kb5120999

KB5120999 is a Safe OS Dynamic Update for Windows 11 version 26H1, released by Microsoft on August 11, 2026. It updates the Windows Recovery Environment (WinRE) to version 10.0.28000.2703, replacing the previous update KB5101717. This update installs without requiring a restart and is delivered through Windows Update, the Microsoft Update Catalog, and Windows Server Update Services. It is a recovery-partition update, not a standard cumulative update for the running OS. IT teams managing Windows 11 26H1 deployment media, recovery images, and managed fleets should apply it to ensure WinRE is patched and verifiable.