October 13, 2020-KB4578974 Cumulative Update for .NET Framework 3.5 and 4.8 for Windows 10, version 1903, Windows Server, version 1903, Windows 10, version 1909, and Windows Server, version 1909

Applies to: .NET Framework

Summary


An information disclosure vulnerability exists when the .NET Framework improperly handles objects in memory. An attacker who successfully exploited the vulnerability could disclose contents of an affected system's memory. To exploit the vulnerability, an authenticated attacker would need to run a specially crafted application. The update addresses the vulnerability by correcting how the .NET Framework handles objects in memory.

To learn more about the vulnerabilities, go to the following Common Vulnerabilities and Exposures (CVE).

Known issues in this update


ASP.Net applications fail during precompilation with error message

Symptoms
After you apply this October 13, 2020 Security and Quality Rollup for .NET Framework 4.8, some ASP.Net applications fail during precompilation. The error message that you receive will likely contain the words “Error ASPCONFIG.”

Cause
An invalid configuration state in either the “sessionState,” “anonymouseIdentification,” or “authentication/forms” sections of “System.web” configuration. This might occur during build-and-publish routines if configuration transformations leave the Web.config file in an intermediate state for precompilation.

Workaround
Customers who observe new unexpected failures or functional issues can implement an application setting by adding (or merging) the following code to the application configuration file. Setting either “true” or “false” will avoid the issue. However, we recommend that you set this value to “true” for sites that do not rely on cookieless features.

<?xml version="1.0" encoding="utf-8" ?><configuration>      <appSettings>          <add key=”aspnet:DisableAppPathModifier” value=”true” />     </appSettings></configuration>

ASP.Net applications may not deliver cookieless tokens in the URI

Symptoms
After you apply this October 1, 2020 Security and Quality Rollup for .NET Framework 4.8, some ASP.Net applications may not deliver cookieless tokens in the URI, possibly resulting in 302-redirect loops or lost or missing session state.

Cause
The ASP.Net features for Session State, Anonymous Identification, and Forms Authentication all rely on issuing tokens to a web client, and they all allow the option for those tokens to be delivered in a cookie or embedded in the URI for clients that don’t support cookies. The URI-embedding has long been an insecure and disrecommended practice and this KB quietly disables issuing tokens in URI’s unless one of these three features explicitly requests a cookie mode of “UseUri” in configuration. Configurations that specify “AutoDetect” or “UseDeviceProfile” may inadvertently result in attempted and failed embedding of these tokens in the URI.

Workaround
Customers who observe new unexpected behavior are recommended to change all three cookieless settings to “UseCookies” if possible.

<?xml version="1.0" encoding="utf-8" ?><configuration>     <system.web>          <anonymousidentification cookieless="UseCookies" />          <sessionState cookieless="UseCookies" />          <authentication>               <forms cookieless="UseCookies" />          </authentication>     </system.web></configuation>

If an application absolutely must continue using URI-embedded tokens and can do so safely, then they can be re-enabled with the following appSeting. But again, it is highly recommended to move away from embedding these tokens in URI’s.

<?xml version="1.0" encoding="utf-8" ?><configuration>     <appSettings>          <add key="aspnet:DisableAppPathModifier" value="false" />     </appSettings></configuation>

 

How to get this update


Install this update

Release Channel Available Next Step
Windows Update and Microsoft Update Yes None. This update will be downloaded and installed automatically from Windows Update.
Microsoft Update Catalog Yes To get the standalone package for this update, go to the Microsoft Update Catalog website.
Windows Server Update Services (WSUS) Yes

This update will automatically sync with WSUS if you configure Products and Classifications as follows:

Product:Windows 10, version 1903, Windows Server, version 1903, Windows 10, version 1909, and Windows Server, version 1909

Classification: Security Updates

File information

For a list of the files that are provided in this update, download the file information for cumulative update .

Information about protection and security