Intrusion Detection Methods

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Intrusion Detection Methods

“Intrusion detection is the process of identifying and responding to malicious activity targeted at computing and networking resources.”

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The Seven Fundamentals

1. What are the methods used2. How are IDS organized3. What is an intrusion4. How do we trace and how do they hide5. How do we correlate information6. How can we trap intruders7. Incident response

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Some fundamental questions

• Are ID methods only suited for manual use by experts?

• Are ID methods well defined enough to be automated?

• What are some of the manual methods used by experts?

• What ID methods are available in tools today?

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ID methods

• Audit trail processing

• On-the-fly processing

• Profiles of normal behavior

• Signatures of abnormal behavior• Parameter pattern matching or anomaly discovery

Are the above methods independent? Dependant?Mutually exclusive?

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Audit Trail Processing

• Activities are first logged and stored in a log file via audit probs.

• Audit probes are [mostly] selected based on what constitutes security critical events.

• System and security administrators (and designers) are changed with enabling/disabling probs.

Auditing vs. Performance? What are the issues?What are the TCSEC requirements for Audit? (See Page 40)

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Case study: TCP logs

<src_ip, dst_ip, src_port, dst_port, protocol, time, direction, status>

Internal net (in)

External net(out)

log

Router/Gateway

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Case study: TCP logs (cont.)

<in,in, 4050, 80, tcp, 07:02:22, inbound, success>

<outx,gw, 6025, 23, tcp, 07:51:12, inbound, failure>




.

.

.

<outx,in, 3000, 23, tcp, 13:04:22, inbound, success>

<outy,gw, 6025, 23, tcp, 23:54:22, inbound, success>

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How much of the previous discussion can be automated?

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Examples of things to watch for!

• Users logging in at strange hours

• Unexpected reboots or clock changes

• Unusual error messages

• Failed login attempts

• Unauthorized use of the su command

• Users logging from unusual locations

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Problems to be considered while using logging systems

Most administrators don’t collect audits, and if they do, they rarely process them!

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Problems to be considered while using logging systems (cont.)• Large size of audit files

- About 5M per week for a workgroup server

- Becomes more problematic for centralized logging

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Problems to be considered while using logging systems (cont.)

• Degraded system performanceReached 85% on some typical unix and NT systems http://www.iamsam.com/papers/thesis/thesis.htm

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• Difficulty in protecting the log

- Log files growing smaller!

- Print everything

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• Unknown storage duration of logs

How long should logs be kept?

How long are they kept on your linux system?

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Unix Syslog

• Syslogd is a daemon (background process)• Receives message for the log file from:

– User processes running on the same mchaine (as syslogd) via /dev/log

– Kernel routines (/dev/klog)

– Processes on another machine via UDP port 514

• Syslogd defines an associated API for application authors

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# Log all kernel messages to the console.# Logging much else clutters up the screen.kern.* /dev/console

# Log anything (except mail) of level info or higher.# Don't log private authentication messages!*.info;mail.none;news.none;authpriv.none /var/log/messages

# The authpriv file has restricted access.authpriv.* /var/log/secure

# Log all the mail messages in one place.mail.* /var/log/maillog

# Everybody gets emergency messages, plus log them on another# machine.*.emerg *

# Save mail and news errors of level err and higher in a# special file.uucp,news.crit /var/log/spooler

/etc/syslog.conf

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F25 21:37:44 rnd PAM_pwdb[17775]: (sshd) session opened for user sherif by (uid=0)F25 21:40:00 rnd CROND[17784]: (root) CMD ( /sbin/rmmod -as)F25 21:42:18 rnd PAM_pwdb[17789]: (sshd) session opened for user sherif by (uid=0)F25 21:50:01 rnd CROND[17813]: (root) CMD ( /sbin/rmmod -as)F25 21:51:24 rnd PAM_pwdb[17789]: (sshd) session closed for user sherifF25 21:52:27 rnd PAM_pwdb[17775]: (sshd) session closed for user sherifF25 22:00:00 rnd CROND[17851]: (root) CMD ( /sbin/rmmod -as)F25 22:01:00 rnd CROND[17856]: (root) CMD (run-parts /etc/cron.hourly)F25 22:10:00 rnd CROND[17887]: (root) CMD ( /sbin/rmmod -as)F25 22:20:01 rnd CROND[17969]: (root) CMD ( /sbin/rmmod -as)F25 22:30:00 rnd CROND[17999]: (root) CMD ( /sbin/rmmod -as)F25 22:40:01 rnd CROND[18034]: (root) CMD ( /sbin/rmmod -as)F25 22:50:00 rnd CROND[18061]: (root) CMD ( /sbin/rmmod -as)F25 23:00:00 rnd CROND[18087]: (root) CMD ( /sbin/rmmod -as)F25 23:01:01 rnd CROND[18092]: (root) CMD (run-parts /etc/cron.hourly)F25 23:10:01 rnd CROND[18123]: (root) CMD ( /sbin/rmmod -as)F25 23:20:00 rnd CROND[18149]: (root) CMD ( /sbin/rmmod -as)F25 23:30:00 rnd CROND[18175]: (root) CMD ( /sbin/rmmod -as)F25 23:40:00 rnd CROND[18201]: (root) CMD ( /sbin/rmmod -as)F25 23:50:01 rnd CROND[18228]: (root) CMD ( /sbin/rmmod -as)F26 00:00:00 rnd CROND[18264]: (root) CMD ( /sbin/rmmod -as)F26 00:01:01 rnd CROND[18269]: (root) CMD (run-parts /etc/cron.hourly)F26 00:10:00 rnd CROND[18302]: (root) CMD ( /sbin/rmmod -as)F26 00:20:01 rnd CROND[18352]: (root) CMD ( /sbin/rmmod -as)F26 00:28:17 rnd PAM_unix[18386]: (system-auth) session opened for user root by sherif(uid=500)F 26 00:30:00 rnd CROND[18426]: (root) CMD ( /sbin/rmmod -as)

