KB5124008 Is Causing Black Screens in Citrix VDI —…

The short version

September servicing (KB5120998 and KB5124008) is causing explorer.exe to fail to start in Citrix VDI environments, leaving users with a black screen after logon. Community workarounds and what to do now.

⚠ Action required for VDI teams: If you have not yet promoted a golden image containing KB5120998 or KB5124008 to your Citrix VDI estate, hold that promotion now. Validate Explorer startup across existing profiles, new profiles, disconnect and reconnect cycles, and fresh logons before proceeding. This is community-reported — no official Microsoft fix exists yet as of 11 September 2026.

What is happening

Administrators running Citrix Virtual Desktop Agent (VDA) environments are reporting a serious regression following the September 2026 Windows servicing cycle. After installing KB5120998 (the August 2026 preview update, released 27 August) or KB5124008 (the September 2026 Patch Tuesday update, released 8 September), users logging into Citrix sessions are presented with a completely black screen. No desktop, no taskbar, no icons — just a blank screen after the logon completes.

The root cause, as identified by the community, is that explorer.exe is not starting automatically after logon in affected environments. The Windows shell process that provides the desktop, taskbar, and Start menu simply does not launch. If a user opens Task Manager manually (pressing Ctrl+Alt+Delete and selecting Task Manager), they can start Explorer themselves from the File menu and the desktop appears immediately — which confirms the session itself is healthy. The problem is specifically the automatic startup of the shell.

Reports began surfacing shortly after KB5120998 was released in August 2026 and increased significantly following the KB5124008 Patch Tuesday rollout on 8 September. The r/Citrix community thread has continued to receive reports of administrators actively reproducing the issue as late as 11 September 2026, covering multiple VDA versions and profile technologies.

📋 Note: This is a community-reported issue. Microsoft still has no release-health entry for the explorer.exe startup failure (checked again 24 September 2026). Citrix, however, now documents it in CTX697101, which lists “Black Screens on Login after installing KB5124008 / KB5120998 on Desktop OS VDAs” and notes that environments combining CVAD with Citrix UPM or FSLogix can still exhibit the issue even after applying the out-of-band updates, with the matter still under investigation. The guidance below reflects what affected administrators in the community have tried and shared.

Who is affected

Not every Citrix environment will see this. The issue appears to be specific to virtualised desktop deployments running the September servicing updates. Physical endpoints are not being reported as affected. Citrix is not the only platform involved, though — reporting also names VMware Horizon and Liquidware ProfileUnity ProfileDisks, with the common factor being user profiles stored in containers rather than Citrix specifically. If you run Horizon or ProfileUnity, do not read this post as an all-clear.

Factor	Affected?
Citrix VDA with KB5120998 installed (Windows 11 24H2 or 25H2)	✅ Yes — confirmed in community reports
Citrix VDA with KB5124008 installed (Windows 11 24H2 or 25H2)	✅ Yes — confirmed in community reports
Environments using FSLogix profile containers	✅ Yes — reported across multiple VDA versions
Environments using Citrix Profile Management containers	✅ Yes — also reported
Fresh (new) user profiles in the Citrix session	✅ Yes — affects new profiles too, not just existing ones
Physical Windows 11 devices (non-VDI)	❌ Not reported with this specific symptom
Citrix environments still on pre-August servicing	❌ No — both updates are the common thread

The fact that both FSLogix and Citrix Profile Management are represented in the reports makes this more credible than a single profile-stack-specific issue. The problem appears to be in the interaction between the September servicing and how the Windows shell initialises in a virtualised session context, rather than in any one profile technology.

⚠ Gotcha: The issue has been reported on both Windows 11 24H2 and 25H2. If you are planning to defer KB5124008 only on 25H2 (where a separate machine secure channel issue also exists), be aware that 24H2 VDI images may be affected by this Explorer startup problem as well. Check both builds in your validation environment.

How to tell if your environment is affected

The symptom is immediately visible to users: after a Citrix session logon completes, they see a black or blank screen with no desktop elements. The session itself is live — the logon succeeded — but the Windows shell (explorer.exe) did not start.

To confirm the issue, have a user or administrator press Ctrl+Alt+Delete during the black screen and open Task Manager. In the Details tab, check whether explorer.exe is listed. If it is not there, the shell did not start — this is the issue. To restore the desktop temporarily, go to File › Run new task, type explorer.exe, and press OK. The desktop should appear immediately.

