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A new Patch Tuesday, a new surprise. This time, Citrix VDA registration is affected.
After installing Windows 11 security update KB5127648 (October 2026), Citrix Virtual Delivery Agents may suddenly fail to register with the Delivery Controller.
The interesting part: the VDA is reachable and RDP works, but Citrix remains stuck at Registering.
🔍 The symptoms
– Citrix Studio: Trying to re-register
– VDA status remains at Registering
– Published desktops cannot be launched
– RDP to the affected machine still works
Citrix officially documents the issue under CTX697231 for Windows 11 24H2/25H2, reported with VDA 2511. Other VDA versions may also be affected.
🔬 The decisive clue is in the event log
On the Delivery Controller:
Event ID 131075
Process: BrokerService.exe
Exception:
System.ServiceModel.Security.SecurityNegotiationException
Error message:
The caller was not authenticated by the service.
Affected operation:
Citrix.Cds.Protocol.Worker.IQueryAgent.Test()
This is where it gets interesting: the problem is not basic Controller connectivity, but authentication during communication between the Broker Service and VDA.
🛠️ The workaround
Citrix has already published a tested mitigation:
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reg add HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System /v TypeOfAdminApprovalMode /t REG_DWORD /d 1 /f |
Then restart the affected VDA.
The registry value switches from the new Windows Administrator Protection to classic Admin Approval Mode.
Citrix confirms that affected VDAs register successfully again afterwards.
⚠️ Important: this is a temporary workaround that rolls back an additional Windows security feature. Apply the change in a controlled manner and reassess it after a permanent fix becomes available.
💡 What can we learn?
A VDA that fails to register after Patch Tuesday does not necessarily have a Citrix issue.
And working RDP does not mean that Citrix Broker authentication is working too.
Before reinstalling VDAs, repairing Delivery Controllers or dismantling the Active Directory configuration:
Check KB5127648, Event ID 131075 and TypeOfAdminApprovalMode.
Citrix and Microsoft continue to investigate the underlying cause together.
📚 Source:
