Network Security and Intrusion Detection

1. Network SecurityandIntrusion Detection Survey of the Art and Practice Dr. Michah Lerner AT&T Labs 15-August-2000 AT&T

2. Outline • Model • Principles • Assumptions • Methods • Products No silver bullets Published sources only Note: this talk describes some attack models. If you’d like “try them out”, don’t! AT&T

3. Intrusion Detection Systems, IDS • Identified by Dorothy Denning in 1987 IEEE Software Engineering • Protect systems and networks from threats, vulnerabilities, and intrusions • Art includes: • “Bro: A System for Detecting Network Intruders in Real Time” (Vern Paxon) • JiNao – Protect link state routing – Felix Wu • Rule-based expert system, statistical analysis, protocol analysis, OSPF MIB, distributed programming interface (DPI) • Vendors include: • Amazon.com lists 171 security products • Axent (NetProwler, and Tivoli modules), ISS, Network Associates, Cisco AT&T

4. A Story … • Jane the Dandelion wine merchant • Running SSL to protect her eCommerce site • Coalition against Dandelion Wine • Quietly launches a chosen ciphertext attack against her SSL server (Daniel Bleichenbacher, LNCS 1462, 1998) • Exploit weakness in SSL V.3.0 • Generate many authentication requests • SSL reports which ones were incorrectly formatted • The Coalition obtained her master secret! • They tested about one million chosen ciphertexts – on her server! • She just thought that SSL was slow! • IDS would have found incomplete SSL handshakes, and probably foiled the intruder AT&T

5. Assumptions • Assumptions … • RFC 1636 – encryption essential to security • Open networks violate this assumption • Encryption should protect control information, as well as contents • See section 7.3 of the RFC • In attack from Vi net  Vj assume only one of Vi, Vj is the attacker • DDOS violates this assumption • Assumptions are “sometimes” wrong • Replay attack can masquerade with encrypted data • Distributed attacks can leverage multiple attackers • Encryption can be broken AT&T

6. Concept – Collection & Analysis CERN European Laboratory for Particle Physics Birth Place of “The Web Browser” – http://www.cern.ch • Every time something suspicious is detected, the session’s security weight is increased • When the security weight gets higher than a given threshold, detailed monitoring starts • Encryption was, until recently, not allowed by the French law  Not much used for first break-in discovery, but invaluable for security incident analysis and follow-up: it answers typical questions like: When did the first break-in happen? Which other systems may have been attacked? Which other services on the attacked system may have been compromised? Security officer Reports Filter Suspicious behavior Network Database Analyzer AT&T

7. Intrusion – Examples • Denial of Service • Hijacking of session or router • Theft • Resources – bandwidth theft or blockage • Identity • Information AT&T

8. Intrusion at any layer or sliceDifficult and Complex Problem AT&T

9. 1For discussion purposes only Mobsters101 – How to Intrude1 • Resources • Exhaust, overload or consume • Control Functions • Undermine direct control protocols • Assert authentication or authorization contrary to policy • Block authentication or authorization • Undermine indirect control • Subvert timing or other policing methods • Transport Functions • Transmit forged content • Modify, Read or Block content • “Many attackers use tools like COPS or SATAN, which automate the process of checking for known bugs in remote network systems. These freely available tools, as well as commercial tools such as ISS’s Internet Scanner, are designed to help systems administrators audit their own networks, but are equally useful to an attacker.” [Wallach99] • See http://www.cert.org/advisories AT&T

10. Intrusion – Definition • Intrusion • Violation of the network policy, even where the policy is not completely stated • Policy • Allocation, usage and return of resources • Possibly multiple policies active on a network • Varied requirements of business, administration or trust • Resources • Finite • Independent • Layered • Protocol-driven • Protocols • Efficient, not perfect • IP spoofing – packets are not uniquely att-ributable to the origin • Costly to stop AT&T

11. Prevention – Policies & Assurances • Violations of policy may define intrusion • Except: • Seldom have such a precise policy in IP • The policy could be buggy • New applications could violate the policy • Cost is prohibitive for many applications • Can plug anything into the Internet – not just “safe” applications. IEEE 802.3 (Ethernet) is ubiquitous • An alternative to formal policy is assurances • General policy, but less rigorous • Availability – connections, bandwidth, low delay • Integrity – privacy, reliability, and low error-rate AT&T

12. Detection • Assurances are threatened by: • Misuse– specific attack behavior • Based on expert knowledge of patterns associated with attack • Patterns of misuse defined by experts, or by machine learning – should not occur • Examples: • Mismatched SYN/ACK • Same authenticated user from multiple locations? • Multiple failed authentications? From different address?? • Problem: only recognizes anticipated threats (but can combine several threats that might otherwise be missed) • Anomalous use– possible attack • Recognize increased risk to network • Compare actual with expected behavior • Load rising atypically? AT&T

