A Null Session Leak Is Caused by The GetFileAttributes Function on Windows XP Clients

SYMPTOMS

Microsoft Windows NT 4.0-based servers may show many null sessions when those servers are accessed by Windows XP-based clients. You can see the null sessions by typing net session at a command prompt on a Windows NT 4.0-based server.

Also, when you use Windows Explorer to delete a read-only file that is located on an IBM OS/2 Warp4-based server with the HPFS file system, the file may not be deleted and you do not receive any notification that the file-deletion process did not work. Note that this problem does not occur if you click to clear the Display delete confirmation dialog check box in the Recycle Bin Properties dialog box.

This problem may be triggered by services that are running in the Local System context on the Windows XP-based clients. The problem occurs if these services make calls to the GetFileAttributes Win32 function to obtain information about a share on a Windows NT 4.0-based server when the Windows XP-based client views the share in Windows Explorer.

CAUSE

When the null-sessions problem occurs, the Windows XP-based client combines a "Session Setup And X" Server Message Block (SMB) request and a "Tree Connect and X" SMB request into a single SMB request. If this combined request does not succeed, Windows XP does not test to determine which of the two requests did not succeed. Instead, Windows XP always assumes that the "Session Setup And X" request did not succeed, and that no cleanup is required.

If the "Session Setup And X" request succeeds but the "Tree Connect And X" request does not succeed (for example, when a service that is running under the Local System context tries to access a share on the Windows NT 4.0-based server), the client should send a logoff request to remove the session that was created by the "Session Setup And X" request.

RESOLUTION

A supported fix is now available from Microsoft, but it is only intended to correct the problem that is described in this article. Apply it only to computers that are experiencing this specific problem. This fix may receive additional testing. Therefore, if you are not severely affected by this problem, Microsoft recommends that you wait for the next Windows XP service pack that contains this fix.

To resolve this problem immediately, contact Microsoft Product Support Services to obtain the fix. For a complete list of Microsoft Product Support Services phone numbers and information about support costs, visit the following Microsoft Web site:

http://support.microsoft.com/default.aspx?scid=fh;EN-US;CNTACTMS

NOTE: In special cases, charges that are ordinarily incurred for support calls may be canceled if a Microsoft Support Professional determines that a specific update will resolve your problem. The typical support costs will apply to additional support questions and issues that do not qualify for the specific update in question.

The English version of this fix has the file attributes (or later) that are listed in the following table. The dates and times for these files are listed in coordinated universal time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time tool in Control Panel.

Date Time Version Size File name ---------------------------------------------------- 16-Aug-2002 14:43 5.1.2600.56 391,936 Mrxsmb.sys

This hotfix modifies Windows XP to send the two requests separately. Therefore, if the "Session Setup And X" request succeeds but the "Tree Connect And X" request does not succeed, a logoff request is sent to close the session that was created by the "Session Setup And X" request and to prevent the null-session leak.

STATUS

Microsoft has confirmed that this is a problem in the Microsoft products that are listed at the beginning of this article.

APPLIES TO

 © 2006 LBCI Corporation. All rights reserved Eng.Hanna Ata Lahoud