OVERSEER NOTE: As of April 14, 2026, Microsoft has entered the final enforcement phase for RPC (Remote Procedure Call) protocol hardening. This isn’t a “soft” warning anymore—systems that do not meet the new authentication level requirements are being summarily rejected with “Access Denied” or “RPC Server Unavailable” errors.
If your legacy printers, scanners, or older application servers suddenly went dark after the April LCU, you are likely a victim of the lockdown.
The Diagnostic: Identifying the Block
Before hacking at the registry, verify the fallout in your Event Logs:
- Open Event Viewer on the server receiving the RPC calls.
- Navigate to:
System Logs. - Look for Event ID 38: This specifically logs when an RPC client attempts to connect with an authentication level below the new “Enforced” threshold.
The “Band-Aid” Remediation
If critical business operations are halted, you can temporarily downgrade the enforcement to “Compatibility Mode” via the registry.
WARNING: This should only be used as a stop-gap while you upgrade your client software or hardware.
Registry Path: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Print
Action: Create a DWORD (32-bit) value named RpcAuthnLevelPrivacyEnabled and set it to 0.
Command Line (Admin):
reg add "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Print" /v RpcAuthnLevelPrivacyEnabled /t REG_DWORD /d 0 /f
Note: A restart of the “Print Spooler” service is required for this to take effect.
The Long-Term Fix
The permanent solution is ensuring all clients utilize Packet Privacy (RPC_C_AUTHN_LEVEL_PKT_PRIVACY).
- For Devs: Update your connection strings to enforce encrypted RPC.
- For Admins: Move legacy print workflows to a modern Print Server Role that supports the updated protocol stack.
VIGILANCE NOTE: Microsoft plans to remove the “Band-Aid” registry bypass entirely by October 2026. You have six months to modernize your legacy infrastructure before the lockdown becomes permanent.