Notified: August 07, 2003 Updated: May 20, 2004
Status
Affected
Vendor Statement
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Cisco Security Notice: Dictionary Attack on Cisco LEAP Vulnerability
Revision 2.0
Last Updated 2004 April 12 1600 UTC (GMT)
For Public Release 2003 August 03 1600 UTC (GMT)
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Contents
Summary
Details
Workarounds
Status of This Notice: Final
Revision History
Cisco Security Procedures
Related Information
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Summary
Cisco LEAP is a mutual authentication algorithm that supports dynamic
derivation of session keys. With Cisco LEAP, mutual authentication relies
on a shared secret, the user's logon password-which is known by the client
and the network, and is used to respond to challenges between the user and
the Remote Authentication Dial-In User Service (RADIUS) server.
As with most password-based authentication algorithms, Cisco LEAP is
vulnerable to dictionary attacks.
Cisco has now announced the availability of EAP-Flexible Authentication
via Secure Tunneling (EAP-FAST) for users who wish to deploy an 802.1X
Extensible Authentication Protocol (EAP) type that does not require
digital certificates and is not vulnerable to dictionary attacks.
This notice will be posted at
http://www.cisco.com/warp/public/707/cisco-sn-20030802-leap.shtml.
Details
At DEFCON, on August 3, 2003, a presentation by Joshua Wright explored
mechanisms that could make it easier for someone to write a tool to launch
an offline dictionary attack on password-based authentications that
leverage Microsoft MS-CHAP, such as Cisco LEAP. The source code of the
dictionary attack tool called "asleap" was released on April 6, 2004.
During a dictionary attack, variations of passwords are used to compromise
a user's authentication credentials. Most password-based authentication
algorithms are vulnerable to dictionary attacks in the absence of a strong
password policy.
Cisco developed EAP-FAST for users who wish to deploy an 802.1X EAP type
that does not require digital certificates and is not vulnerable to
dictionary attacks.
Workarounds
Creating a strong password policy is the most effective way to mitigate
against dictionary attacks. This includes using strong passwords and
periodically expiring passwords. Cisco recommends that customers review
their security policies and incorporate the best practices outlined in the
802.11 Wireless LAN Security White Paper -
http://www.cisco.com/warp/public/cc/pd/witc/ao1200ap/prodlit/wswpf_wp.htm
(refer to section 5.2 "Cisco LEAP Deployment").
Users could migrate to another EAP type like EAP-FAST, PEAP or EAP-TLS
whose authentication methods are not susceptible to dictionary attacks.
* EAP-FAST is an authentication protocol that creates a secure tunnel
without using certificates.
* PEAP is a hybrid authentication protocol that creates a secured TLS
tunnel between the WLAN user and the RADIUS server to authenticate the
user to the network. This requires certificate and public key
infrastructure (PKI) management on both RADIUS servers and WLAN
clients.
* EAP-TLS uses pre-issued digital certificates to authenticate a user to
the network. This requires certificate and PKI management on both
RADIUS servers and WLAN clients.
Status of This Notice: Final
This is a final notice. Although Cisco cannot guarantee the accuracy of
all statements in this notice, all of the facts have been checked to the
best of our ability. Cisco does not anticipate issuing updated versions of
this notice unless there is some material change in the facts. Should
there be a significant change in the facts, Cisco may update this notice.
A stand-alone copy or paraphrase of the text of this security notice that
omits the distribution URL in the following section is an uncontrolled
copy, and may lack important information or contain factual errors.
Revision History
+------------------------------------------+
|Revision 2.0|2004-April-12 |Announcing |
| | |EAP-FAST. |
|------------+--------------+--------------|
|Revision 1.0|2003-August-02|Initial |
| | |release. |
+------------------------------------------+
Cisco Security Procedures
Complete information on reporting security vulnerabilities in Cisco
products, obtaining assistance with security incidents, and registering to
receive security information from Cisco, is available on Cisco's worldwide
website at
http://www.cisco.com/warp/public/707/sec_incident_response.shtml. This
includes instructions for press inquiries regarding Cisco security
notices. All Cisco security advisories are available at
http://www.cisco.com/go/psirt.
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Related Information
* EAP-FAST IETF Draft -
http://www.ietf.org/internet-drafts/draft-cam-winget-eap-fast-00.txt
* EAP-FAST FAQ -
http://www.cisco.com/en/US/products/hw/wireless/ps430/products_qanda_item09186a00802030dc.shtml.
* Read more about Cisco Response to Dictionary Attacks on Cisco LEAP -
http://www.cisco.com/en/US/products/hw/wireless/ps430/prod_bulletin09186a00801cc901.html.
* SAFE Architecture White Paper on Wireless LAN Security (first
published in December 2001) -
http://www.cisco.com/warp/public/cc/so/cuso/epso/sqfr/safwl_wp.htm
(see the section on "Standard EAP with TKIP WLAN Design").
* Information on other authentication types such as Protected Extensible
Authentication Protocol (PEAP), Extensible Authentication Protocol
Transport Layer Security (EAP/TLS), and their deployment information -
http://www.cisco.com/warp/public/707/cisco-sn-20030802-leap.shtml.
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All contents are Copyright (c) 1992-2004 Cisco Systems, Inc. All rights
reserved. Important Notices and Privacy Statement.
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Vendor Information
The vendor has not provided us with any further information regarding this vulnerability.
Addendum
The CERT/CC has no additional comments at this time.
If you have feedback, comments, or additional information about this vulnerability, please send us email.