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WLAN Security FAQ
From: "Klaus, Chris (ISSAtlanta)" <CKlaus () iss net>
Date: Mon, 8 Oct 2001 13:14:13 -0400

Here is a Wireless LAN Security FAQ, specifically targetting WiFi that I'm
working on.   Hope you find it useful.  

Wireless 802.11b Security FAQ

By Christopher W. Klaus of Internet Security Systems (ISS)
Email: cklaus () iss net

Version 1.1


What is the overview of Wireless LAN 802.11 technology?
What are the major risks?
What are solutions to minimizing WLAN risk?

Recent Updates
Version 1.1
-       Added NetStumbler, WEPCrack tools, Added WEP insecurity paper
-       Added Ecutel, BlueSocket, and NetMotion as WLAN Sec. Products
-       Updated Accuracy of WEP description and made it clear that SSID not
being encrypted.
-       Added Broadcast of SSID turned off can still be circumvented.
-       Added Addtron's default SSID, a popular AP
-       Added War Driving AP maps.
-       Added 802.11 ArpSpoof, a technique used by ISS X-Force Consulting.
-       Added hijacking SSH and SSL connections via wireless.
-       Added 2 X-Force Advisories on Wireless 802.11 flaws

Version 1.0
        - First draft

What is 

Wireless LAN technology standard 802.11b has the strongest momentum to
becoming the main standard for corporate internal wireless LAN networks.
The bandwidth of 802.11b is 11 mbits and operates at 2.4 GHz Frequency.  The
successor of this current 802.11b standard is 802.11a and it is designed to
be faster speed and operate at a different frequency.  While 802.11a
standard and the technology behind it will be in the near distant future,
802.11b is here today and many companies and even individuals are deploying
and using it now.   

As more wireless technology is developed and implemented, the complexity of
the types of attacks will increase, but these appear the standard main
methods used to break and attack wireless systems.  These attacks may be
very similar against other wireless type technologies and is not unique to
802.11b.  By understanding these risks and how to develop security solution
for 802.11b, this will be a good stepping-stone for providing a good secure
solution to any wireless solution.

The AP (access point also known as a base station) is the wireless server
that connects clients to the internal network.  Base stations typically act
as a bridge for the clients.  There is an IP address for management
configuration of the base station.  The base stations typically have an SNMP
agent for remote management.  Some clients like desktops and laptops may
have a SNMP agent running, but not usually.  

        Base stations have become relatively inexpensive, approximately
under $300. The 802.11 client cards for PDAs, laptops, and desktops are
approximately under $100.  Because of inexpensive equipment to get into
wireless, attackers can get easy access to the tools necessary to apply the
attack.  Because of the inexpensive price, within many companies employees
can purchase wireless equipment without approval and deploy this in a rogue
fashion, creating additional risk.

        While this FAQ focuses on the risk issues from a corporate network
perspective, these same issues apply to home networks and telecommuters that
are using wireless.  As the corporate networks are allowing in remote users,
these remote users may be using wireless at their end-point to connect in.
In this case, even if wireless capabilities have not been installed on the
corporate network, they may still be affected by the risk that their remote
employees are using wireless at home or on the road.   

        Airports, hotels, and even coffee shops like Starbucks are deploying
802.11 networks so people can wirelessly browse the Internet with their
laptops.  As these types of networks increase, this will create additional
security risk for the remote user if not properly protected.

Many of the security issues around 802.11b will continue to be an issue with
802.11a, therefore by understanding current issues will help organizations
deal with future issues as well.  This 802.11b security FAQ is broken into 2

        *       Known Risks - What are the major risks that we are aware of
with 802.11b?
        *       Current Security Solutions - What can we do today to protect
802.11b infrastructure?

What are the Known Risks around 802.11b security?

Here is the list of main known security risks with 802.11b.  

        1)      Insertion Attacks 
        2)      Interception and monitoring wireless traffic
        3)      Misconfiguration
        4)      Jamming
        5)      Client to Client Attacks

Insertion Attacks 

        The insertion attacks are based on placing unauthorized devices on
the wireless network without going through a security process and review. 

Plug-in Unauthorized Clients

An attacker tries to connect his wireless client, typically a laptop or PDA,
to a basestation without authorization.  Base stations can be configured to
require a password before clients can access.  If there is no password, an
intruder can connect to the internal network by connecting a client to the
base station.

