This article describes an issue that blocks communication over a TCP loopback path for applications in Windows 8.1, Windows RT 8.1, or Windows Server 2012 R2. An update is available to fix this issue. Before you install this update, see the Prerequisites section.
When this issue occurs, the loopback TCP packets fall from a fast path to a slow path and are then dropped.
This issue occurs because of an incorrect checksum.
Hotfix informationImportant 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.
PrerequisitesTo apply this hotfix, install update 2919355 in Windows 8.1 or Windows Server 2012 R2.
Registry informationTo use the hotfix in this package, you don't have to make any changes to the registry.
Restart requirementYou may have to restart the computer after you apply this hotfix.
Hotfix replacement informationThis hotfix doesn't replace a previously released hotfix.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
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.