/var/log/messages

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F25 22:32:22 rnd sendmail[18009]: g1PKU1x18007:to=<[email protected]>,delay=00:02:21, xdelay=00:00:03, mailer=esmtp, pri=589605,relay=mx2.mail.yahoo.com. [64.157.4.88],dsn=2.0.0, stat=Sent (ok dirdel)

F25 22:32:42 rnd sendmail[18009]: g1PKU1x18007:to=<[email protected]>,delay=00:02:41, xdelay=00:00:20, mailer=esmtp, pri=589605,relay=ob-mail-com.mr.outblaze.com. [205.158.62.26],dsn=2.0.0, stat=Sent (g1PJVqt94451 Message accepted for delivery)

/var/log/mail

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SWATCH

• Simple and effective tool• Written in perl

/pattern/[, /pattern/] action[,action] duration

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Case Study : Secureview Firewall-1 Audit

Intranet InternetFirewall-1

Firewall-1log

OtherFirewall-1

Log Processing

Tools

ReportingModule

DataMart

DatabaseBuilder

AdminModule

Security Administrator

SecureITSecureView

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Mar 2 23:53:51 148.63.149.144:1072 -> 208.160.134.38:1214 VECNA ****P***

Mar 2 23:54:33 148.63.149.144:1072 -> 208.160.134.38:1214 VECNA ****P***

Mar 2 23:55:39 148.63.149.144:1072 -> 208.160.134.38:1214 VECNA ****P***

Mar 2 23:56:44 148.63.149.144:1072 -> 208.160.134.38:1214 VECNA ****P***

Mar 2 23:57:50 148.63.149.144:1072 -> 208.160.134.38:1214 VECNA ****P***

Mar 2 23:58:49 148.63.149.144:1072 -> 208.160.134.38:1214 VECNA ****P***

Mar 3 00:00:00 148.63.149.144:1072 -> 208.160.134.38:1214 VECNA ****P***

Mar 3 00:01:01 148.63.149.144:1072 -> 208.160.134.38:1214 VECNA ****P***

Mar 3 00:02:05 148.63.149.144:1072 -> 208.160.134.38:1214 VECNA ****P***

Mar 3 00:03:11 148.63.149.144:1072 -> 208.160.134.38:1214 VECNA ****P***

Mar 3 00:04:14 148.63.149.144:1072 -> 208.160.134.38:1214 VECNA ****P***

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On-the-fly processing

• Timeliness

• Processing method

• Storage requirements

• Information capacity

Probe Ponts selected by system administrators

TargetSystem

TargetSystem

IntrusionDetectionSystem

on-the-fly processing

Direct system feeds

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Network management and NIDS

• Use SNMP and RMON (RFC 1271) as a basis for ID collection and processing– Analyze traffic history and statistics– Examine network trends– initiate alarms– Traffic generation for testing

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Netmetrix

Enterprise WAN(SNMP transport)

Enterprise WAN(SNMP transport)

LanProbe

LanProbe

LAN(Ethernet)

LAN(token ring)

Noninvasivemonitors

Analysis applicationsfor trending, alarms, analysis, display, etc

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Case Study : NFR

TargetSystem

PacketSucker

DecisionEngine

Query

GUI

Alert Manager

Filter 2

Filter 3

Filter N

Filter 1

Backend

Backend

Backend

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Methods for extracting traffic from the network for processing• In-line diversion of traffic by network

components

• Off-line extraction (passive sniffing)– Most used: Ethernet promiscuous mode– Other examples:

• Serial lines

• Wireless networks

• Tempest effect aka The van Eck effect

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Case Study : BorderGuard Firewall Extraction for NetRanger Processing

