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.
- KB5124008 breaks certificate-based Always On VPN on Windows 11 24H2 and 25H2 enterprise clients.
- Uninstalling the cumulative update and rebooting reliably restores VPN connectivity on affected machines.
- The same update patches two actively exploited zero-days: CVE-2026-81963 and CVE-2026-85880.
- Microsoft's support article says it is not currently aware of any issues with the update.
- Experts recommend pausing rollout on VPN endpoints and collecting RasClient and NPS logs.
- Vendors
- Microsoft
Vulnerabilities mentioned
All| CVE | Vulnerability | CVSS | EPSS | Signals | Published |
|---|---|---|---|---|---|
CVE-2026-81963+1 related CVE | Local Privilege Escalation via Link Following in Windows Update Stack | 7.8 | <1% | KEV | KEV |
From the original article
3 min read at cybersecuritynews.com
Microsoft’s September 2026 security update KB5124008 is knocking some Windows 11 enterprise clients off Always On VPN after the Patch Tuesday package landed on September 8. Administrators who can reproduce the failure say certificate-based tunnels that worked immediately before the patch stop connecting afterward, then recover as soon as the cumulative update is removed and […]
By Guru Baran · cybersecuritynews.com
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