EE579S Computer Security

Transcript EE579S Computer Security

EE579T / CS525T Network Security 11: Intrusion Detection Systems; Wireless Security

Overview of Tonight’s Class

• Review last week’s lesson • Final Exam – On the web page – Due to me electronically in 2 weeks (26 Apr) • Project Scheduling – Presentations on 15 April – Keep presentations to 25 minutes including Q&A – Let’s have volunteers for each time slot, keeping in mind your work schedules • Intrusion detection systems • Wireless security Spring 2005 © 2000-2005, Richard A. Stanley EE579T/11 #2

Summary

• SNMP is widely-used for managing clients distributed across a network • SNMPv1 is simple, effective, and provides the majority of SNMP service in the field • SNMPv2 adds some functionality to v1 • SNMPv3 is a security overlay for either version, not a standalone replacement • SNMP security is a major issue!

Intrusion Detection Systems

• Oddly enough, these are systems designed to detect intrusions into protected systems • Security intrusion (per RFC 2828): – A security event, or a combination of multiple security events, that constitutes a security incident in which an intruder gains, or attempts to gain, access to a system (or system resource) without having authorization to do so.

What’s a Security Incident?

• A security event that involves a security violation. (See: CERT, GRIP, security event, security intrusion, security violation.) • In other words, a security-relevant system

event in which the system's security policy is disobeyed or otherwise breached

Why Do We Need This?

• With the exception of authentication systems, most of the defenses we have studied up to now are directed towards intruders coming from outside the firewall • These systems are not perfect--some intruders will get through • Moreover, defenses such as firewalls cannot protect against intruders on the inside Spring 2005 © 2000-2005, Richard A. Stanley EE579T/11 #6

Intrusion Detection Functions

• Monitor protected networks and computers in real time (or as close to real time as is practicable) • Detect security incidents – Requires a policy, and a way for the IDS to know what that policy is • Respond – Raise an alarm – Send some automated response to the attacker Spring 2005 © 2000-2005, Richard A. Stanley EE579T/11 #7

IDS vs. Auditing

• Audits tend to be

a posteriori

– But an IDS can be seen as performing a constant, near real time audit function • To perform an audit, you need to know what the policy is – Audits measure departures from the policy norms – Audits depend on system logs Spring 2005 © 2000-2005, Richard A. Stanley EE579T/11 #8

Early IDS’s

• Emulated the audit function – Crawled the logs, looking for deviations from policy-permitted actions – Intent was to speed up the audit, making it nearly real time – Still a useful approach • IDS technology has been around only since the early 1990’s; not too mature Spring 2005 © 2000-2005, Richard A. Stanley EE579T/11 #9

IDS Uses

• Monitor system usage – Determine access, usage patterns – Plan for capacity engineering • Monitor specific problem areas • Serve as a deterrent – Sort of like the “burglar alarm” label on a house, even if there is really no alarm Spring 2005 © 2000-2005, Richard A. Stanley EE579T/11 #10

Log Files

• Are evidence if an intrusion occurs – Must be stored in their original, unmodified form, otherwise inadmissible in court – Provide data from which trends can be deduced – Can be subjected to forensic analysis – Probably needed to assess level of system compromise/damage and to restore to state prior to intrusion Spring 2005 © 2000-2005, Richard A. Stanley EE579T/11 #11

Legal Issues - 1

• Privacy of your employees – Courts have held that employees have little expectation of privacy in the workplace, especially if told so at the outset • email can be monitored at work by employer • phone calls can be monitored at work by employer • doing either of these things outside the workplace violates the wiretap statutes (18 USC § 2516, etc.) Spring 2005 © 2000-2005, Richard A. Stanley EE579T/11 #12

Legal Issues - 2

• What if the IDS discovers illegal acts being performed on/by your network?

– Employees using the network for illegal activities – Outsiders having planted zombie programs so that your system attacks others – What is your responsibility and liability?

Legal Issues - 3

• This may be a Catch-22 issue – If an attacker is using your system, law enforcement may want you to continue to allow that to happen so they can apprehend the attacker • If you interrupt the attack, could be interpreted as obstruction of justice – But, if you allow the attack to continue, you may be liable for damages to those attacked • Get legal advice--beforehand!

What About Automated Response?

• Tempting capability • If attacking your system is illegal, what makes your attack on the attacker in response less illegal?

• What if you are, or are acting on behalf of, a governmental entity and the attacker is also a governmental entity?

–

Casus belli

Sensor

IDS Architecture

Console

• Monitors and controls sensors – Sets policy, alarm levels, etc.

IDS Types

• Network-based (NIDS) – Monitors the network backbone • Network node-based (NNIDS) – Monitors network nodes, not the backbone • Host-based (HIDS) – This is the “log crawler” that started it all • Gateway (GIDS) – NIDS in series with the network Spring 2005 © 2000-2005, Richard A. Stanley EE579T/11 #18

What Can It See?

• Network packets • OS API calls • System logs • How do we merge this data to detect intrusions?