Plug-in Unauthorized Renegade Base Station
        Many companies may not be aware that internal employees have
deployed wireless capabilities on their network.  An internal employee
wanting to add their own wireless capabilities to the network plugs in their
own base station into the wired intranet.  This is a risk if the base
station has not been properly secured.  This could lead to the previously
described attack of unauthorized clients then gaining access to unauthorized
base stations, allowing intruders into the internal network.  Typically,
companies may need a policy against allowing employees to add wireless base
stations onto the corporate network without requesting permission and going
through a security process.  A sophisticated intruder may physical place a
base station on the victims' network to allow them remote access via

Interception and monitoring wireless traffic

        These interception and monitoring attacks are popular on broadcast
wired networks like Ethernet.  The same principles apply to wireless.

Wireless Sniffer

        An attacker can sniff and capture legitimate traffic.  Many of the
sniffer tools for Ethernet are based on capturing the first part of the
connection session, where the data would typically include the username and
password.  An intruder can masquerade as that user by using this captured
information.  An intruder who monitors the wireless network can apply this
same attack principle on the wireless.

One of the big differences between wireless sniffer attacks and wired
sniffer attacks is that a wired sniffer attack is achieved by remotely
placing a sniffer program on a compromised server and monitor the local
network segment.  This sniffer based attack can happen from anywhere in the
world.  Wireless sniffing requires the attacker to typically be within range
of the wireless traffic.  This is usually around 300 feet range, but
wireless equipment keeps strengthening the signal and pushing this range
further out.  

If an attacker can sniff the wireless traffic, it is possible to inject
false traffic into a connection.  An attacker may be able to issue commands
on behalf of a legitimate user by injecting traffic and hijacking their
victim's session.   

I       Broadcast Monitoring

If a base station is connected to a hub rather than a switch, any network
traffic across that hub can be potentially broadcasted out over the wireless
network.  Because the Ethernet hub broadcasts all data packets to all
connected devices including the wireless base station, an attacker can
monitor sensitive data going over wireless not even intended for any
wireless clients.  

        ArpSpoof Monitoring and Hijacking

Normally, in regards to an AP, the network data traffic on the backbone of a
subnet would be treated similarly like a network switch, thus traffic not
intended for any wireless client would not be sent over the airwaves.  This
could reduce significantly the amount of sensitive data over the wireless

An attacker using the arpspoof technique can trick the network into passing
sensitive data from the backbone of the subnet and route it through the
attacker's wireless client.  This provides the attacker both access to
sensitive data that normally would not be sent over wireless and an
opportunity to hijack TCP sessions. Dsniff is a popular tool that enables
arpspoofing and is available at: http://www.monkey.org/~dugsong/dsniff/

Hijacking SSL (Secure Socket Layer) and SSH (Secure Shell) connections.  

By using arpspoofing technique, an attacker can hijack simple TCP
connections.  There are tools that allow for hijacking SSL and SSH
connections.  Typically, when SSL and SSH connections get hijacked, the only
alert to the end-user is a warning that the credentials of the host and
certificate have changed and ask if you trust the new ones.  Many users
simply accept the new credentials, thus allowing an attacker to succeed. A
reasonable interim measure to prevent the attack is to have users enable
SSH's StrictHostKeyChecking option, and to distribute server key signatures
to mobile clients.  

The Dsniff FAQ explains how to hijack in detail SSH and HTTPS connections:

BaseStation Clone (Evil Twin) intercept traffic

        An attacker can trick legitimate wireless clients to connect to the
attacker's honeypot network by placing an unauthorized base station with a
stronger signal within close proximity of the wireless clients that mimic a
legitimate base station.  This may cause unaware users to attempt to log
into the attacker's honeypot servers.  With false login prompts, the user
unknowingly can give away sensitive data like passwords.      


By default, all the base stations analyzed out of the box from the factory
were configured in the least secure mode possible.  Adding the proper
security configuration was left up as an exercise to the administrator to
lock down.  Unless the administrator of the base station understands the
security risks, most of the base stations will remain at a high risk level.
The analysis of three base station models by the leading 802.11 vendors lead
to many configuration issues that should be audited and assessed by the
organization.  The top three base station vendors analyzed were Cisco,
Lucent, and 3Com.  The security risks identified may change in newer
versions of the 802.11 solution as it is evolving rapidly.  Each vendor had
different implementation security risks, but the underlying issues are the
same and can be applied to other vendors not listed here.

Server Set ID (SSID) 

SSID is a configurable identification that allows clients to communicate to
the appropriate base station.  With proper configuration, only clients that
are configured with the same SSID can communicate with base stations having
the same SSID.  SSID from a security point of view acts as a simple single
shared password between base stations and clients.    

