Vary header is overwritten as "Accept-Encoding" after you enable dynamic content compression in Windows

Symptoms

When you enable dynamic content compression on a computer that is running Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7 Service Pack 1 (SP1), or Windows Server 2008 R2 SP1, a Vary header is overwritten as "Accept-Encoding."

For example, in an .aspx page, you set the Vary header as "User-Agent" by using the following code:

using System; 
using System.Collections.Generic;
using System.Web;
using System.Web.UI;

public partial class _Default : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{

Response.Write("Hello");
Response.AppendHeader("Vary", "User-Agent");

}
}

If dynamic content compression is not enabled, the output information resembles the following:

HTTP/1.1 200 OK
Cache-Control: private
Content-Type: text/html; charset=utf-8
Vary: User-Agent
Server: Microsoft-IIS/7.5
X-AspNet-Version: 4.0.30319
X-Powered-By: ASP.NET
Date: Fri, 07 Dec 2012 03:17:29 GMT
Content-Length: 584
However, if dynamic content compression is enabled, the Vary header is overwritten as "Accept-Encoding," and the output information resembles the following:

HTTP/1.1 200 OK
Cache-Control: private
Content-Type: text/html; charset=utf-8
Content-Encoding: gzip
Vary: Accept-Encoding
Server: Microsoft-IIS/7.5
X-AspNet-Version: 4.0.30319
X-Powered-By: ASP.NET
Date: Fri, 07 Dec 2012 03:18:33 GMT
Content-Length: 572

Resolution

Hotfix information

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

If the hotfix is available for download, there is a "Hotfix Download Available" section at the top of this Knowledge Base article. If this section does not appear, submit a request to Microsoft Customer Service and Support to obtain 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 do not 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 do not see your language, it is because a hotfix is not available for that language.

Prerequisites

To apply this hotfix, you must be running one of the following operating systems:

  • Windows 8.1

  • Windows Server 2012 R2

  • Windows 8

  • Windows Server 2012

  • Windows 7 SP1

  • Windows Server 2008 R2 SP1

For more information about how to obtain a Windows 7 or Windows Server 2008 R2 service pack, click the following article number to view the article in the Microsoft Knowledge Base:

976932Information about Service Pack 1 for Windows 7 and for Windows Server 2008 R2

Registry information

To use the hotfix in this package, you do not have to make any changes to the registry.

Restart requirement

You must restart the computer after you apply this hotfix.

Hotfix replacement information

This hotfix does not replace a previously released hotfix.

The global version of this hotfix installs files that have the attributes that are listed in the following tables. The dates and the times for these files are listed in Coordinated Universal Time (UTC). The dates and the times for these files on your local computer are displayed in your local time together with your current daylight saving time (DST) bias. Additionally, the dates and the times may change when you perform certain operations on the files.


Windows 8.1 and Windows Server 2012 R2 file information notesImportant Windows 8.1 hotfixes and Windows Server 2012 R2 hotfixes are included in the same packages. However, only "Windows 8.1" is listed on the Hotfix Request page. To request the hotfix package that applies to one or both operating systems, select the hotfix that is listed under "Windows 8.1" on the page. Always refer to the "Applies To" section in articles to determine the actual operating system that each hotfix applies to.

  • 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

    6.3.960 0.16 xxx

    Windows 8.1 and Windows Server 2012 R2

    RTM

    GDR

  • The MANIFEST files (.manifest) and the MUM files (.mum) that are installed for each environment are listed separately in the "Additional file information for Windows 8.1 and Windows Server 2012 R2" section. MUM and MANIFEST files, and the associated security catalog (.cat) files, are extremely 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.

For all supported x86-based versions of Windows 8.1

File name

File version

File size

Date

Time

Platform

Compdyn.dll

8.5.9600.16457

30,208

08-Nov-2013

04:26

x86

For all supported x64-based versions of Windows 8.1 and of Windows Server 2012 R2

File name

File version

File size

Date

Time

Platform

Compdyn.dll

8.5.9600.16457

42,496

08-Nov-2013

05:00

x64

Compdyn.dll

8.5.9600.16457

30,208

08-Nov-2013

04:26

x86

Windows 8 and Windows Server 2012 file information notesImportant Windows 8 hotfixes and Windows Server 2012 hotfixes are included in the same packages. However, only "Windows 8" is listed on the Hotfix Request page. To request the hotfix package that applies to one or both operating systems, select the hotfix that is listed under "Windows 8" on the page. Always refer to the "Applies To" section in articles to determine the actual operating system that each hotfix applies to.

