CVE-2025-21254
📋 TL;DR
This vulnerability in Internet Connection Sharing (ICS) allows attackers to cause a denial of service by exploiting an out-of-bounds read condition. It affects Windows systems with ICS enabled, potentially causing system instability or crashes. The vulnerability requires local network access to exploit.
💻 Affected Systems
- Windows Internet Connection Sharing
📦 What is this software?
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 system crash or blue screen requiring reboot, disrupting all network connectivity and services on the affected system.
Likely Case
Temporary service disruption or system instability affecting ICS functionality and potentially other network services.
If Mitigated
Minimal impact with proper network segmentation and access controls limiting exposure to trusted networks only.
🎯 Exploit Status
Requires network access to the ICS service and knowledge of the vulnerability trigger conditions.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Latest Windows security updates for affected versions
Vendor Advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2025-21254
Restart Required: Yes
Instructions:
1. Apply latest Windows security updates via Windows Update. 2. Alternatively, download and install the specific security update from Microsoft Update Catalog. 3. Restart the system to complete installation.
🔧 Temporary Workarounds
Disable Internet Connection Sharing
windowsTemporarily disable ICS to eliminate the attack surface
netsh wlan set hostednetwork mode=disallow
Disable ICS in Network Connections properties
Network Segmentation
allIsolate systems with ICS enabled from untrusted networks
🧯 If You Can't Patch
- Disable Internet Connection Sharing feature completely
- Implement strict network access controls to limit ICS exposure to trusted hosts only
🔍 How to Verify
Check if Vulnerable:
Check if ICS is enabled via Network Connections properties or 'netsh wlan show hostednetwork' commandCheck Version:
systeminfo | findstr /B /C:"OS Name" /C:"OS Version"Verify Fix Applied:
Verify Windows Update history shows the security update installed and ICS remains functional📡 Detection & Monitoring
Log Indicators:
- System event logs showing ICS service crashes
- Application logs with ICS-related errors
- Unexpected system reboots
Network Indicators:
- Unusual network traffic patterns to ICS ports
- Multiple connection attempts to ICS service
SIEM Query:
EventID=1000 OR EventID=1001 AND SourceName contains 'ics' OR ProcessName contains 'svchost' AND CommandLine contains 'ics'