Intruders 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. 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.

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)

Unauthorized Use of Computer Systems Within Last 12 Months (source CSI/FBI Study) 1.Motivation for Intrusion Detection

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)

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) Different Types of IDSs There are Application-, Host- and Network IDS

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) Different Types of IDSs Application-, Host- and Network IDS

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 Different Types of IDSs Application-, Host- and Network IDS

2. Different Types of IDSs Application-, Host- and Network IDS - Comparison

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.

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.

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.

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

Example: ( anomaly detection engine---SPADE) [**] [104:1:1] spp_anomsensor: Anomaly threshold exceeded: [**] 08/22-22:37: :3246 -> VICTIM.HOST:80 TCP TTL:116 TOS:0x0 ID:25395 IpLen:20 DgmLen:48 DF ******S* Seq: 0xEBCF8EB7 Ack: 0x0 Win: 0x4000 TcpLen: 28 TCP Options (4) => MSS: 1460 NOP NOP SackOK [**] [104:1:1] spp_anomsensor: Anomaly threshold exceeded: [**] 08/22-22:22: :2065 -> VICTIM.HOST:27374 TCP TTL:108 TOS:0x0 ID:10314 IpLen:20 DgmLen:48 DF ******S* Seq: 0x63B97FE2 Ack: 0x0 Win: 0x4000 TcpLen: 28 TCP Options (4) => MSS: 1460 NOP NOP SackOK [**] [104:1:1] spp_anomsensor: Anomaly threshold exceeded: [**] 08/23-23:04: VICTIM.HOST: > :3486 TCP TTL:255 TOS:0x0 ID:0 IpLen:20 DgmLen:40 DF ***A*R** Seq: 0x0 Ack: 0x22676B9 Win: 0x0 TcpLen: 20 [**] [104:1:1] spp_anomsensor: Anomaly threshold exceeded: [**] 09/02-01:30: VICTIM.HOST:515 -> :1189 TCP TTL:64 TOS:0x0 ID:0 IpLen:20 DgmLen:60 DF ***A**S* Seq: 0x16FC5A7F Ack: 0x529F8CE7 Win: 0x16A0 TcpLen: 40 TCP Options (5) => MSS: 1460 SackOK TS: NOP TCP Options => WS: 0

Anomaly/Misuse Detection – Comparison IDS principle of detection

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

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”.

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

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.

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. 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.

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. 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?