Each of the base station models came with default SSIDs.  Attackers can use
these default SSIDs to attempt to penetrate base stations that are still in
their default configuration.  Here are some default SSIDs:

"tsunami" - Cisco 
"101" - 3Com
"RoamAbout Default Network Name" - Lucent/Cabletron 
"Default SSID"
"Compaq" - Compaq
"WLAN" - Addtron, a popular AP
"intel" - Intel
"linksys" - Linksys

Lucent has Secure Access mode.  This configuration option requires the SSID
of both client and base station to match. By default this security option is
turned off.    In non-secure access mode, clients can connect to the base
station using the configured SSID, a blank SSID, and the SSID configured as

Bruteforce Base Station SSID

Most base stations today are configured with a server set id (SSID) that
acts as a single key or password that is shared with all connecting wireless

An attacker can try to guess the base station SSID by attempting to use a
bruteforce dictionary attack by trying every possible password.  Most
companies and people configure most passwords to be simple to remember and
therefore easy to guess. Once the intruder guesses the SSID, they can gain
access through the base station.

The SSID could be obtained through one of the wireless clients becoming
compromised or an employee resigns knowing the key, there is risk that
anyone with the SSID could still connect to the base station until the SSID
is changed.  If there are many wireless users and clients, it can become
problematic to scale this security solution if the SSID needs to be changed
frequently and all clients and base stations need to reconfigured with an
updated shared single SSID each time.

WEP, the encryption standard for 802.11, only encrypts the data packets not
the 802.11 management packets and the SSID is in the beacon and probe
management messages.  The SSID is not encrypted if WEP is turned on.  The
SSID goes over the air in clear text.  This makes obtaining the SSID easy by
sniffing 802.11 wireless traffic.  

Many APs by default have broadcasting the SSID turned on.  Sniffers
typically will find the SSID in the broadcast beacon packets.  Turning off
the broadcast of SSID in the beacon message (a common practice) does not
prevent getting the SSID; since the SSID is sent in the clear in the probe
message when a client associates to an AP, a sniffer just has to wait for a
valid user to associate to the network to see the SSID.

Wired Equivalent Privacy (WEP)

WEP can be typically configured in 3 possible modes:
        -       No encryption mode
        -       40 bit encryption
        -       128 bit encryption

WEP, by default out of the box, all 3 base station models analyzed have WEP
turned off.  40 bit encryption versus 128 bit encryption provides no added
protection against the known flaw in WEP.

In some base stations, it is optional whether the encryption is enforced.
The WEP encrypted may be turned on, but if it is not enforced, a client
without encryption with the proper SSID can still access that base station.

Attacks against WEP

802.11b standard uses encryption called WEP (Wired Equivalent Privacy).  It
has some known weaknesses in how the encryption is implemented.  

Papers on WEP Insecurities
  Researchers at Berkeley have documented these findings at:

  Using the Fluhrer, Mantin, and Shamir Attack to Break WEP
Using WEP is better than not using it. It at least stops casual sniffers.
Today, there are readily available tools for most attackers to crack the WEP
keys.  Airsnort and others tools take a lot of packets (several million) to
get the WEP key, on most networks this takes longer than most people are
willing to wait.  If the network is very busy, the WEP key can be cracked
and obtained within 15 minutes.

The fix for encryption weakness for the standard is not slated to be
addressed before 2002.  

Because of the WEP weakness, wireless sniffing and hijacking techniques can
work despite the WEP encrypted turned on.

There is the IEEE 802.1X standard which allows network access to be
authenticated and keys to be distributed. This allows access to APs to be
authenticated and WEP keys to be distributed and updated.  More APs are
starting to support this standard.

SNMP community words

Many of the wireless base stations have SNMP (Simple Network Management
Protocol) agents running.  If the community word is not properly configured,
an intruder can read and potentially write sensitive information and data on
the base station.  If SNMP agents are enabled on the wireless clients, the
same risk applies to them as well.  

By default, all three base stations are read accessible by using the
community word, "public".  

By default, the 3com base station has write access by using the community
word, "comcomcom".  Cisco and Lucent/Cabletron require the write community
word to be configured by the user before it is enabled.
SNMP information

With the default of most base stations using the community word "public",
potentially sensitive information can be obtained from the base station.

Configuration Interfaces

Each base station model has its own interfaces for viewing and modifying the
configuration.  Here are the current interface options for each base

        -       Cisco - SNMP, serial, Web, telnet
        -       Lucent / Cabletron - SNMP, serial (no web/telnet)
        -       3Com - SNMP, serial, Web, telnet.