Host-Based

• Sits on a host as a background task • Monitors (potentially) – traffic to and from the host – OS API calls – system logs • Adds to processing load on the host, so host must be able to support the extra load Spring 2005 © 2000-2005, Richard A. Stanley EE579T/11 #20

Network-based

• NIDS sensors placed on network backbone – Can view only packet traffic passing by, much like a classic passive sniffer – Does not place processing load on network, but the NIDS platform must be capable of dealing with network traffic speeds • Software can usually handle  100 Mbps • Hardware only 2-3 times faster • If network is faster, looks only at subset of packets Spring 2005 © 2000-2005, Richard A. Stanley EE579T/11 #21

Network Node-based

• Used to inspect intrusions directly into network nodes – Effectively a blending of HIDS and NIDS – Used to protect mission-critical machines – Again, a background process on existing nodes, so node must be able to handle added processing load Spring 2005 © 2000-2005, Richard A. Stanley EE579T/11 #22

Gateway

• In series with network – Often set to block prohibited traffic automatically – Think of it as an in-network firewall with an extended rule set – Must be able to keep up with network load Spring 2005 © 2000-2005, Richard A. Stanley EE579T/11 #23

Intrusion Protection Systems

• Latest trend in IDS technology • Idea is to use what the IDS identifies to change the network rules

ad hoc

IPS Issues

• Attack signatures generally known only

a posteriori

• Heuristic analysis has not worked very well in other venues, such as virus detection • How long to maintain the “new” rules before reverting to the original ones?

Deployment

• Putting in an IDS is a complex and time consuming affair – Typically, start simple and add functionality as you learn more about the network – NIDS tends to see more and load network least – Follow up with HIDS on selected hosts, perhaps NNIDS on critical nodes • Policy has to be in place first Spring 2005 © 2000-2005, Richard A. Stanley EE579T/11 #26

Attack Signatures

• Critical to success of any IDS • Must be maintained, just like virus signatures – You want some visibility into this – Do you want strangers deciding what is an attack on your critical systems?

IDS Deployment

• First, design the IDS sensor and management layout • Next, deploy the IDS – Test the network for normal operation – Test the IDS • Run packaged attacks to see if all are detected • Document performance and repeat test regularly – Tune the IDS Spring 2005 © 2000-2005, Richard A. Stanley EE579T/11 #28

Sampling of IDS Products

• RealSecure: http://www.iss.net/products_services/enterp rise_protection/rsnetwork/sensor.php

IDS Summary

• IDS’s can be useful in monitoring networks for intrusions and policy violations • Up-to-date attack signatures and policy implementations essential • Many types of IDS available, at least one as freeware • Serious potential legal implications • Automated responses to be avoided Spring 2005 © 2000-2005, Richard A. Stanley EE579T/11 #30

Wireless Network Security

• Wireless networks growing at a rapid pace – Gartner Group predicts wireless installations will multiply >7X by 2007 to over 31M • Business drivers – Installation cost and time – Mobility – Flexibility – Operating costs Spring 2005 © 2000-2005, Richard A. Stanley EE579T/11 #31

Wireless Inherently Insecure

• Wired networks contain (or try) signals to a wired path, which must be physically tapped to compromise line security – Possible to physically discover the tap • Wireless networks deliberately broadcast data into space, where it can be intercepted by anyone with proper receiver – Data tap impossible to discover Spring 2005 © 2000-2005, Richard A. Stanley EE579T/11 #32

This Isn’t New News

• Since early days, wireless vendors strove to provide privacy equivalent to that available on the wired network – WEP = wired equivalent privacy – This is not a high standard to meet • They succeeded, but that wasn’t good enough for user requirements Spring 2005 © 2000-2005, Richard A. Stanley EE579T/11 #33

Wireless Security Issues

• How does a wireless network work?

• How can you “join up?” • What about the encryption?

• Can it

really

be secure?

How It Works

• Clients send probes • Access points broadcast beacons and, often, their Server Set ID (SSID) • When a client finds an access point with an acceptable signal level and a matching SSID, a connection is established • Many networks are built precisely to facilitate connection by “foreign” users Spring 2005 © 2000-2005, Richard A. Stanley EE579T/11 #35

Wireless LAN Elements

[AP] [STA]

Origins of WEP

• Marketing and Political Issues: – Developed as part of a wireless LAN research project at Apple Computer, Inc..

– Eavesdropping was perceived as a barrier to market acceptance.

– Apple sells into a worldwide market so solution had to be exportable.

– NSA only allowed 40-bit encryption to be exported.

Origins of WEP (cont.)

• Technical Issues: – Eavesdropping on wireless link => privacy and authentication problems.

– Multiple network protocols (in 1993) => solution required at data link layer.

– Data link layer is “best effort” => crypto-state (other than shared key) must accompany each frame.

WEP Solution

• • Apple had unlimited RC4 license from RSA, Inc.

Method and apparatus for variable overhead cached encryption

, US Patent 5,345,508 applied for 23 Aug 1993, granted 6 Sept 1994.

• Licensed for export in mid-1994.

