This security update resolves a vulnerability in Microsoft .NET Framework that could allow remote code execution when .NET Framework processes untrusted input. An attacker who successfully exploits this vulnerability in software by using .NET Framework could take control of an affected system. The attacker could then install programs; view, change, or delete data; or create new accounts that have full user rights. Users whose accounts are configured to have fewer user rights on the system could be less affected than users who operate with administrative user rights.
To exploit the vulnerability, an attacker would first have to convince the user to open a malicious document or application.
This security update addresses the vulnerability by correcting how .NET Framework validates untrusted input.
To learn more about this vulnerability, see Microsoft Common Vulnerabilities and Exposures CVE-2018-8421.
- All updates for Windows 8.1, Windows RT 8.1, and Windows Server 2012 R2 require that update KB 2919355 is installed. We recommend that you install update KB 2919355 on your Windows 8.1-based, Windows RT 8.1-based, or Windows Server 2012 R2-based computer so that you receive updates in the future.
- If you install a language pack after you install this update, you must reinstall this update. Therefore, we recommend that you install any language packs that you need before you install this update. For more information, see Add language packs to Windows.
Additional information about this security update
For more information about this security update as it relates to Windows 8.1, Windows RT 8.1, and Windows Server 2012 R2, see the following article in the Microsoft Knowledge Base:
4457920 Security and Quality Rollup updates for .NET Framework 3.5, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, and 4.7.2 for Windows 8.1, RT 8.1, and Server 2012 R2 (KB 4457920)
For more information about this known issue, see the following article in the Microsoft Knowledge Base:
4465015 SharePoint Workflows stop working after you install .NET security updates for CVE-2018-8421
How to obtain and install the update
Method 1: Windows Update
This update is available through Windows Update. When you turn on automatic updating, this update will be downloaded and installed automatically. For more information about how to get security updates automatically, see Windows Update: FAQ.
Method 2: Windows Software Update Services (WSUS)
On your WSUS server, follow these steps:
- Select Start, select Administrative Tools, and then select Microsoft Windows Server Update Services 3.0.
- Expand ComputerName, and then select Action.
- Select Import Updates.
- WSUS opens a browser window in which you may be prompted to install an ActiveX control. Install the ActiveX control to continue.
- After the ActiveX control is installed, you see the Microsoft Update Catalog screen. Type 4457915 in the Search box, and then select Search.
- Locate the .NET Framework packages that match the operating systems, languages, and processors in your environment. Select Add to add them to your basket.
- After you select all the packages that you need, select View Basket.
- To import the packages to your WSUS server, select Import.
- After the packages are imported, select Close to return to WSUS.
The updates are now available for installation through WSUS.
Update deployment information
For deployment details for this security update, go to the following article in the Microsoft Knowledge Base:
20180911 Security update deployment information: September 11, 2018
Update removal information
Note We do not recommend that you remove any security update. To remove this update, use the Programs and Features item in Control Panel.
Update restart information
This update does not require a system restart after you apply it unless files that are being updated are locked or are being used.