Microsoft December 2025 Security Updates Disrupt MSMQ on IIS

Microsoft's December 2025 security updates, specifically KB5071546, have caused significant disruptions to Message Queuing (MSMQ) functionality for IIS sites. The patch, installed on December 9, alters MSMQ’s security model, leading to failures in queue operations, particularly in high-load clustered environments. This issue was confirmed on December 12, affecting enterprise administrators relying on MSMQ.