3com base station lacks any access control from the web interfaces for
reading the configuration options.  By connecting to the 3com base station
web interface, it provides SSID on the "system properties menu" display. An
attacker who finds a 3com base station web interface can easily get the

3com base station does require a password on the web interface for write
privileges. The password is the same as the community word for write
privileges, therefore 3com base stations are at risk if deployed using the
default, "comcomcom" as the password. This gives an attacker easy write

Client side security risk

For the clients connecting to the base station, they store sensitive
information for authenticating and communicating to the base station.  If
the client is not properly configured, access to this information is

        -       Cisco client software stores the SSID in the Windows
registry. Cisco stores the WEP key in the firmware, which is difficult to
gain access to.
        -       Lucent/Cabletron client software stores the SSID in the
Windows registry.  The WEP is stored in the Windows registry but it is
encrypted.  The encryption algorithm is not documented.  
        -       3Com client software stores the SSID in the Windows
registry. The WEP key is stored in registry with no encryption.

Windows XP has 802.11 configuration and has a display of the available
SSID's built-in to the OS.


By default, all installations are optimized for the quickest configuration
to get users successful out of the box.  Inversely, by default, the
installations are configured the least secure mode as possible.

From out of the box experience, Cisco was simple and easiest to install.
3Com installation was straight forward out of the box.  And Lucent/Cabletron
had many firmware upgrades which led to confusion on which upgrades to


Denial of service attacks for wired networks are popular.  This same
principle can be applied to wireless traffic, where legitimate traffic gets
jammed because illegitimate traffic overwhelms the frequencies, and
legitimate traffic can not get through.
2.4 GHz Interfering Technology
An attacker with the proper equipment and tools can easily flood the 2.4 GHz
frequency, so that the signal to noise drops so low, that the wireless
network ceases to function.  This can be a risk with even non-malicious
intent as more technologies use the same frequencies and cause blocking.
Cordless phones, baby monitors, and other devices like Bluetooth that
operate on the 2.4 GHz frequency can disrupt a wireless network.

Client to Client Attacks

Two wireless clients can talk directly to each other by-passing the base
station.  Because of this, each client must protect itself from other
Filesharing and other TCP/IP service attacks 

If a wireless client, like a laptop or desktop, is running TCP/IP services
like a web server or file sharing, an attacker can exploit any
misconfigurations or vulnerabilities with another client.

DOS (Denial of Service)

        A wireless client can flood another wirelss client with bogus
packets, creating a denial of service attack.   An attacker and sometimes
employees unintentionally can configure their client to duplicate the IP or
MAC address of another legitimate client causing disruption on the network. 
War Driving Access Point Maps

As people are "War Driving", and locating the APs and recording the GPS
coordinates of the AP location, these AP maps are being shared to any
attacker on the Internet.  If a company has their AP location and
information shared on the Internet, their AP becomes a potential target and
increases their risk.  One of the popular places to upload War Driving AP
maps, is to http://www.netstumbler.com. It includes a visual map and a
database query tool for locating various AP's.

Current Solutions

There are many options that organizations can do today to put proper
security protection around their wireless strategy and technology.

Wireless Security Policy and Architecture Design

Many organization need to develop a wireless security policy to define what
is and what is not allowed with wireless technology.  From a holistic view,
the wireless network should be designed with the proper architecture to
minimize risk.

Treat BaseStations as Untrusted

From an network security architecture, the base stations should be evaluated
and determined if it should be treated as an untrusted device and need to be
quarinteed before the wireless clients can gain access to the internal
network.  The architecture design may include appropriately placing
firewalls, VPNs, IDSes, vulnerability assessments, authentication
requirements between base station and the Intranet.

Base Station Configuration Policy

The wireless policy may want to define the standard security settings for
any 802.11 base station being deployed.  It should cover security issues
like the Server Set ID, WEP keys and encryption, and SNMP community words.

Base Station Discovery

From a wired network search, an organization could identify unknown and
rogue base stations by searching for SNMP agents.  The rogue base stations
are identified as 802.11 devices through SNMP queries for host id.  

Some base stations have a web and telnet interface.  By looking at the
banner strings of these interfaces, this provides another method of
identifying some 802.11 devices.   

An additional means is by using unique TCP/IP attributes like a fingerprint,
it can help identify devices as base stations.  Most TCP/IP implementations
have a unique set of characteristics and many OS fingerprinting technologies
use this method for identifying the OS type.  This concept can be applied to
the base stations.

From a wireless network search, an organization can identify these rogue
base stations by simply setting up a 2.4 GHz sniffer that identifies 802.11
packets in the air.  By looking at the packets, you may find the IP
addresses to help identify which network they are on.  In a densely
populated area with many businesses close together, running a sniffer may
pick up more the intended organization's traffic, but a close neighboring

Base Station Security Assessments

An organization can examine and analyze the base station configuration.  A
security audit and assessment could determine whether the passwords and
community words are still default or easily guessed and if better security
modes have been enabled like encryption.

