MSMQ functionality

Microsoft has acknowledged a significant issue with the December 2025 security updates that disrupts Message Queuing (MSMQ) functionality, affecting enterprise applications and Internet Information Services (IIS) websites. The problem is prevalent among systems running Windows 10 22H2, Windows Server 2019, and Windows Server 2016 with security updates KB5071546, KB5071544, and KB5071543. Users are experiencing inactive MSMQ queues, IIS sites failing with "insufficient resources" errors, applications unable to write to queues, and misleading error messages about "insufficient disk space or memory." The root cause is changes to the MSMQ security model that altered permissions on the C:WindowsSystem32MSMQstorage folder, requiring MSMQ users to have write access to a directory typically reserved for administrators. Devices with users logged in as administrators are not affected. Microsoft is investigating the issue but has not provided a timeline for resolution. Rolling back the updates is a potential solution for administrators, though it carries security risks. This follows a warning from Microsoft in April 2023 about a critical vulnerability in the MSMQ service.