KB5036621: Cumulative update for .NET Framework, versions 3.5 and 4.8.1, on Windows Server 2022, April 2024. Remote code execution flaw and application slowdowns addressed

For: Windows Server 2022 systems with .NET Framework installed

• A security flaw that could let an attacker run code is addressed.¹
  Addresses CVE-2024-21409, a .NET Framework remote code execution vulnerability.
• A security issue involving an outdated library used by .NET is addressed.²
  Addresses an issue where the version of the OSS zlib library is out of date.
• A security issue in a .NET data-fetching process is addressed.³
  Addresses an issue in the AIA fetching process.

For: Applications using ASP.NET

• A performance slowdown involving an ASP.NET component for handling JavaScript data is addressed.⁴
  Addresses a performance degradation with JavaScriptSerializer after installing the January Security and Quality update.

• On computers with multiple processor groups, a list used to manage background tasks could stop responding; this issue is addressed.⁵
  Addresses an issue with thread pool recycled lists becoming unresponsive on multi-CPU-group computers.
• A value-reading operation in some 32-bit apps could be much slower on some computers; this issue is addressed.⁶
  Addresses an issue where Interlocked.Read from 32-bit apps is much slower on some computers.

For: Developers using the native C# compiler

• A problem compiling code that calls certain external components is addressed.⁷
  Addresses a problem using the native C# compiler (csc.exe) to compile code making calls to COM interop assemblies.