Intrusion Detection Systems

Tecniche di Sicurezza dei Sistemi2 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 Sistemi3 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 Sistemi4 What is Intrusion Detection Intrusion detection systems (IDSs) are designed for detecting, blocking and reporting unauthorized activity in computer 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 Sistemi5 Unauthorized Use of Computer Systems Within Last 12 Months (source CSI/FBI Study) 1.Motivation for Intrusion Detection

Tecniche di Sicurezza dei Sistemi6 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%) Most Common Attacks (source CSI/FBI) 1.Motivation for Intrusion Detection (Red color shows the attack types, which IDS can decrease)

Tecniche di Sicurezza dei Sistemi7 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 Sistemi8 Prevent Why Is Intrusion Detection Necessary? Detect React/ Survive Security principles: layered mechanisms

Tecniche di Sicurezza dei Sistemi9 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 Sistemi10 Components of Intrusion Detection System Audit Data Preprocessor Audit Records Activity Data Detection Models Detection Engine Alarms Decision Table Decision Engine Action/Report system activities are observable normal and intrusive activities have distinct evidence

Tecniche di Sicurezza dei Sistemi11 Different Types of IDSs 1. Application based; 2. Host based; 3. Network based.

Tecniche di Sicurezza dei Sistemi12 Application IDS –Watch application logs –Watch user actions –Stop attacks targeted against an application Different Types of IDSs Advantages Encrypted data can be read Problems Positioned too high in the attack chain (the attacks reach the application)

Tecniche di Sicurezza dei Sistemi13 Host IDS –Watch kernel operations –Watch network interface –Stop illegal system operations –Drop attack packets at network driver Different Types of IDSs 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 Sistemi14 Network IDS –Watch network traffic –Watch active services and servers –Report and possibly stop network level attacks Different Types of IDSs 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 Sistemi15 2. Different Types of IDSs Application-, Host- and Network IDS – Comparison

Tecniche di Sicurezza dei Sistemi16 Diagram Simple Process Model for ID For example applications log network driver, or network cable Parse data, filter data and execute Detection Algorithms Drop packets, send alerts, update routing tables, kill processes etc.

Tecniche di Sicurezza dei Sistemi17 Misuse Detection IDS principle of detection Alert tcp ! /24 any -> / (Content: “| A5|”;msg:”External Mountd access”;) – 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: There are two basic methods used by ID Systems: misuse detection and anomaly detection.

Tecniche di Sicurezza dei Sistemi18 Example of a NIDS, snort Enable NIDS mode of Snort #./snort -dev -l./log -h /24 - c snort.conf The above command means that let Snort work as NIDS for the network /24 according to the rules inside snort.conf file. Sample rule: alert udp any any -> / (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 Sistemi19 Anomaly Detection IDS principle of 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 from Espoo office, he should not send from New York office at the same time

Tecniche di Sicurezza dei Sistemi20 Anomaly/Misuse Detection – Comparison IDS principle of detection

Tecniche di Sicurezza dei Sistemi21 Responses IDS response principles Alerts and notifications: , 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 Sistemi22 Detection problems IDS problems in the detection stage 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 Sistemi23 Advanced IDS Techniques 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 Protection For Attacks Evasion methods (fragmentation, mutation etc.) IDS trashing (DoS tools to like stick/snot to crash IDS capability

Tecniche di Sicurezza dei Sistemi24 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 Sistemi25 Example ROC Curve Ideal system should have 100% detection rate with 0% false alarm % Detect % False Alarm IDS

Tecniche di Sicurezza dei Sistemi26 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 Sistemi27 Adaptive IDSs IDS ID Modeling Engine anomaly dataanomalydetection semiautomatic ID models (misuse detection)

Tecniche di Sicurezza dei Sistemi28 Semi-automatic Generation of ID Models models raw audit data packets/ events (ASCII) connection / session records features patterns Data mining Learning

Tecniche di Sicurezza dei Sistemi29 The Feature Construction Problem flagdst …service … h1 http S0 h2 http S0 h4 http S0 h2 ftp S0 syn flood normal existing features useless dst …service … h1 http S0 h2 http S0 h4 http S0 h2 ftp S0 flag %S 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 Sistemi30 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 Sistemi31 An Adaptive IDS Architecture FW Quick and dirty Real-time IDS Best-effort in real-time Backend IDS Thorough and slow (scenario/trend) Dynamic Cost-sensitive Decision Making Detection Models

Tecniche di Sicurezza dei Sistemi32 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 Sistemi33 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 Sistemi34 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 Sistemi35 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 Sistemi36 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?