Transcript WLAN Security

Wireless LAN Security
Black Hat Briefings
July 12, 2001
Mandy Andress
ArcSec Technologies
Agenda
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Uses
Benefits
Standards
Functionality
Security Issues
Solutions and Implementations
Uses
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Key drivers are mobility and accessibility
Easily change work locations in the office
Internet access at airports, cafes, conferences,
etc.
Benefits
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Increased productivity
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Improved collaboration
No need to reconnect to the network
Ability to work in more areas
Reduced costs
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No need to wire hard-to-reach areas
Standards
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IEEE 802.11
IEEE 802.11b
IEEE 802.11a
IEEE 802.11e
HiperLAN/2
Interoperability
802.11
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Published in June 1997
2.4GHz operating frequency
1 to 2 Mbps throughput
Can choose between frequency hopping or
direct sequence spread modulation
802.11b
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Published in late 1999 as supplement to
802.11
Still operates in 2.4GHz band
Data rates can be as high as 11 Mbps
Only direct sequence modulation is specified
Most widely deployed today
802.11a
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Also published in late 1999 as a supplement to 802.11
Operates in 5GHz band (less RF interference than
2.4GHz range)
Users Orthogonal Frequency Division Multiplexing
(OFDM)
Supports data rates up to 54 Mbps
Currently no products available, expected in fourth
quarter
802.11e
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Currently under development
Working to improve security issues
Extensions to MAC layer, longer keys, and key
management systems
Adds 128-bit AES encryption
HiperLAN/2
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Development led by the European
Telecommunications Standards Institute (ETSI)
Operates in the 5 GHz range, uses OFDM
technology, and support data rates over
50Mbps like 802.11a
Interoperability
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802.11a and 802.11b work on different
frequencies, so little chance for interoperability
Can coexist in one network
HiperLAN/2 is not interoperable with 802.11a
or 802.11b
Functionality
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Basic Configuration
WLAN Communication
WLAN Packet Structure
Basic Configuration
802.11 Communication
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CSMA/CA (Carrier Sense Multiple
Access/Collision Avoidance) instead of
Collision Detection
WLAN adapter cannot send and receive traffic
at the same time on the same channel
Hidden Node Problem
Four-Way Handshake
Hidden Node Problem
Four-Way Handshake
Source
Destination
OSI Model
Application
Presentation
Session
Transport
Network
802.11b
Data Link
802.11 MAC header
Physical
802.11 PLCP header
Ethernet Packet Structure
•14 byte header
•2 addresses
Graphic Source: Network Computing Magazine August 7, 2000
802.11 Packet Structure
•30 byte header
•4 addresses
Graphic Source: Network Computing Magazine August 7, 2000
Ethernet Physical Layer Packet
Structure
•8 byte header (Preamble)
Graphic Source: Network Computing Magazine August 7, 2000
802.11 Physical Layer Packet
Structure
•24 byte header (PLCP, Physical Layer Convergence Protocol)
•Always transferred at 1 Mbps
Graphic Source: Network Computing Magazine August 7, 2000
Security Issues and Solutions
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Sniffing and War Driving
Rogue Networks
Policy Management
MAC Address
SSID
WEP
War Driving
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Default installation allow any wireless NIC to
access the network
Drive around (or walk) and gain access to
wireless networks
Provides direct access behind the firewall
Heard reports of an 8 mile range using a 24dB
gain parabolic dish antenna.
Rogue Networks
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Network users often set up rogue wireless
LANs to simplify their lives
Rarely implement security measures
Network is vulnerable to War Driving and
sniffing and you may not even know it
Policy Management
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Access is binary
Full network access or no network access
Need means of identifying and enforcing
access policies
MAC Address
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Can control access by allowing only defined
MAC addresses to connect to the network
This address can be spoofed
Must compile, maintain, and distribute a list of
valid MAC addresses to each access point
Not a valid solution for public applications
Service Set ID (SSID)
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SSID is the network name for a wireless network
WLAN products common defaults: “101” for 3COM and
“tsunami” for Cisco
Can be required to specifically request the access
point by name (lets SSID act as a password)
The more people that know the SSID, the higher the
likelihood it will be misused.
