Wireless connection is lost when the wireless session times out in Windows 7 or Windows Server 2008 R2

This article describes an issue that occurs when the wireless session times out in Windows 7 Service Pack 1 (SP1) or Windows Server 2008 R2 SP1. A hotfix is available to fix this issue. Before you install this hotfix, see the Prerequisites section.

Symptoms

This issue occurs when a Windows 7-based computer is connected to a wireless network by using the Wi-Fi Protected Access II (WPA2) protocol and the wireless access point (AP) starts a new exchange of WPA2 keys. In the four-way handshake, the Windows 7-based computer sends a Message 2 (M2) with an invalid message integrity check (MIC) and secure bit. 

Note This issue may occur every 12 hours or more frequently, and it takes one minute to regain the network connectivity. 

For more information about this issue, go to the Cisco website.

Cause

This issue occurs because the WPA2 key context is not set correctly before the four-way handshake rekeys. Certain variables are not reset after the previous four-way handshake. This causes the secure bit to be set incorrectly and the stale Pairwise Transient Key (PTK) to be used to calculate the MIC in the M2 key messages. Some (specifically but not limited to Cisco) APs reject the M2 messages because of these errors.

Hotfix information

Important If you install a language pack after you install this hotfix, you must reinstall this hotfix. Therefore, we recommend that you install any language packs that you need before you install this hotfix. For more information, see Add language packs to Windows.


A supported hotfix is available from Microsoft. However, this hotfix is intended to correct only the problem that's described in this article. Apply this hotfix only to systems that are experiencing this specific problem.

If the hotfix is available for download, there's a "Hotfix Download Available" section at the top of this Knowledge Base article. If this section doesn't appear, submit a request to Microsoft Customer Service and Support to get the hotfix.

Note If additional issues occur or if any troubleshooting is required, you might have to create a separate service request. The usual support costs will apply to additional support questions and issues that don't qualify for this specific hotfix. For a complete list of Microsoft Customer Service and Support telephone numbers or to create a separate service request, visit the following Microsoft website: Note The "Hotfix Download Available" form displays the languages for which the hotfix is available. If you don't see your language, it's because a hotfix isn't available for that language.


Prerequisites

To apply this hotfix, install Service Pack 1 in Windows 7 or Windows Server 2008 R2.

Registry information

To use the hotfix in this package, you don't have to make any changes to the registry.

Restart requirement

You may have to restart the computer after you apply this hotfix.

Hotfix replacement information

This hotfix doesn't replace a previously released hotfix.

File Information

The English (United States) version of this software update installs files that have the attributes that are listed in the following tables. The dates and times for these files are listed in Coordinated Universal Time (UTC). Be aware that dates and times for these files on your local computer are displayed in your local time and with your current daylight saving time bias. The dates and times may also change when you perform certain operations on the files.
Windows 7 and Windows Server 2008 R2
Additional file information

Status

Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

References

See the terminology that Microsoft uses to describe software updates.

More Information

What changes we have made to fix this issue

This fix addresses an incorrectly set security flag in the M2 message of the rekey handshake. This in turn produces an incorrectly calculated MIC. Some Cisco APs reject the M2 message because of these errors. The fix sets the M2 flag correctly during a rekey handshake.



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ID articolo: 3094412 - Ultima revisione: 04 nov 2015 - Revisione: 1

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