Microsoft has confirmed that its December 2025 Windows security update (KB5071546, OS Build 19045.6691) is causing Message Queuing (MSMQ) failures, leading to widespread IIS site crashes in enterprise environments.
What’s Happening
- First reported: December 12, updated December 16.
- Symptoms:
- MSMQ queues go inactive, blocking applications from writing messages.
- IIS sites throw “Insufficient resources to perform operation” errors despite sufficient disk/memory.
- Logs show misleading errors like “insufficient disk space or memory.”
- Root cause:
- Patch hardened NTFS permissions on
C:\Windows\System32\MSMQ\storage. - MSMQ users now require explicit write access (previously admin‑only).
- This breaks API calls when sending messages.
- Patch hardened NTFS permissions on
Impact
- Not affected: Consumer setups (Windows Home/Pro).
- Affected: Enterprise environments, especially clustered setups.
- Windows Server 2019, 2016, 2012 R2, 2012.
- Windows 10 versions 22H2, 21H2, 1809, 1607.
- Result: Critical messaging workflows disrupted, cascading into IIS outages.
Microsoft’s Response
- Acknowledged issue on support portal: “We are investigating and will provide updates.”
- No public patch yet.
- Workaround: IT admins must contact Microsoft Support for Business to deploy targeted fixes restoring folder access without weakening security.
Risks & Considerations
- MSMQ is a legacy but vital component for queued messaging in distributed apps (finance, industrial control, etc.).
- IIS failures can idle web services during peak loads.
- Rollback of KB5071546 is possible for non‑clustered systems, but risky for clustered environments (potential data loss).
- Highlights the double‑edged nature of Patch Tuesday: security hardening can inadvertently break critical enterprise workflows.
Recommendations for IT Admins
- Scan environments: Use PowerShell
Get-HotFixor WSUS reports to detect KB5071546. - Contact Microsoft Support: Request targeted workaround deployment.
- Stage testing: Validate updates in controlled environments before production rollout.
- Monitor IIS/MSMQ logs: Watch for inactive queues or misleading resource errors.
- Plan rollback cautiously: Only for non‑clustered systems if outages are severe.
This incident underscores the importance of staged patch testing in enterprise setups. With ransomware and supply‑chain threats looming, balancing security updates against operational stability is critical.
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