December 2025 Patch Tuesday security updates for Windows have unexpectedly disrupted Microsoft Message Queuing (MSMQ) in a number of corporate environments, leading to message queue failures and instability of IIS-based web applications. For organizations that rely on MSMQ for business‑critical workflows, the impact has ranged from degraded performance to full service outages.
Windows December 2025 security updates and affected platforms
According to Microsoft’s current information, the issue affects systems running Windows 10 22H2, Windows Server 2019 and Windows Server 2016 after installing the December 2025 security updates KB5071546, KB5071544 and KB5071543.
MSMQ is an optional Windows component but is widely used in enterprise architectures as a reliable transport layer for asynchronous communication between applications and services. It often underpins internal payment pipelines, task queues, microservice integration and legacy line‑of‑business systems. As a result, even a local MSMQ malfunction can cascade through multiple dependent services.
Typical MSMQ and IIS symptoms after installing KB5071546/44/43
Administrators report a consistent set of symptoms following deployment of the December security updates on servers with MSMQ enabled:
– MSMQ queues remain inactive, appear unavailable or stop processing messages;
– IIS websites and APIs fail with “insufficient resources” or similar errors;
– applications are unable to write messages to queues via the MSMQ API;
– Windows Event Logs and administrative consoles display alerts about low memory or disk space, even when resource utilization is normal.
From an application perspective, these errors resemble classic capacity problems. In reality, many of the failures are triggered by access and permission issues introduced by the recent security hardening.
Root cause: tightened MSMQ security and NTFS permissions
Microsoft links the incident to changes in the MSMQ security model, specifically around NTFS permissions on the critical system directory C:\Windows\System32\MSMQ\storage, which stores data required for queue operations.
After the December 2025 updates, MSMQ service accounts now require write access to this directory. Historically, the folder was predominantly writable only by administrators. Where this new requirement is not met, attempts to write messages through MSMQ can fail and bubble up as generic “resource” errors at the application or IIS layer.
The issue is particularly visible in clustered MSMQ environments under high load. Large volumes of write attempts amplify the problem, causing node instability and, in some cases, affecting multiple cluster nodes simultaneously.
Business and cybersecurity impact of MSMQ outages
For many organizations, MSMQ is a core component of internal transaction processing, request handling and system‑to‑system integration. Disruption of message queues can delay payment processing, prevent customer requests from being accepted, break internal automation and lead to missed SLAs and downtime of mission‑critical services.
This situation also creates a common security dilemma: keep the December security updates and tolerate MSMQ disruption, or roll back the patches to restore functionality, thereby re‑exposing known vulnerabilities. Rolling back may provide short‑term operational relief but increases the attack surface, especially for Internet‑facing Windows servers.
Why rolling back Windows security patches is a high‑risk move
Industry reports such as Verizon’s Data Breach Investigations Report consistently show that exploitation of known, unpatched vulnerabilities remains a key attack vector in many incidents. Large outbreaks like WannaCry and NotPetya spread via systems that delayed or skipped important Windows patches. Reintroducing known vulnerabilities, even temporarily, can violate internal security baselines and regulatory requirements.
If a rollback of KB5071546, KB5071544 or KB5071543 is considered unavoidable for a subset of systems, it should be combined with strong compensating controls: strict network segmentation, limiting exposed services, enhanced logging and monitoring, and, where possible, additional intrusion prevention controls.
Mitigation strategies for Windows and MSMQ administrators
Microsoft has acknowledged the MSMQ issue and is investigating, but there is not yet a published timeline for a permanent fix. In the meantime, organizations can take several practical steps to manage both availability and security:
1. Identify and assess affected systems. Quickly inventory all servers where MSMQ is enabled and the December 2025 updates (KB5071546/44/43) are installed. Prioritize systems based on business criticality and dependency on MSMQ‑based workflows.
2. Confirm the MSMQ permission issue. Review Event Viewer logs (System, Application, MSMQ and IIS) to verify that the failures correlate with MSMQ and directory access problems rather than unrelated resource constraints. Pay particular attention to errors referencing the C:\Windows\System32\MSMQ\storage path or access denied conditions.
3. Adjust NTFS permissions with least privilege. Where confirmed, consider granting the specific MSMQ service identity the necessary write permissions to the MSMQ storage directory instead of broadly relaxing access. This change must be tested first in an isolated or staging environment to avoid introducing new security weaknesses or breaking cluster behavior.
4. Avoid mass rollback of Windows December 2025 security updates. Treat patch removal as a last resort, scoped only to systems where there is no viable workaround and after a structured risk assessment. If rollback is implemented, tighten network exposure, increase security monitoring and track which servers deviate from the standard patch level.
5. Strengthen patch management and testing processes. Use pilot groups and test environments for new Windows cumulative updates, especially when infrastructure relies heavily on components such as MSMQ, IIS and clustering. Formalizing pre‑deployment testing, rollback playbooks and cross‑team communication helps reduce the chance that a future Patch Tuesday will unexpectedly interrupt critical services.
Incidents like the MSMQ failures after the Windows December 2025 security updates highlight how tightly intertwined vulnerability management, change control and business continuity have become. Organizations that maintain an accurate inventory, rigorously test patches, document temporary workarounds and closely monitor Microsoft’s Known Issues guidance are better positioned to protect both security and uptime—and to react quickly when a necessary security update disrupts key services.