⚠ Symptom summary — Citrix session after September servicing

What the user sees: Black or blank screen after logon completes
Session state: Logon succeeded — user is authenticated
Missing process: explorer.exe is absent from Task Manager Details tab
Temporary fix: Task Manager › File › Run new task › explorer.exe restores the desktop
Profile types affected: FSLogix containers, Citrix Profile Management, new profiles
Builds affected: Windows 11 24H2 and 25H2 with KB5120998 or KB5124008

The issue is reproducible across connect, disconnect, and reconnect cycles in affected environments. A fresh logon with a brand-new profile also triggers the black screen, which rules out profile corruption as the cause.

What you can do now

Microsoft has not yet published an official fix or workaround for this specific Citrix VDI symptom. The following are approaches that affected administrators in the community have reported trying. These are not officially endorsed workarounds — they are community-sourced suggestions. Test carefully in a non-production environment before applying anything to your estate.

Option 1 — Hold golden image promotion (safest, recommended):

If you have not yet rolled KB5120998 or KB5124008 into your Citrix VDI golden image, the safest action is to hold that promotion until Microsoft or Citrix publishes official guidance. Continue on your current validated servicing level and monitor the release health dashboards linked in the References section below.

✅ Validation checklist before promoting any golden image with September servicing: If you must promote, validate all four of the following scenarios before going to production: (1) existing user profile — logon produces a visible desktop; (2) new user profile — first logon produces a visible desktop; (3) session disconnect then reconnect — desktop is present on reconnect; (4) full logoff then fresh logon — desktop is present. All four must pass. Failure on any one of them means the image is not ready.

Option 2 — Logon script to start Explorer (community-reported approach):

Administrators in the r/Citrix thread have reported using a user logon script that checks whether explorer.exe is running and starts it if not. This can be deployed via a Group Policy user logon script or a Citrix policy logon action. The logic is: if explorer is not found as a running process, launch it. This is a workaround, not a fix — it does not address why the shell failed to start, only recovers the session after the fact. Test on a single VDA in a dev environment before rolling out.

Option 3 — Re-registering XAML and AppX shell components (community-reported, higher risk):

Some administrators have reported attempting to re-register AppX packages on the VDA to restore the shell startup behaviour. This is a more involved operation that touches all installed AppX packages on the system. It has been reported as helping in some environments and having no effect in others. Citrix and Microsoft have not endorsed this approach for this specific issue. If you are considering it, do so only on an isolated test VDA, validate thoroughly, and have a rollback plan. Do not apply it to your production image without confirmed results in your own environment first.

Option 4 — Open a support case:

If you are actively impacted, the most reliable path to a proper fix is to open a Microsoft support case referencing KB5124008, Windows 11 24H2 or 25H2, Citrix VDA, and the explorer.exe black screen symptom. The same applies to Citrix — a Citrix support case with a clear reproduction environment gives both vendors the data they need to investigate and confirm the issue officially. Community workarounds are a holding measure; a vendor-acknowledged fix is the end goal.

Microsoft’s response

As of 11 September 2026, Microsoft has not published a specific release-health entry or support article addressing the explorer.exe startup failure in Citrix VDI environments following September servicing. The Windows 11 release health dashboards are the authoritative places to watch for any acknowledgement or fix:

Citrix administrators are also encouraged to monitor the Citrix Support portal for any VDA-specific guidance related to the September 2026 Windows servicing cycle. Citrix may publish a VDA patch or workaround independently of Microsoft.

The r/Citrix community thread linked in the References section is the most active aggregation point for reproduction reports and field-tested approaches. Contributing your environment details (VDA version, Windows 11 build, profile technology, reproduction steps) to that thread helps build the evidence base for an official vendor response.

References

Updated 24 September 2026: Citrix has since published CTX697101 covering this. Two later Windows updates have shipped — KB5129195 (14 September, out-of-band) and KB5124010 (22 September, preview) — and neither resolves this issue; CTX697101 confirms it survives the out-of-band update. Microsoft has still not published a release-health entry for it.

KB5124008 Is Causing Black Screens in Citrix VDI — Explorer.exe Not Starting After Logon