With router ACLs and firewall rules, an organization can minimize access to
the SNMP agents and other interfaces on the base station.  A security
assessment can determine how widely accessible is the configuration
interfaces to the base stations are allowed to within the organization.

Wireless Client Protection

The wireless clients should be assessed for having the following security
        -       firecell (distributed personal firewalls) - lock down who
can gain access to the client
        -       VPN - adds another layer of encryption and authentication
beyond what 802.11 can provide.
        -       intrusion detection - identify and minimize attacks from
intruders, worms, viruses, Trojans and backdoors.
-       desktop scanning - identify security misconfigurations on the

802.11 Security Products

The WG-1000 Wireless Gateway(tm) offers a single scalable solution to the
security, quality of service (QoS) and management issues facing enterprises
and service providers that deploy wireless LANs based on the IEEE 802.11b
and Bluetooth(tm) standards.

Viatores Secure WLAN edition is different from legacy virtual private
networks (VPNs) in that it maintains VPN and application sessions
uninterrupted with no configuration or re-boot required. 
Viatores combines two advanced protocols for mobility and security to enable
roaming from LANs to WLANs and between WLAN subnets seamlessly and securely.
Application sessions and security tunnels are maintained while the user
moves from one subnet to another. Roaming users can communicate easily with
colleagues, regardless of where they are or how they are connected, because
Viatores maintains a single network address. 

Viatores Secure WLAN edition includes: 
-  Industry-strength secure communication well beyond the WEP standard;
-  Seamless roaming from wired to wireless networks and between different
wireless networks;
-  Support for two-way, peer-to-peer communication;
-  Data confidentiality and integrity, including key exchanges, digital
signatures, and industry-strength encryption; 
-  Option to upgrade to secure and seamless roaming from public networks.

NetMotion Wireless
NetMotion Mobility provides a VPN designed to work with WLAN security.
has an overview of wireless security and how NetMotion Mobility(tm) prevents
unauthorized users from accessing your system and stops eavesdropping,
replay, and other network-level attacks.

802.11 Security Analysis Tools

AirSnort is a wireless LAN (WLAN) tool that recovers encryption keys. It
operates by passively monitoring transmissions, computing the encryption key
when enough packets have been gathered.
AirSnort will work for both 40 or 128 bit encryption.

WEPCrack is a tool that cracks 802.11 WEP encryption keys using the latest
discovered weakness of RC4 key scheduling.

Network Stumbler scans for networks roughly every second and logs all the
networks it runs into--including the real SSIDs, the AP's MAC address, the
best signal-to-noise ratio encountered, and the time you crossed into the
network's space. If you add a GPS receiver to the notebook, it logs the
exact latitude and longitude of the AP. 

Internet Scanner 6.2, the market leading network vulnerability assessment
tool, was the first to assess many 802.11b security checks. 802.11 checks
are in several X-Press Updates (XPU 4.9 and 4.10).

RealSecure 6.0, the market leading IDS, was the first to monitor many
802.11b attacks.  Recommend to make sure you are up to the latest X-Press
Updates.  802.11 checks for IDS were in XPU 3.1. 

About Internet Security System's Wireless 802.11b Solution

ISS offers the comprehensive wireless security solution:

Wireless Security Assessments and Penetration Testing 
Wireless Policy Design and Workshops
Vulnerability Scanning with specific 802.11 configuration checks
Intrusion Detection for Wireless LAN networks 
Wireless 802.11 Security Classes
ISS X-Force Advisories:
  http://xforce.iss.net/alerts/advise83.php WEP Key exposed
  http://xforce.iss.net/alerts/advise84.php 802.11 SNMP Auth. Flaw

Copyright © 2001, Internet Security Systems. All rights reserved.
This document may be redistributed only in its entirety with version date,
authorship notice, and acknowledgements intact. No part of it may be sold
for profit or incorporated in a commercial document without the permission
of the copyright holder. Permission will be granted for complete electronic
copies to be made available as an archive or mirror service on the condition
that the author be notified and that the copy be kept up to date. This
document is provided as is without any express or implied warranty.

Christopher W. Klaus
Founder and CTO
Internet Security Systems (ISS)
6303 Barfield Road
Atlanta, GA 30328
Phone: 404-236-4051 Fax: 404-236-2637
web http://www.iss.net

Internet Security Systems ~ The Power To Protect

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