13. How to Protect the Assurances? • Redundancy • Makes it harder to corrupt • Make it easier to identify corruption • May make it easier to locate the corruption • Explicit redundancy: add to network or data • Tags and attributes • Input/output validation • Implicit redundancy: already in the network • Anonymous – timing • Private – network attributes • Content – privacy and easily evaded • Per-protocol or general properties • State-machine compliance? • Frame-format? AT&T

14. Prevention Define multiple layers Define behavior of each layer, including resources Enforce each behavior Prohibit actions that may compromise the behavior Examples IP DDOS does not affect ATM integrity Replay of short-lifetime HTTP cookies is traceable Link-layer marking Ingress/egress filtering End-to-end coordination Detection Identify correct behavior Reinforce or augment Redundancy Format (protocol) Augmentation (tags) Validations Characterize activities Recognize anomalies Unusual transit duration, route, or augmentation Item – invalid packet header Aggregate – bad path or invalid protocol sequence Honeypot traces Two Keys to Protection AT&T

15. Explicit Redundancy – Protection • Content transformation • SSL • Cookies • Protocol hardening against adversarial “errors” • IPSec • Invalid session properties (i.e. stale keys, invalid context or content) may indicate attack • Packet augmentation • Security labels • Properties inherited from ingress • Requirements incumbent upon egress • Min/max trust and validation of information flow1 • Management at Ingress/Egress • Interaction with authentication and multiple domains AT&T

16. Implicit Redundancy – Detection • Packet • Well-formed packets (protocol-compliant) • Well-defined packets (service behavior) • Source, destination, format • May validate endpoints and actions • Traffic profile • Acquire by observation of usage • Statistical model – “distinctive characteristics (packet size, timing) … not on connection contents” • Resists encryption, and preserves privacy • Database of representative samples • Does the traffic profile fit the source/destination profiles? AT&T

17. General Technique • Collecttraffic and audit information • Protocol analysis • Various sensors • Content-independent sensors may work even on encrypted data • State-based sensors evaluate the trustworthiness of connection path • State-free sensors operate without change to firewall or network-element • Computepatterns of misuse or abuse • Recognize patterns of a possible attack • Previously observed or predicted attack patterns • Uncharacteristic changes in predicted performance AT&T

18. Information to Collect • Audit information • Management information bases (MIBS) and logs • After-the-fact analysis of traffic artifacts • Historical information • Recognition of previously used contents, such as serial numbers, someone else’s password, etc. • Strength of evidence follows the strength of the content source • Distributed • Exchange data on suspected intrusions (IETF IDWG) • Information from IP authentication systems AT&T

19. Information to Compute • Attack signatures • Hard problem – needs attack models to organize data • Attacks are often distributed – requires coordination • ISS publishes about 350 Real Secure Signatures at http://www.iss.net • Backdoors • Denial of Service • Distributed Denial of Service • OS Sensor • Suspicious Activity • Unauthorized Access Attempts • Only three detect RIP attacks on routing • None of the published signatures mention streaming, VoIP, MPEG, Quality of Service, or attacks on OSPF AT&T

20. Detailed Taxonomy • Knowledge-based • Expert systems; Signature analysis • Petri nets; State-transition analysis • Behavior-based • Statistics; Expert systems • Neural networks; “User Intention” model Source: IBM RZ 3176 (# 93222) 10/25/99 Computer Science/Mathematics (23 pages). A ReviseTaxonomy for Intrusion-Detection Systems by Hervé Debar, Marc Dacier, Andreas Wespi AT&T

21. Information Collection Tools • Tcpdump • Bro • NetMon • Snort • All canuse rules AT&T

22. Protocol Monitoring • Validate Appropriate Traffic Flows: • Multiple granularities of description • Recognize change from the behavior • Activation/deactivation of connections • Correlation/evaluation of connection attributes • How • Protocol scrubbing [InfoComm 2000] • State machines for correct protocol flow • Error states for erroneous traffic • Pattern recognition • Simulation/validation of expected behaviors • Does the expected response follow, or something else? AT&T

23. Declarative Language Russel Rules automata ASAX and Russel (RUle-baSed Sequence Evaluation Language) • State full event detection • Correlation of events across multiple hosts • consolidate intrusion evidence from several scattered sources and correlate them intelligently at a central location. FW-1 • SYN-Flood • IP spoof • Port Scan • Host Scan • etc. Router FUNDPUniv. Internet ISP Sniffer ASAX Source: Aziz MounjiAbdelaziz.Mounji@swift.com AT&T

24. Automatic Actions • Disable account • Log to file • SNMP traps • Email Sec-Ad • Exec any command • Send event to manager Interface with C Evtn Evt1 Evt2 Event Stream time Rule1(uid) Rule1(uid) Rule1(uid) State full Detection Rulek(x,y) Rulek(uid) Rulek(uid) Russell -- ASX AT&T

25. What if Alert? • Block offending traffic sources • Terminate suspicious processes • Coordinate with multiple domains • Intruder Detection and Isolation Protocol (IDIP) • Trace • Report • Directive (discovery coordinator) AT&T