• NSX device : local intrusion Monitoring Function

ProtectedSystem

BorderGuardFirewall

TargetSystem

NSXIntrusion Detection

Diverted Traffic forNetRanger IntrusionDetection

Gateway Traffic

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Normal Behavior profiling

User Profiling Method

SecurityAdministrator

UserProfile

UserActivity

UserActivity

Knowledge Base(Comparable users)

RefineUpdate

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Normal Behavior profiling

• Initial profiling of new systems and users based on estimations of expected behavior

• Observed user and system behavior should be used to fine-tune profiles

• Information from other (external) resources is used to improve the accuracy of prediction

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Concept of Profile-based Processing

System ActivitySystem Activity

Activity Observed(audit log)

Activity Expected(Profiles)

Compare and Respond

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Case study: IDES model

• Audit trail information is collected in protected logs

• Profile based tools as used for off-line analysis

SystemActivity

SystemActivity

AnomalyRecords

AuditTrail

User/SystemProfiles

IDESProcessing

Alarms

IDES Design

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Case study: IDES model (cont.)

<subject, object, profiles, audit-records, anomaly records, alarms>

• Subjects and Objects: from classical INFOSEC view of the initiator and the target of an activity

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Case study: IDES model (cont.)

• Profile: Characterization of behavior

• Audit records: the data structures used to capture the system’s observed behavior

• Anomaly records: the data structures used to capture anomalous behavior

• Alarms: problem reporting methods

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Toll fraud and similar problems

• How can toll fraud-like problems be solved using “Normal Behavior profiling?”

• How about credit card fraud?

• Phone card fraud?

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http://www.atcomm.com/advisor/basics/call-account.htm

• Boost Security– Highlight Suspicious Activity and Review

Unrecognizable Call Data for Hacker Detection– Prevent/Locate Unauthorized System Access – Real Time Notification of Exception Calling – Track After Hours Security Guards– Detect Bomb Threats– Selective Reporting/Display for Top Secret/Sensitive

Materials– Account for Calls But Delete Detail (Call Processing)– Password Security to Prevent Moving from Call

Processing – Keyboard Macro Available to Provide Additional

Security

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The Abnormal Behavior (Attack) Signature Method

• Commonly used in on-the-fly IDS

• Attack signatures– May require temporal and state machine like

modeling

• Special character strings– E.g.: /etc/password in an ftp session

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TargetSystem

TargetSystem

Strings

Profiles

Intrusion

Detection

Systems

Probe Point Feed

Selected via traffic content modeling of attack

Selected viaactivity sequencemodeling of attack

Should correlate string and profile based processing

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Case Study: SNORT rules

• http://www.snort.org/docs/writing_rules/

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alert tcp $EXTERNAL_NET any -> $HOME_NET 21 (msg:"FTP .forward"; content: ".forward"; flags: A+;reference:arachnids,319; classtype:suspicious-filename-detect; sid:334; rev:2;)

alert tcp $EXTERNAL_NET any -> $HOME_NET 21 (msg:"FTP .rhosts";flags: A+; content:".rhosts"; reference:arachnids,328; classtype:suspicious-filename-detect; sid:335; rev:2;)

alert tcp $EXTERNAL_NET any -> $HOME_NET 21 (msg:"FTP CWD ~root"; content: "cwd ~root"; nocase; flags: A+;reference:arachnids,318; classtype:bad-unknown; sid:336; rev:1;)

alert tcp $EXTERNAL_NET any -> $HOME_NET 21 (msg:"FTP EXPLOIT aix overflow";flags: A+;dsize:>1300; content:"CEL "; reference:arachnids,257; classtype:attempted-admin; sid:337; rev:1;)

alert tcp $EXTERNAL_NET any -> $HOME_NET 21 (msg:"FTP EXPLOIT format string"; flags: A+; content: "SITE EXEC |25 30 32 30 64 7C 25 2E 66 25 2E 66 7C 0A|"; depth: 32; nocase; reference:arachnids,453; classtype:attempted-user; sid:338; rev:1;)

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Parameter pattern matching or anomaly discovery

• Based on continuous monitoring of network and systems attributes

• The monitoring is not necessary security focused

• The use of day-to-day operational experience and the basis for detecting anomalies

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Target System

(network, OS,application, etc

Target System

(network, OS,application, etc

Operational View(Patterns)Noarmal

Operations

These monitoringoperations maynot be disciplined or predictable

Normal systemOperation andAdministration

IntrusionDetectionSystem

Interpretationsof Patterns(intrusion detection)

This interpretationis triggered by and detection of change from normal

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recent criticism of intrusion detection method• on the fly traffic interpretation problem

• server audit interpretation problem

• fail-open nature of intrusion detection

• intrusion detection methods may be vulnerable to insertion attacks

• intrusion detection methods may be vulnerable to evasion attacks

• Intrusion detection methods may be vulnerable to denial of service attacks

Documents

Intrusion Detection Methods