1. Design Lines for a Long Term Competitive IDS Erwan Lemonnier KTH-IT / Defcom

2. Thesis’s subject: An analysis of IDSs difficulties and how to solve them. Two approaches are explored:  Designing efficient filters  Improving IDS architecture (MIDS) Design Lines for a Long Term Competitive IDS - Erwan Lemonnier - 2001/10/08

3. Plan of Presentation  Introduction to IDSs  IDS challenges  solution 1: Efficient filter design  solution 2: MIDS, an alternative IDS architecture Design Lines for a Long Term Competitive IDS - Erwan Lemonnier - 2001/10/08

4. Introduction to IDSs IDSs are programs monitoring a computer system (network, host) to detect intrusion attempts. Typically made of a sensor, some filters, an alert-flow and a monitoring center. Design Lines for a Long Term Competitive IDS - Erwan Lemonnier - 2001/10/08 Host / Network SENSOR SENSOR API filter Monitoring Center Alert-flow Filter Sensor Monitored Data Monitored System

5. Sensors: host based / network based Filters: small programs analyzing sensor data to detect intrusions. Detection Strategies:  Signature  Anomaly detection (protocol anomaly) Design Lines for a Long Term Competitive IDS - Erwan Lemonnier - 2001/10/08 Protocol Standard Pratical Usage Attaques

6. IDS Challenges Insertion & Evasion Alert-flow control Encrypted traffic Learning from antiviruses Technical obstacles Design Lines for a Long Term Competitive IDS - Erwan Lemonnier - 2001/10/08

7. Insertion & Evasion Efficient detection theoretically implies knowledge of monitored system’s state and rules Despite standards, systems are implemented differently. Ex: different TCP/IP stack implementation => always make false assumptions on monitored system’s reactions => possible to shape the traffic so that the IDS accepts a packet but not the monitored system (Insertion) or the contrary (Evasion) Design Lines for a Long Term Competitive IDS - Erwan Lemonnier - 2001/10/08

8. Alert-flow control challenges  False positives Can not be avoided Increase with traffic  Hiding attacks  IDS evasion  Alert flood  Slow rate attacks  Distributed attacks Design Lines for a Long Term Competitive IDS - Erwan Lemonnier - 2001/10/08 need for intelligent alert-flow processing components

9. Encrypted Traffic Network based IDS can’t monitor encrypted traffic Only known solution = decryption proxy but hard to deploy ex: https Design Lines for a Long Term Competitive IDS - Erwan Lemonnier - 2001/10/08 Client HTTPS Decryption Proxy HTTP/SSL clear HTTP HTTP Server Network Based IDS

10. Learning from Antivirus Virus/Antivirus similar to Attacks/IDS similar techniques (signature, anomaly) probably similar results, but antivirus are more mature Evasion race (IDS evasion, polymorphism, etc.) need for reactive/automated filter updating process Anomaly detection effective if used with signatures Design Lines for a Long Term Competitive IDS - Erwan Lemonnier - 2001/10/08

11. Technical obstacles resistance to fragmentation/insertion/evasion => efficient TCP/IP stack monitoring high rate traffic => load balancing Design Lines for a Long Term Competitive IDS - Erwan Lemonnier - 2001/10/08

12. Solutions ? approach 1: improving filters approach 2: alternative IDS architectures Design Lines for a Long Term Competitive IDS - Erwan Lemonnier - 2001/10/08

13. Efficient filters: improves detection & alert-flow control how ? mixing signature & anomaly detection protocol anomaly analysis engine enables efficient signature matching internal caching and filtering of alert-flow reduces volume of alert-flow more acurate analysis (corelation) Design Lines for a Long Term Competitive IDS - Erwan Lemonnier - 2001/10/08

14. Efficient filters: Telnet filter example Design Lines for a Long Term Competitive IDS - Erwan Lemonnier - 2001/10/08

15. Efficient filters: TCP filter example Design Lines for a Long Term Competitive IDS - Erwan Lemonnier - 2001/10/08

16. Alternative IDS structure IDSs are alert-flow management systems. Focus on: multiplying alert sources merging alert-flows from different sources processing intelligently the alert-flow Design Lines for a Long Term Competitive IDS - Erwan Lemonnier - 2001/10/08

17. Suggested Architecture: Multi IDS Design Lines for a Long Term Competitive IDS - Erwan Lemonnier - 2001/10/08 Monitored System snort ISS NFR Host / Network Monitoring Center Monitored Data alert flow merger Corelation Engine IDS alert-flow multiple IDSs host & network based multiple filtering techniques alert-flow corelation

18. Host based sensors: detect the host side of an attack hidden to network based IDS (evasion, encryption, etc.) Multiple different network based sensors: Many different TCP/IP stack implementation => reduce risk of evasion/insertion Alert-flow merging and processing Merging alert-flow Shaping alert-flow to increase its informational load Alert corelation Data mining solve evasion/insertion, alert flow control & encryption problems Design Lines for a Long Term Competitive IDS - Erwan Lemonnier - 2001/10/08

19. Remaining problems: reactive/automated filter updating process => by out-sourcing IDS management to a specialized entity alert-flows corelation: we are now working on it ! Conclusion Intelligent data and alert-flow processing is the future of IDSs. Design Lines for a Long Term Competitive IDS - Erwan Lemonnier - 2001/10/08