CVE-2025-21181
📋 TL;DR
A denial-of-service vulnerability in Microsoft Message Queuing (MSMQ) allows attackers to crash the service by sending specially crafted messages. This affects systems running MSMQ on supported Windows versions. The vulnerability requires network access to the MSMQ service.
💻 Affected Systems
- Microsoft Message Queuing (MSMQ)
📦 What is this software?
Windows 10 1507 by Microsoft
Windows 10 1507 by Microsoft
Windows 10 1607 by Microsoft
Windows 10 1607 by Microsoft
Windows 10 1809 by Microsoft
Windows 10 1809 by Microsoft
Windows 10 21h2 by Microsoft
Windows 10 22h2 by Microsoft
Windows 11 22h2 by Microsoft
Windows 11 23h2 by Microsoft
Windows 11 24h2 by Microsoft
⚠️ Risk & Real-World Impact
Worst Case
Complete unavailability of MSMQ service, disrupting dependent applications and business processes that rely on message queuing functionality.
Likely Case
Temporary service disruption requiring manual restart of MSMQ service, causing application timeouts and degraded performance.
If Mitigated
Minimal impact with proper network segmentation and monitoring allowing quick detection and response.
🎯 Exploit Status
Exploitation requires network access to MSMQ service port (typically TCP 1801). No authentication needed to trigger the DoS condition.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Latest Windows security updates for May 2025 or later
Vendor Advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2025-21181
Restart Required: Yes
Instructions:
1. Apply latest Windows security updates from Microsoft Update or WSUS. 2. Restart affected systems to complete installation. 3. Verify MSMQ service is running normally after restart.
🔧 Temporary Workarounds
Disable MSMQ Service
WindowsStop and disable MSMQ service if not required for business operations
Stop-Service -Name MSMQ
Set-Service -Name MSMQ -StartupType Disabled
Block MSMQ Ports
WindowsBlock network access to MSMQ ports using firewall rules
New-NetFirewallRule -DisplayName "Block MSMQ" -Direction Inbound -LocalPort 1801 -Protocol TCP -Action Block
🧯 If You Can't Patch
- Implement strict network segmentation to limit access to MSMQ services
- Monitor MSMQ service health and implement automated restart scripts for service recovery
🔍 How to Verify
Check if Vulnerable:
Check if MSMQ service is installed and running: Get-WindowsFeature MSMQ or Get-Service MSMQCheck Version:
Get-ItemProperty "HKLM:\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\*" | Where-Object {$_.DisplayName -like "*Message Queuing*"} | Select-Object DisplayName, DisplayVersionVerify Fix Applied:
Verify Windows Update history contains May 2025 security updates and MSMQ service version is updated📡 Detection & Monitoring
Log Indicators:
- MSMQ service crash events in Windows System logs
- Event ID 7031 for MSMQ service termination
- Multiple connection attempts to port 1801
Network Indicators:
- Unusual traffic patterns to MSMQ port 1801
- Multiple malformed packets to MSMQ service
SIEM Query:
source="windows" AND (event_id=7031 AND service_name="MSMQ") OR (destination_port=1801 AND packet_size>threshold)🔗 References
- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2025-21181
- https://www.vicarius.io/vsociety/posts/cve-2025-21181-denial-of-service-vulnerability-in-microsoft-message-queuing-detection-script
- https://www.vicarius.io/vsociety/posts/cve-2025-21181-denial-of-service-vulnerability-in-microsoft-message-queuing-mitigation-script
