Microsoft's December 2025 security updates created an unforeseen problem for administrators of Message Queuing (MSMQ) -based systems .
See also: Microsoft: 'In Scope by Default' makes all vulnerabilities eligible for bug bounties
The update, which was installed on December 9 via KB5071546 and affects OS Build 19045.6691, modifies the MSMQ security model, resulting in widespread failures in queue operations.
The issue was confirmed on December 12th and is most pronounced in clustered environments with high load, where queues become inactive and websites hosted on IIS crash, displaying vague "Insufficient resources" errors.
The bug became apparent almost immediately after Patch Tuesday, affecting older but critical applications that depend on MSMQ in the finance, healthcare, and supply chain sectors.
Users report that applications freeze and fail to write messages, despite having sufficient available disk space and RAM. The impact disrupts real-time messaging flows, forcing IT teams to constantly and urgently troubleshoot.
See also: Microsoft Patch Tuesday December 2025 released
Administrators are faced with a cascade of errors: MSMQ queues are “dying,” interrupting the flow of messages.
IIS websites are throwing exceptions like “Insufficient resources to perform operation.” Failed writes result in errors like “Unable to create message file 'C:\Windows\System32\msmq\storage*.mq'.” Log files are misleadingly attributing the problem to “insufficient disk space or memory.”
The cause is found in stricter NTFS permissions on the C:\Windows\System32\MSMQ\storage folder. After the update, non -administrator MSMQ users do not have write access, which conflicts with how the service works and leads to a resource denial pause. Microsoft acknowledges that the issue is related to MSMQ security hardening and is under investigation. There is no immediate solution, however, it is recommended to check the folder permissions or temporarily pause MSMQ in clustered environments until an official fix is available. “ We will provide more information soon ,” the relevant announcement states.
See also: Microsoft Patch Tuesday December 2025 released
For now, it is recommended to defer installation of KB5071546 in environments that heavily depend on MSMQ or test it first in a staging environment. This incident adds to a series of Patch Tuesday mishaps highlighting the risks of automatic updates in critical Windows ecosystems.
