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.
- KB5124008 released September 8, 2026 for Windows 11 24H2/25H2 builds 26100.9445/26200.9445
- Failures show nltest error 1786 and Event 4625 with status 0xC000006D over NTLM
- Suspected cause: Machine Identity Isolation enforcement moving machine secrets into Credential Guard
- Workarounds: disable isolation, reset machine password, run Test-ComputerSecureChannel -Repair, or rejoin the domain
- Out-of-band KB5129195 fixes other issues but not the domain trust failures
From the original article
2 min read at cybersecuritynews.com
Microsoft is investigating reports that the Windows 11 KB5124008 security update is breaking Active Directory domain trust on some enterprise computers, leaving users unable to sign in with valid credentials. The problem appears linked to Machine Identity Isolation, although Microsoft has not confirmed the root cause or published an official workaround. Released on September 8, […]
By Guru Baran · cybersecuritynews.com
A short excerpt; the article and its images belong to the publisher. Summary, key facts and assessment above are AI-written from the article and can be wrong.