Initialization Vector (IV) Secret Key Plaintext

WEP Encryption

IV + Seed PRNG RC4() Key Sequence Cache

(MAX_MSG_SZ)

IEEE 802.11’s use of WEP

• IEEE runs by Robert’s Rules; “one man, one vote” • Simple majority required to add text, 75% vote to change text in draft standard • WEP introduced in March 1994 • Strong pushback in committee regarding cost and overhead of encryption • Dilution of proposal; privacy made

optional

WEP Security Problems

• Papers submitted to 802.11 committee highlight the problems with WEP; “Unsafe at any Key Size” presented in October 2000 • 802.11 Task Group I formed to solve WEP security problems • Press gets wind of the issue • Public domain attacks; “war driving” Spring 2005 © 2000-2005, Richard A. Stanley EE579T/11 #42

WEP Security Problems (cont.)

• Passive attacks to decrypt traffic based on statistical analysis • Active ‘known plaintext’ attack to inject new traffic from unauthorized mobile stations • Active attacks to decrypt traffic, based on tricking the access point • Dictionary-building attack; real-time automated decryption of all traffic after a day’s sampling Spring 2005 © 2000-2005, Richard A. Stanley EE579T/11 #43

802.11 Task Group I

• Long term security architecture for 802.11

• Based on 802.1X authentication standard and two new encryption protocols (TKIP and CCMP) – Labeled Robust Security Network (RSN) • Uses Upper Layer Authentication (ULA) protocols outside the scope of 802.11i (e.g. EAP/TLS, PEAP) Spring 2005 © 2000-2005, Richard A. Stanley EE579T/11 #44

Robust Security Network

Includes: • Better key derivation/distribution based on 802.1X

– For TKIP: per message 128 bit key derivation • Improved encryption (TKIP, CCMP) • Stronger keyed Message Integrity Checks – Custom MIC for TKIP with 22 bit effective strength – Strong AES based MIC for CCMP • IV sequencing to control message replay – 44 bits to avoid re-keying (4 bits for QoS) Spring 2005 © 2000-2005, Richard A. Stanley EE579T/11 #45

RSN Data Privacy Protocols

• Temporal Key Integrity Protocol (TKIP) – a cipher suite enhancing the WEP protocol on pre-RSN hardware • Counter Mode/CBC-MAC Protocol – based on AES and Counter-Mode/CBC-MAC (CCM) – Mandatory for RSN compliance Spring 2005 © 2000-2005, Richard A. Stanley EE579T/11 #46

802.1X

• Originally designed as port-based network access control for PPP • Provides support for a centralized management model • Primary encryption keys are unique to each station and generated dynamically • Provides support for strong upper layer authentication Spring 2005 © 2000-2005, Richard A. Stanley EE579T/11 #47

802.1X Architectural Framework

• • Employs Extensible Authentication Protocol (EAP) – EAP built around challenge-response paradigm – operates at network layer = flexibility • Provides transport for ULA protocols – EAP/TLS, PEAP, EAP-TTLS, LEAP Two sets of keys dynamically generated – Session Keys, Group Keys Spring 2005 © 2000-2005, Richard A. Stanley EE579T/11 #48

Authentication and Key Mgmt.

Supplicant

Authenticator

Authentication Server

Uncontrolled Port AS RADIUS EAP EE579T/11 #49 EAP

Existing Solutions & Other Methods

Enter The Wi-Fi Alliance

• Wi-Fi Alliance – nonprofit International association formed in 1999 • 176 member companies as of today • Mission: Certify interoperability of Wireless LAN products based on IEEE 802.11 specification Spring 2005 © 2000-2005, Richard A. Stanley EE579T/11 #51

Wi-Fi Protected Access - WPA

• WPA is a response by the industry to offer strong and immediate security solution that would replace WEP • It is a subset of 802.11i draft standard and is going to maintain forward compatibility • Main idea - “Bring what is ready now to the market” • Increases the level of security for Wireless LAN • It is a standards-based, interoperable security specification Spring 2005 © 2000-2005, Richard A. Stanley EE579T/11 #52

WPA

• Provides user authentication – Central authentication server (like RADIUS) – Via 802.1x and EAP • Improves data encryption – Temporal Key Integrity Protocol (TKIP) • Eventually will support full 802.11i compliance Spring 2005 © 2000-2005, Richard A. Stanley EE579T/11 #53

802.11i Status?

• Many devices fielded since 2003 have silicon implementations in them to support full 802.11i

NetStumbler

Exploitation Tools

• Wardriving: http://www.wardriving.com/ • Warchalking: http://www.warchalking.org/ • Airsnort: http://airsnort.shmoo.com/ • WEPCrack: http://wepcrack.sourceforge.net/ What other little “gifts” await us?

Best Practice for now

• WEP is better than nothing; change keys often • Physical placement of Access Points • Upgrade firmware and drivers on APs and Wireless Cards as they are released • VPN (treat wireless users as you would dial-in users) • Check for 802.1x support before buying Spring 2005 © 2000-2005, Richard A. Stanley EE579T/11 #57

Wireless Security Summary

• It’s a problem, owing to the nature of wireless transmission • So far, security implementations have left a lot to be desired • Project presentations will provide added details • Growth is explosive, both in legitimate and illegitimate wireless activity Spring 2005 © 2000-2005, Richard A. Stanley EE579T/11 #58