kb5128941

KB5128941 is a Microsoft Setup Dynamic Update for Windows 11, version 26H1, released on September 22, 2026. It addresses security vulnerabilities in Windows Setup binaries and other files used during feature updates, replacing the earlier September 8 package, KB5126041. The update applies only to devices already running 26H1 and requires no restart, so most users on that version will not notice it. The tag is most relevant to administrators who maintain 26H1 installation media or offline upgrade images, since a Setup package baked into a deployment share goes stale once Microsoft ships a newer one.