CVE-2026-20872
📋 TL;DR
This vulnerability allows an attacker to manipulate file paths in Windows NTLM authentication, enabling network spoofing attacks. Attackers could impersonate legitimate users or systems by controlling file names or paths during NTLM exchanges. This affects systems using Windows NTLM authentication, particularly in enterprise environments.
💻 Affected Systems
- Windows NTLM implementation
📦 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 23h2 by Microsoft
Windows 11 24h2 by Microsoft
Windows 11 25h2 by Microsoft
⚠️ Risk & Real-World Impact
Worst Case
Complete network compromise through credential theft, lateral movement across domain, and privilege escalation to domain administrator.
Likely Case
Unauthorized access to network resources, data exfiltration, and limited lateral movement within the same network segment.
If Mitigated
Isolated authentication failures or blocked connection attempts with proper network segmentation and monitoring.
🎯 Exploit Status
Exploitation requires network access to NTLM endpoints and ability to manipulate authentication flows.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check Microsoft Security Update Guide for specific KB numbers
Vendor Advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-20872
Restart Required: Yes
Instructions:
1. Apply latest Windows security updates from Microsoft Update. 2. Restart affected systems. 3. Verify NTLM-related services are updated.
🔧 Temporary Workarounds
Disable NTLM authentication
windowsReplace NTLM with Kerberos authentication where possible
Group Policy: Computer Configuration > Windows Settings > Security Settings > Local Policies > Security Options > Network security: Restrict NTLM
Implement network segmentation
allIsolate systems using NTLM from untrusted networks
🧯 If You Can't Patch
- Implement strict network segmentation to isolate NTLM traffic
- Deploy network monitoring and IDS/IPS rules to detect NTLM manipulation attempts
🔍 How to Verify
Check if Vulnerable:
Check if systems are using NTLM authentication and have not applied the security updateCheck Version:
systeminfo | findstr /B /C:"OS Name" /C:"OS Version"Verify Fix Applied:
Verify Windows Update history contains the relevant security update and NTLM services are running patched versions📡 Detection & Monitoring
Log Indicators:
- Unusual NTLM authentication patterns
- Failed authentication attempts with manipulated paths
- Security event ID 4625 with NTLM
Network Indicators:
- Abnormal NTLM traffic patterns
- Suspicious file path references in authentication packets
SIEM Query:
source="windows-security" event_id=4625 authentication_package="NTLM" | search suspicious_path_patterns