Windows 11 Security Update KB5124008 Breaks Always-On VPN Connections
Microsoft's September 2026 Windows 11 update KB5124008 breaks certificate-based Always On VPN on some enterprise clients, forcing admins to pause rollout.
Microsoft's September 8, 2026 cumulative update KB5124008 for Windows 11 24H2 (build 26100.9445) and 25H2 (build 26200.9445) breaks certificate-based Always On VPN tunnels on some enterprise clients, with connectivity restored after uninstalling the update and rebooting. The issue was first detailed on Microsoft Q&A on September 9 by an administrator using Intune-deployed VPN profiles with RRAS and NPS on Windows Server 2019. The same mandatory Patch Tuesday package fixes two actively exploited zero-days, CVE-2026-81963 in the Windows Update Stack and CVE-2026-85880 in Windows Advanced Local Procedure Call, so many teams are pausing only VPN cohorts rather than blocking the full rollout.
Windows 11 KB5124008 Update Breaks Active Directory Domain Trust and Blocks User Logins
Microsoft's September Windows 11 cumulative update KB5124008 breaks Active Directory domain trust on domain-joined machines, blocking logins despite valid credentials.
Microsoft is investigating community reports that KB5124008, the September 8, 2026 cumulative update for Windows 11 24H2/25H2 (builds 26100.9445/26200.9445), breaks the AD secure channel, causing 'The user name or password is incorrect' errors on interactive logon. Admins reproduced the failure consistently and observed nltest error 1786 (ERROR_NO_TRUST_LSA_SECRET) plus domain controller Event 4625 with status 0xC000006D over NTLM. The problem is suspected in Machine Identity Isolation, a Credential Guard capability that moves machine-account secrets into virtualization-based security, and disabling it via registry value, Group Policy, or Intune baseline restored trust. The September 14 out-of-band update KB5129195 does not address the domain trust issue, and Microsoft's release notes do not list it as a known problem.