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:

http://support.microsoft.com/contactus/?ws=supportNote 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.

Notes

  • The files that apply to a specific product, milestone (RTM, SPn), and service branch (LDR, GDR) can be identified by examining the file version numbers as shown in the following table:

    Version

    Product

    Milestone

    Service branch

    6.1.760 1.23 xxx

    Windows 7 or Windows Server 2008 R2

    SP1

    LDR

  • GDR service branches contain only those fixes that are widely released to address widespread, critical issues. LDR service branches contain hotfixes in addition to widely released fixes.

  • The MANIFEST files (.manifest) and the MUM files (.mum) that are installed for each environment are listed in the "Additional file information" section. MUM, MANIFEST, and the associated security catalog (.cat) files, are very important to maintain the state of the updated components. The security catalog files, for which the attributes are not listed, are signed with a Microsoft digital signature.

x64 Windows 7 and Windows Server 2008 R2

File name

File version

File size

Date

Time

Platform

Nwifi.sys

6.1.7601.23207

324,096

11-Sep-2015

17:20

x64

x86 Windows 7

File name

File version

File size

Date

Time

Platform

Nwifi.sys

6.1.7601.23207

270,848

11-Sep-2015

17:02

x86


x64 Windows 7 and Windows Server 2008 R2

File property

Value

File name

Amd64_87bc8280f965997a845adad7cf39a6ab_31bf3856ad364e35_6.1.7601.23207_none_1ab274d11e2d1647.manifest

File version

Not applicable

File size

704

Date (UTC)

11-Sep-2015

Time (UTC)

21:24

Platform

Not applicable

File name

Amd64_microsoft-windows-native-80211_31bf3856ad364e35_6.1.7601.23207_none_adc5e6ecbea51f05.manifest

File version

Not applicable

File size

65,699

Date (UTC)

11-Sep-2015

Time (UTC)

18:48

Platform

Not applicable

File name

Update.mum

File version

Not applicable

File size

1,843

Date (UTC)

11-Sep-2015

Time (UTC)

21:24

Platform

Not applicable

x86 Windows 7

File property

Value

File name

Update.mum

File version

Not applicable

File size

1,625

Date (UTC)

11-Sep-2015

Time (UTC)

21:24

Platform

Not applicable

File name

X86_532181f6d9549b37471d0be27cd1ccde_31bf3856ad364e35_6.1.7601.23207_none_91932b15bdebf270.manifest

File version

Not applicable

File size

700

Date (UTC)

11-Sep-2015

Time (UTC)

21:24

Platform

Not applicable

File name

X86_microsoft-windows-native-80211_31bf3856ad364e35_6.1.7601.23207_none_51a74b690647adcf.manifest

File version

Not applicable

File size

65,695

Date (UTC)

11-Sep-2015

Time (UTC)

18:29

Platform

Not applicable


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.

The third-party products that this article discusses are manufactured by companies that are independent of Microsoft. Microsoft makes no warranty, implied or otherwise, about the performance or reliability of these products.

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