sa_05.txt

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NSFOCUS Security Advisory(SA2000-05)  
Topic£º Microsoft Windows 9x NETBIOS password verification  
vulnerability  
Release Date£º August 24, 2000  
Affected System£º  
================  
- Microsoft Windows 95  
- Microsoft Windows 98  
- Microsoft Windows 98 Second Edition  
Non-affected System£º  
====================  
- Windows NT 4.0  
- Windows 2000  
Impact:  
==========  
A vulnerability exists in the password verification scheme utilized by  
Microsoft Windows 9x NETBIOS protocol implementation. This  
vulnerability will allow any user to access the Windows 9x file shared  
service with password protection. Attacker don't have to know the  
share password.  
Description£º  
=============  
You can set password to protect Microsoft Windows 9x system's shared  
resources. But a vulnerability exists in the password verification  
scheme utilized by Microsoft Windows 9x NETBIOS protocol  
implementation. To verify the password, the length of the password  
depends on the length of the data sent from client to server. That is,  
if a client set the length of password to be 1 byte and send the  
packet to server, the server will only compare it with the first byte  
of the shared password, and if consistent, verification process is  
done. All an attacker need to do is to guess and try the first byte of  
password in the victim .  
Windows 9x remote management system is also affected cause it adopts  
the same shared password authentication method.  
Workaround£º  
=========  
Close Microsoft file shared service.  
Microsoft has been informed.  
DISCLAIMS:  
==========  
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INFORMATION IS PROVIDED THAT THE ADVISORY IS NOT MODIFIED IN ANY WAY.  
©Coypright 1999-2000 NSFOCUS. All Rights Reserved. Terms of use.  
NSFOCUS Security Team <[email protected]>  
NSFOCUS INFORMATION TECHNOLOGY CO.,LTD  
(http://www.nsfocus.com)  
  
©Copyright 2000 NSFOCUS Information Technology Co.,Ltd. All Rights  
Reserved.  
Contact:[email protected]   
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