[SNS Advisory No.60 rev.2] Windows XP Disclosure of Registered AP Information

["snsadv () lac co jp" <snsadv () lac co jp>]

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SNS Advisory No.60
Windows XP Disclosure of Registered AP Information

Problem first discovered: 30 Aug 2002
Published: 4 Dec 2002
Last revised: 24 Dec 2002
http://www.lac.co.jp/security/english/snsadv_e/60_e.html
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Overview:
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  Windows XP's wireless LAN feature may disclose registered access points
  information.

  Packets encrypted with WEP could be sent out even if the radio wave of
  the original access point does not propagate well.

  There is a risk that the list of SSID values assigned to registered
  access points and the packets encrypted with WEP may be intercepted and
  decrypted.  

Problem Description:
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  Windows XP machines utilizing wireless LAN automatically search for
  available access points. If not found, requests are continuously sent for
  already registered access points available until connection is achieved. 

  If an access point with the same SSID as of an access point already
  configured for XP is installed, Windows XP will recognize it as the same
  access point.  Windows XP will then encrypt packets with WEP and start
  transmission.  

  Information regarding registered SSIDs can be obtained from available
  inquiry packets by using a packet monitoring tool for wireless LAN.

  Additionally, packets encrypted with WEP of any registered access point
  for Windows XP machines can also be intercepted by establishing an access
  point with the same SSID. 

  As the functions to search for available access points and to send
  inquiry requests are always enabled, Windows XP machines using wireless 
  LAN feature will leak SSID information of registered access points if
  they cannot establish a connection with an available access point.

  In addition, WEP is susceptible to some already known vulnerabilities.
  Data encrypted with 40-bit keys can be decrypted through brute force
  attacks in a short period of time.  In the case of 104-bit encryption
  use, it has been reported that data can be decrypted in approximately two
  weeks.

  Consequently, sending out packets encrypted with WEP is not a recommended
  security practice in an environment where the original access points are
  not available.

  Refer to the following URL for explanatory figures: 
    http://www.lac.co.jp/security/english/snsadv_e/60_e.html

Solution:
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  Disable the wireless LAN function of Windows XP and use drivers made from
  third-parties that are not susceptible to the problem described above.

Discovered by:
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  Nobuo Miwa  n-miwa () lac co jp

Vendor Status:
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  This issue was reported to Security Response Team of Microsoft Asia
  Limited on August 30th, 2002 and we have been discussing the possibility
  of changing the "specification" that was reported in this Advisory. 
  However, because the specification of 802.11b wireless is not maintained
  by Microsoft, they can not change the specification.

Comment from Microsoft:
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    This is not an issue that occurs exclusively on Windows XP, rather it
    is an issue with the IEEE 802.11b specification.  Implementing
    IEEE 802.11b to conform to its Wireless Standard and sending Associate
    Requests is not specified by Microsoft. 

Acknowledgements:
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  Security Response Team of Microsoft Asia Limited

Revision History:
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  4 Dec 2002  : * Initial release
 24 Dec 2002  : * Updated "Vendor Status" section
                * Added Comment from Microsoft

Disclaimer:
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  All information in these advisories are subject to change without any 
  advanced notices neither mutual consensus, and each of them is released 
  as it is. LAC Co.,Ltd. is not responsible for any risks of occurrences 
  caused by applying those information.

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