26. Products(Names changing all the time) • Boundary controllers • NAI Gauntlet, ARGuE, MPOG, etc. • Secure Computing Sidewinder • Detectors • Axent, Cisco • SRI Emerald expert-system • NAI CyberCop • ISS RealSecure • NFR www.nfr.net • Event-based traffic analysis, pattern matching, aggregation and adaptation • SUNY, BRO, CIDF, IDIAN, DPF packet filter compiler … AT&T

27. Vendors and Products – Tivoli Compatibility Source: RZ 3253 (# 93299) 06/26/00; Computer Science 45 pagesIntegration of Host-based Intrusion Detection Systems into the Tivoli Enterprise Console, Christian Gigandet (IBM Research; Zurich Research Laboratory) AT&T

28. Cisco Intrusion Detection System• NetSonar (Scanner)• NetRanger (Monitor) • The Cisco Secure IDS includes two components: Sensor (renamed NetSonar) and Director (renamed NetRanger). • Cisco Secure IDS Sensors, which are high-speed network "appliances," analyze the content and context of individual packets to determine if traffic is authorized. AT&T

29. AT&T

30. ISS • RealSecure • Network engine resides on PC, monitors network transmissions for “signs of abuse and attack” • About 350 attack signatures currently published AT&T

31. APIs solve top 4 problems • ID module embedded in router/switch/firewall: • Evaluates all incoming and outgoing traffic for intrusions across all ports • Switching. Monitors heavily routed or switched networks at the most heavily-trafficked network junctions. • Speed. May also address speed issues by embedding ID in higher-performance hardware. • ID module running on adapter card: • Processor provides most of the analysis. • Speed. Hardware assist with packet classification provides wire-speed intrusion detection. • Security is painful. Shrink-wrap ID engine -- easy to install, easy to manage with relatively low cost. • ID module as an ASIC: • ID as a true design component. Installed on networking backplane, e.g. multi-gigabit switch, Probably only way to handle • Switching. Embedded in high-performance network device allows access to all packets at single location. • Speed. Wire-speed intrusion detection. • ID module embedded in host protocol stack: • Attached to protocol stack above encryption layer. • Encryption. Allows intrusion detection to exist in the presence of encrypted traffic while still providing adequate value. AT&T

32. CyberSafe Centrax AT&T

33. Summary • Maintain integrity: • Per layer • Per slice (protocol) • Validate packets • Ingress/egress counters • Squelch attack sources that do not comply with reasonable usage • Test carefully to ensure not a new application • Streaming media is not a UDP attack! • Measure and understand “flow” properties • Recognize statistically significant variation from these path properties AT&T

34. Backup Slides A bit more formality A glimpse at some academic research AT&T

35. Assumptions • Assumptions • RFC 1636 – encryption essential to security • Open networks violate this assumption • Encryption should protect control information, as well as contents • In attack from Vi net  Vj assume only one of Vi, Vj is the attacker • DDOS violates this assumption • Assumptions are sometimes wrong • Replay attack can masquerade with encrypted data • Distributed attacks can leverage multiple attackers • Encryption can be broken AT&T

36. General Network Model(circumscribes problem domain) • G = (V, E) • Path = {Vin, {Ej}, {Vj}, … {Ek}, {Vk}, {El}, {Vout}} • Path consists of vertices and edges • Edges E: • Propagate signal • Vertices V: • Receive signal • Compute output • Emit signal AT&T

37. Network Model • Edges (links) • Signal propagation • Impairments due to random noise • Redundancy manages noise, fade or analog error • Detect and correct by protocols through algebraic redundancy • Vertices (routers/switches) • Aggregate bits into packet • Classify and enqueue packet • Packet-type and priority (UDP? TCP? ICMP? RSVP?) • Loss due to load variation and queue size • Detect and correct by redundant payload or retransmission • Dequeue packet • Data packet: compute output as f(packet, control) • Control packet: modify control as f(packet, control) AT&T

38. Vertex Control function f(packet,control) • Data packet: • Pure IP: f(packet, control) is nearly the identity function • modify TTL, next-hop, etc • Proxy or active protocol: f(packet, control) not identity • Augment packets in more complex “custom” ways • Control packets: • Routing: static or dynamic • Resource: modify resources, i.e. queues, priorities • Behavior: modify function, i.e. classifier, marking, etc. AT&T

39. Monitoring Entity Signatures • Entity output descriptions • Compute usage signatures (local and complete) • Entity to neighbors • Entity to endpoints • Entity input descriptions: • Receivers compute signature of received data • Comparisons • Entities exchange signatures (or log centrally) • Anomaly detected from signature mismatches AT&T

40. Originator Routing Protocol OSPF Routing Protocol EIGRP Routing Protocol BGP RIB RIB RIB Âû¸£ IDS MIB Protocol Analysis Statistical Analysis JiNao SNMPv3 Eng. Decision Module Detection Module Info. Abst. Module FIB Where should I forward this packet? Prevention Module Security Officer Interception Module Protocol Engine Router/OS Kernel Network JiNao – Protect Link-State Routing Finite state machine with timing analysis, verifies Validity of OSPF actions, and guards against any intrusion – even one with “valid” security credentials AT&T