  • 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

    6.2.920 0.20 xxx

    Windows 8 and Windows Server 2012

    RTM

    LDR

  • The MANIFEST files (.manifest) and the MUM files (.mum) that are installed for each environment are listed separately in the "Additional file information for Windows 8 and Windows Server 2012" section. MUM and MANIFEST files, and the associated security catalog (.cat) files, are extremely 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.

For all supported x86-based versions of Windows 8

File name

File version

File size

Date

Time

Platform

Compdyn.dll

8.0.9200.20869

29,184

04-Nov-2013

23:32

x86

For all supported x64-based versions of Windows 8 and of Windows Server 2012

File name

File version

File size

Date

Time

Platform

Compdyn.dll

8.0.9200.20869

43,008

04-Nov-2013

23:35

x64

Compdyn.dll

8.0.9200.20869

29,184

04-Nov-2013

23:32

x86

Windows 7 and Windows Server 2008 R2 file information notes
Important Windows 7 hotfixes and Windows Server 2008 R2 hotfixes are included in the same packages. However, hotfixes on the Hotfix Request page are listed under both operating systems. To request the hotfix package that applies to one or both operating systems, select the hotfix that is listed under "Windows 7/Windows Server 2008 R2" on the page. Always refer to the "Applies To" section in articles to determine the actual operating system that each hotfix applies to.

  • The files that apply to a specific product, SR_Level (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
    1.22xxx

    Windows 7 and Windows Server 2008 R2

    SP1

    LDR

  • The MANIFEST files (.manifest) and the MUM files (.mum) that are installed for each environment are listed separately in the "Additional file information for Windows 7 and for Windows Server 2008 R2" section. MUM and MANIFEST files, and the associated security catalog (.cat) files, are extremely important to maintaining the state of the updated component. The security catalog files, for which the attributes are not listed, are signed with a Microsoft digital signature.

For all supported x86-based versions of Windows 7

File name

File version

File size

Date

Time

Platform

Compdyn.dll

7.5.7601.22502

42,496

05-Nov-2013

09:26

x86

For all supported x64-based versions of Windows 7 and of Windows Server 2008 R2

File name

File version

File size

Date

Time

Platform

Compdyn.dll

7.5.7601.22502

46,080

05-Nov-2013

10:47

x64

Compdyn.dll

7.5.7601.22502

42,496

05-Nov-2013

09:26

x86

For all supported IA-64-based versions of Windows Server 2008 R2

File name

File version

File size

Date

Time

Platform

Compdyn.dll

7.5.7601.22502

89,600

05-Nov-2013

09:45

IA-64

Compdyn.dll

7.5.7601.22502

42,496

05-Nov-2013

09:26

x86




Workaround

To work around the issue, write two HTTP modules to listen on the RQ_SEND_RESPONSE event notification to add back the original Vary header value. One HTTP module is used to store the original Vary header value before the compression, and the other HTTP module is used to restore the Vary header value after the compression.

Status

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

More Information

For more information about software update terminology, click the following article number to view the article in the Microsoft Knowledge Base:

824684 Description of the standard terminology that is used to describe Microsoft software updates

Additional file information for Windows 8.1 and Windows Server 2012 R2

Additional files for all supported x86-based versions of Windows 8.1

File property

Value

File name

X86_67e665de430797e566b34074602255b9_31bf3856ad364e35_6.3.9600.16457_none_817c65c742e97645.manifest

File version

Not applicable

File size

722

Date (UTC)

08-Nov-2013

Time (UTC)

20:16

File name

X86_microsoft-windows-i..siondynamicbinaries_31bf3856ad364e35_6.3.9600.16457_none_1cd3de6c4b42c0c9.manifest

File version

Not applicable

File size

3,065

Date (UTC)

08-Nov-2013

Time (UTC)

08:42

Additional files for all supported x64-based versions of Windows 8.1 and of Windows Server 2012 R2

File property

Value

File name

Amd64_0ca9258cb95c7a69c528da655645a3bf_31bf3856ad364e35_6.3.9600.16457_none_aa7c672a8e052e6b.manifest

File version

Not applicable

File size

1,094

Date (UTC)

08-Nov-2013

Time (UTC)

20:16

File name

Amd64_microsoft-windows-i..siondynamicbinaries_31bf3856ad364e35_6.3.9600.16457_none_78f279f003a031ff.manifest

File version

Not applicable

File size

3,071

Date (UTC)

08-Nov-2013

Time (UTC)

