July 9, 2024-KB5041018 Cumulative Update for .NET Framework 3.5, 4.8 and 4.8.1 for Windows 10 Version 21H2

Breaking change details

The .NET Framework servicing update released on July 2024 security and quality rollup - .NET Framework contains a security fix addressed an elevation of privilege vulnerability detailed in CVE 2024-38081. The fix changed System.IO.Path.GetTempPath method return value. If windows version exposes the GetTempPath2 Win32 API, this method invokes that API and returns the resolved path. See the Remarks section of the GetTempPath2 documentation for more information on how this resolution is performed, including how to control the return value through the use of environment variables. The GetTempPath2 API may not be available on all versions of Windows.

An observable difference between the GetTempPath and GetTempPath2 Win32 APIs is that they return different values for SYSTEM and non-SYSTEM processes. When calling this function from a process running as SYSTEM it will return the path %WINDIR%\SystemTemp, which is inaccessible to non-SYSTEM processes. This return value for SYSTEM processes cannot be overridden by environment variables. For non-SYSTEM processes, GetTempPath2 will behave the same as GetTempPath, respecting the same environment variables to override the return value.

In some scenarios it may be possible to redirect the Temp folder to a different folder using environment variables or other means. Please refer to the official documentation for the GetTempPath2 Win32 API for the most up to date information on this behavior.

Please reference to the System.IO.Path.GetTempPath API for more information.

Temporary workaround

⚠️ Warning: The opt-out will disable the security fix for the elevation of privilege vulnerability detailed in CVE 2024-38081. The opt-out is only for temporary workaround if you're sure that the software is running in secure environments. Microsoft does not recommend applying this temporary workaround.

• Option#1: Opt out in a command window by setting the environment variable​​​​​​​

  • COMPlus_Disable_GetTempPath2=true

• Opiton#2: Opt out globally on the machine by creating a system-wide environment variable and rebooting to ensure all processes observe the change. ​​​​​​​​​​​​​​

  • System-wide environment variables can be set by running “sysdm.cpl” from a cmd window, and then navigating to “Advanced -> Environment variables -> System variables -> New”. 

Resolution

The API behavior change is by design to address the elevation of privilege vulnerability. Any affected software or application is expected to make code change to adapt to this new design change.

Release Channel

Available

Next Step

Windows Update and Microsoft Update

Yes

None. This update will be downloaded and installed automatically from Windows Update.

Windows Update for Business

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 operating system update will offer, as applicable, and individual .NET Framework product updates will be installed. For more information about individual .NET Framework product updates see additional information about this update section.

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

Product: Windows 10 Version 21H2

Classification: Security Updates