CVE-2020-0904
📋 TL;DR
A denial of service vulnerability in Microsoft Hyper-V allows an attacker with privileged access on a guest virtual machine to crash the host server by sending malicious data. This affects organizations running Hyper-V virtualization with untrusted or compromised guest VMs. The vulnerability requires an attacker to already have elevated privileges within a guest VM.
💻 Affected Systems
- Microsoft Hyper-V
📦 What is this software?
Windows 10 by Microsoft
Windows 10 by Microsoft
Windows 10 by Microsoft
Windows 10 by Microsoft
Windows 10 by Microsoft
Windows 10 by Microsoft
Windows 10 by Microsoft
Windows 10 by Microsoft
⚠️ Risk & Real-World Impact
Worst Case
Complete host server crash leading to denial of service for all virtual machines running on that host, potentially causing business disruption and data loss.
Likely Case
Host server instability or crash affecting multiple VMs, requiring manual intervention and downtime to restore services.
If Mitigated
Minimal impact if guest VMs are properly secured and monitored, with rapid detection and isolation of compromised VMs.
🎯 Exploit Status
Requires attacker to already have administrative access to a guest VM and knowledge of the vulnerability to craft malicious requests.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: March 2020 security updates for affected Windows versions
Vendor Advisory: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2020-0904
Restart Required: Yes
Instructions:
1. Apply March 2020 security updates from Windows Update. 2. For Windows Server, use Windows Server Update Services (WSUS). 3. Restart affected Hyper-V hosts after patching.
🔧 Temporary Workarounds
Isolate guest VMs
allSegment guest VMs into separate virtual networks and limit communication between VMs to reduce attack surface.
Restrict guest VM privileges
allImplement least privilege access controls on guest VMs to prevent attackers from gaining administrative access needed for exploitation.
🧯 If You Can't Patch
- Implement strict access controls and monitoring on guest VMs to detect and prevent privilege escalation
- Isolate critical Hyper-V hosts from general network access and implement network segmentation
🔍 How to Verify
Check if Vulnerable:
Check if Hyper-V role is enabled and verify Windows version is before March 2020 updates. Use: Get-WindowsFeature -Name Hyper-VCheck Version:
wmic os get Caption,Version,BuildNumberVerify Fix Applied:
Verify Windows Update history shows March 2020 security updates installed and Hyper-V service is running normally.📡 Detection & Monitoring
Log Indicators:
- Hyper-V host crashes or unexpected restarts
- Event ID 41 in Windows System logs (unexpected shutdown)
- Increased Hyper-V error events
Network Indicators:
- Unusual traffic patterns from guest VMs to Hyper-V host management interfaces
SIEM Query:
EventID=41 AND Source="Microsoft-Windows-Kernel-Power" AND ComputerName contains "HYPERV"