10:25

File name

Wow64_microsoft-windows-i..siondynamicbinaries_31bf3856ad364e35_6.3.9600.16457_none_834724423800f3fa.manifest

File version

Not applicable

File size

3,071

Date (UTC)

08-Nov-2013

Time (UTC)

08:40

Additional file information for Windows 8 and Windows Server 2012

Additional files for all supported x86-based versions of Windows 8

File property

Value

File name

X86_dfdf42e825e8ebea29f5c8dcd62c3032_31bf3856ad364e35_6.2.9200.20869_none_d33717971ef9d0d2.manifest

File version

Not applicable

File size

722

Date (UTC)

05-Nov-2013

Time (UTC)

20:32

File name

X86_microsoft-windows-i..siondynamicbinaries_31bf3856ad364e35_6.2.9200.20869_none_855ff8eb1a33d62a.manifest

File version

Not applicable

File size

3,065

Date (UTC)

05-Nov-2013

Time (UTC)

00:08

Additional files for all supported x64-based versions of Windows 8 and of Windows Server 2012

File property

Value

File name

Amd64_ddba2377cd28a9a557124c3b98ea1749_31bf3856ad364e35_6.2.9200.20869_none_17199fe1b4059dbb.manifest

File version

Not applicable

File size

1,094

Date (UTC)

05-Nov-2013

Time (UTC)

20:35

File name

Amd64_microsoft-windows-i..siondynamicbinaries_31bf3856ad364e35_6.2.9200.20869_none_e17e946ed2914760.manifest

File version

Not applicable

File size

3,071

Date (UTC)

05-Nov-2013

Time (UTC)

02:53

File name

Wow64_microsoft-windows-i..siondynamicbinaries_31bf3856ad364e35_6.2.9200.20869_none_ebd33ec106f2095b.manifest

File version

Not applicable

File size

3,071

Date (UTC)

04-Nov-2013

Time (UTC)

23:53

Additional file information for Windows 7 and for Windows Server 2008 R2

Additional files for all supported x86-based versions of Windows 7

File property

Value

File name

X86_043ce6947c70b1bbf49e07650c6f34b3_31bf3856ad364e35_6.1.7601.22502_none_165a2ac799bbbfc0.manifest

File version

Not applicable

File size

722

Date (UTC)

05-Nov-2013

Time (UTC)

21:37

File name

X86_microsoft-windows-i..siondynamicbinaries_31bf3856ad364e35_6.1.7601.22502_none_8aaa64bda71dbce2.manifest

File version

Not applicable

File size

3,369

Date (UTC)

05-Nov-2013

Time (UTC)

10:41

Additional files for all supported x64-based versions of Windows 7 and of Windows Server 2008 R2

File property

Value

File name

Amd64_4d649c0e269c7f9981d93b8405047df9_31bf3856ad364e35_6.1.7601.22502_none_ac410899baedf697.manifest

File version

Not applicable

File size

1,094

Date (UTC)

05-Nov-2013

Time (UTC)

21:37

File name

Amd64_microsoft-windows-i..siondynamicbinaries_31bf3856ad364e35_6.1.7601.22502_none_e6c900415f7b2e18.manifest

File version

Not applicable

File size

3,375

Date (UTC)

05-Nov-2013

Time (UTC)

11:19

File name

Wow64_microsoft-windows-i..siondynamicbinaries_31bf3856ad364e35_6.1.7601.22502_none_f11daa9393dbf013.manifest

File version

Not applicable

File size

3,032

Date (UTC)

05-Nov-2013

Time (UTC)

10:08

Additional files for all supported IA-64-based versions of Windows Server 2008 R2

File property

Value

File name

Ia64_fcb8e1a061ef3157c77af37aed6898b2_31bf3856ad364e35_6.1.7601.22502_none_04cd0e8ffd12b0da.manifest

File version

Not applicable

File size

1,092

Date (UTC)

05-Nov-2013

Time (UTC)

21:37

File name

Ia64_microsoft-windows-i..siondynamicbinaries_31bf3856ad364e35_6.1.7601.22502_none_8aac08b3a71bc5de.manifest

File version

Not applicable

File size

3,372

Date (UTC)

05-Nov-2013

Time (UTC)

10:24

File name

Wow64_microsoft-windows-i..siondynamicbinaries_31bf3856ad364e35_6.1.7601.22502_none_f11daa9393dbf013.manifest

File version

Not applicable

File size

3,032

Date (UTC)

05-Nov-2013

Time (UTC)

10:08


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