Changing the SSID requires communicating the
change to all users of the network
Wired Equivalent Privacy (WEP)
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Designed to be computationally efficient, selfsynchronizing, and exportable
Vulnerable to attack
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Passive attacks to decrypt traffic based on statistical analysis
Active attacks to inject new traffic from unauthorized mobile
stations, based on known plaintext
Dictionary-building attack that, after analysis of a day’s worth
of traffic, allows real-time automated decryption of all traffic
All users of a given access point share the same
encryption key
Data headers remain unencrypted so anyone can see
the source and destination of the data stream
WLAN Implementations
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Varies due to organization size and security
concerns
Current technology not ideal for large-scale
deployment and management
Will discuss a few tricks that can help the
process and a few technologies under
development to ease enterprise deployments
Basic WLAN
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Great for small (5-10 users) environments
Use WEP (some vendors provide 128-bit
proprietary solution)
Only allow specific MAC addresses to access
the network
Rotate SSID and WEP keys every 30-60 days
No need to purchase additional hardware or
software.
Basic WLAN Architecture
Secure LAN (SLAN)
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Intent to protect link between wireless client and
(assumed) more secure wired network
Similar to a VPN and provides server authentication,
client authentication, data privacy, and integrity using
per session and per user short life keys
Simpler and more cost efficient than a VPN
Cross-platform support and interoperability, not highly
scaleable, though
Supports Linux and Windows
Open Source (slan.sourceforge.net)
SLAN Architecture
SLAN Steps
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Client/Server Version Handshake
Diffie-Hellman Key Exchange
Server Authentication (public key fingerprint)
Client Authentication (optional) with PAM on
Linux
IP Configuration – IP address pool and adjust
routing table
SLAN Client
Client Application
ie Web Browser
Encrypted Traffic to
SLAN Server
Encrypted Traffic
Plaintext Traffic
SLAN Driver
Physical Driver
Plaintext
Traffic
Encrypted Traffic
User Space Process
Intermediate WLAN
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11-100 users
Can use MAC addresses, WEP and rotate
keys if you want.
Some vendors have limited MAC storage
ability
SLAN also an option
Another solution is to tunnel traffic through a
VPN
Intermediate WLAN Architecture
VPN
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Provides a scaleable authentication and
encryption solution
Does require end user configuration and a
strong knowledge of VPN technology
Users must re-authenticate if roaming between
VPN servers
VPN Architecture
VPN Architecture
Enterprise WLAN
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100+ users
Reconfiguring WEP keys not feasible
Multiple access points and subnets
Possible solutions include VLANs, VPNs,
custom solutions, and 802.1x
VLANs
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Combine wireless networks on one VLAN
segment, even geographically separated
networks.
Use 802.1Q VLAN tagging to create a wireless
subnet and a VPN gateway for authentication
and encryption
VLAN Architecture
Customized Gateway
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Georgia Institute of Technology
Allows students with laptops to log on to the campus
network
Uses VLANs, IP Tables, and a Web browser
No end user configuration required
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User access a web site and enters a userid and password
Gateway runs specialized code authenticating the user with
Kerberos and packet filtering with IPTables, adding the user’s
IP address to the allowed list to provide network access
Gateway Architecture
802.1x
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General-purpose port based network access control
mechanism for 802 technologies
Based on AAA infrastructure (RADIUS)
Also uses Extensible Authentication Protocol (EAP,
RFC 2284)
Can provide dynamic encryption key exchange,
eliminating some of the issues with WEP
Roaming is transparent to the end user
802.1x (cont)
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Could be implemented as early as 2002.
Cisco Aironet 350 supports the draft standard.
Microsoft includes support in Windows XP
802.1x Architecture
Third-Party Products
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NetMotion Wireless authenticates against a
Windows domain and uses better encryption
(3DES) than WEP. Also offers the ability to
remotely disable a wireless network card’s
connection.
Fortress Wireless Link Layer Security (WLLS).
Improves WEP and works with 802.1x.
Enterasys provides proprietary RADIUS
solution similar to 802.1x
Client Considerations
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Cannot forget client security
Distributed Personal Firewalls
Strong end user security policies and
configurations
Laptop Theft Controls
Conclusion
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Wireless LANs very useful and convenient, but
current security state not ideal for sensitive
environments.
Cahners In-Stat group predicts the market for
wireless LANs will be $2.2 billion in 2004, up
from $771 million in 2000.
Growing use and popularity require increased
focus on security
Contact Information
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[email protected]
Presentation available for download at
www.arcsec.com and
www.survivingsecurity.com