This article was previously published under Q165403
This article has been archived. It is offered "as is" and will no longer be updated.
Using a program specifically designed for such a purpose, it may be possible to force a Windows 95-based computer running the Microsoft Client for Microsoft Networks to send a user's logon name and password across the network in a clear-text format, instead of the normal encrypted format. It may then be possible to intercept and read that password using such a program.
When a Windows 95-based computer running the Microsoft Client for Microsoft Networks (which uses the SMB file-sharing protocol) connects to an SMB server, a negotiation takes place to determine which dialect of the SMB protocol will be used for communication. Microsoft Networking clients and servers generally support the ability to use older SMB dialects to support interoperability with older products. Some of these older dialects do not support sending passwords over the network in an encrypted form. When such a dialect is negotiated, passwords are sent over the network in clear-text form.
This issue is resolved by the following updated files for Windows 95:
Vredir.vxd version 4.00.1114 (dated 6/2/97) and later Vnetsup.vxd version 4.00.1112 (dated 6/2/97) and later
To install this update, follow these steps:
Download the Vrdrupd.exe file to an empty folder.
In My Computer or Windows Explorer, double-click the Vrdrupd.exe file you downloaded in step 1.
Follow the instructions on the screen.
The following file is available for download from the Microsoft Download Center:
For additional information about how to download Microsoft Support files, click the following article number to view the article in the Microsoft Knowledge Base:
119591 How to Obtain Microsoft Support Files from Online Services
Microsoft scanned this file for viruses. Microsoft used the most current virus-detection software that was available on the date that the file was posted. The file is stored on security-enhanced servers that help to prevent any unauthorized changes to the file.
The following files are installed by Vrdrupd.exe:
File name Version Date/Time Size Destination folder --------------------------------------------------------------------- Vredir.vxd 4.00.1114 6/2/97 11:14a 156,773 Windows\System Vnetsup.vxd 4.00.1112 6/2/97 11:12a 17,595 Windows\System
With this update installed, connecting to older SMB servers using the Client for Microsoft Networks is no longer possible, because these older servers do not support encryption of passwords sent over the network.
The following SMB servers are known not to support password encryption over the network:
LAN Manager for UNIX (including Hewlett-Packard LM/X)
Samba (unless configured for Challenge/Response password encryption)
For additional information about security in Microsoft products, see the following Microsoft Web site:
138014 File May Be Truncated to Zero Bytes When Copied Onto Itself
136834 Error Copying Read-Only Files to Core SMB Server