models models Learning features patterns connection/ session records Data mining packets/ events (ASCII) raw audit data Tecniche di Sicurezza dei Sistemi

29. dst … service … flag %S0 h1 http S0 70 h1 http S0 72 h1 http S0 75 h2 http S0 0 h4 http S0 0 h2 ftp S0 0 The Feature Construction Problem dst … service … flag h1 http S0 h1 http S0 syn flood h1 http S0 h2 http S0 normal h4 http S0 h2 ftp S0 existing features useless construct features with high information gain How? Use temporal and statistical patterns, e.g., “a lot of S0 connections to same service/host within a short time window” Tecniche di Sicurezza dei Sistemi

30. Feature Construction Example • An example: “syn flood” patterns (dst_host is reference attribute): • (flag = S0, service = http), (flag = S0, service = http)  (flag = S0, service = http) [0.6, 2s] • add features: • count the connections to the same dst_host in the past 2 seconds, and among these connections, • the percentage with the same service, • the percentage with S0 Tecniche di Sicurezza dei Sistemi

31. Detection Models Dynamic Cost-sensitive Decision Making Real-time IDS Backend IDS FW Quick and dirty Best-effort in real-time Thorough and slow (scenario/trend) An Adaptive IDS Architecture Tecniche di Sicurezza dei Sistemi

32. Detecting Intruders • Commercially the most used IDS systems are probably misuse based Network ID Systems, but Host-level IDS is also needed. • As an example of a Host-level IDS let us look at LIDS for Linux. • The philosophy of LIDS is to have a three layer protection: • Firewall • PortSentry • LIDS • The firewall limits access to only allowed ports. In a Web-server only the TCP port 80 is absolutely necessary. • Disable ports which are not used, for instance by removing the daemons or by modifying /etc/inetd.conf. Leave only the basic activities needed. Tecniche di Sicurezza dei Sistemi

33. Detecting Intruders • PortSentry is put to some port, which is often scanned but not used in the system. • One should find suitable ports where to put PortSentry by looking at ports which are scanned often, like 143 or 111. • Typically nowadays hackers do sweep scanning looking at only one port in several machines. • PortSentry monitors activity on specific TCP/UDP ports. The PortSentry can take actions, like denying further access to the port. Tecniche di Sicurezza dei Sistemi

34. Detecting Intruders • This is based on the assumption that the hacker will first probe with a scanner the machine for weaknesses. • You install PortSentry in TCP-mode by portsentry -tcp • ports are in portsentry.conf -file. Tecniche di Sicurezza dei Sistemi

35. Detecting Intruders LIDS • LIDS is an intrusion detection system that resides in the Linux kernel. • It basically limits the rights of a root user to do modifications. It limits root access to direct port access, direct memory access, raw access, modification of log files, limits access to file system. It also prevents installation of sniffers or changing firewall rules. Tecniche di Sicurezza dei Sistemi

36. Detecting Intruders LIDS • An administrator can remove the protection by giving a password to LIDS, but if a hacker breaks into the root, he cannot without LIDS password do much damage. • Is this good? it certainly makes the life of a hacker more difficult, but what about a hacker getting into the kernel? • How nice it is being an administrator using LIDS? Tecniche di Sicurezza dei Sistemi