Hayden

In September 2025, Microsoft addressed a critical Windows NTLM privilege escalation vulnerability, CVE-2025-54918, as part of their Patch Tuesday release. This vulnerability poses significant risks, particularly in enterprise environments, and requires immediate attention from system administrators. Microsoft has classified this vulnerability as “Exploitation More Likely,” indicating a high probability of active exploitation.

 

 

1. Understanding CVE-2025-54918: Nature and Risk Assessment

CVE-2025-54918 is a privilege escalation vulnerability discovered in the Windows NT LAN Manager (NTLM) authentication protocol. According to Microsoft’s official advisory, “Improper authentication in Windows NTLM allows an authorized attacker to elevate privileges over a network.”

Core Security Issues

The most concerning aspect of this vulnerability is the ability to achieve remote SYSTEM-level privilege escalation over the network. Security researcher Kev Breen warned that “if an attacker is able to send specially crafted packets over the network to the target device, they would have the ability to gain SYSTEM-level privileges on the target machine.”

CVSS Score: 8.8 (Critical) Attack Complexity: Low User Interaction: None Required Privileges Required: Low

Detailed vulnerability information is available through the Microsoft Security Response Center (MSRC) and Tenable CVE Database.

Attack Scenario Example

Consider an enterprise network where an attacker has gained initial access with standard user credentials. Using CVE-2025-54918, the attack progression would be:

  1. Network reconnaissance to identify NTLM-enabled systems
  2. Transmission of specially crafted authentication request packets
  3. Exploitation of NTLM protocol authentication binding flaws
  4. Immediate escalation from standard user to SYSTEM privileges

This is equivalent to a visitor with basic building access suddenly obtaining master keys to all restricted areas.

 

 

2. Affected Systems and Product Scope

This vulnerability impacts virtually all Windows systems utilizing NTLM authentication, with heightened risk in environments where NTLM remains enabled for legacy service compatibility.

Affected Windows Versions

Operating System Impact Level Notes
Windows 11 (All versions) High Including latest releases
Windows 10 (All versions) High Most widely deployed version
Windows Server 2025 Critical Latest server environment
Windows Server 2022 Critical Core enterprise infrastructure
Windows Server 2019 Critical Widely deployed
Windows Server 2016 Critical Legacy environment risks
Windows Server 2012/2012 R2 Critical Older systems at high risk
Windows Server 2008/2008 R2 Critical Extended support ending

High-Risk Environments

  • Active Directory Domain Environments: Extensive NTLM authentication usage
  • Mixed OS Environments: Networks with Windows and non-Windows systems
  • Legacy Applications: Older software dependent on NTLM authentication
  • File Servers: SMB shares utilizing NTLM authentication
  • Web Servers: IIS implementations using Windows authentication

 

 

3. Technical Analysis and Attack Mechanisms

The NTLM protocol operates through a client-server “challenge-response” mechanism. This vulnerability stems from improper authentication binding validation during this process.

Standard NTLM Authentication Flow

  1. Type 1 Message: Client initiates authentication request to server
  2. Type 2 Message: Server responds with challenge value
  3. Type 3 Message: Client sends response value
  4. Validation: Server verifies response and completes authentication

Vulnerability Exploitation Mechanism

CVE-2025-54918 exploits a identity binding validation failure between steps 3 and 4:

Attacker → [Malformed Type 3 Message] → Vulnerable Server
        ← [Incorrect Privilege Grant] ←

This causes the system to incorrectly recognize low-privilege authentication as high-privilege access, granting SYSTEM-level permissions.

 

 

4. Step-by-Step Patch Implementation Guide

Critical security updates must be applied immediately across all affected systems. Each Windows version requires specific security updates.

Windows 11 Patch Application

Step 1: Windows Update Verification

  • Navigate to Settings → Update & Security → Windows Update
  • Click “Check for updates”

Step 2: Manual Patch Download (if needed)

Step 3: Patch Installation

# Execute in elevated Command Prompt
dism /online /add-package /packagepath:C:\path\windows11.0-kb5065426-x64.msu

Windows 10 Patch Application

Applicable KB Updates: Version-specific requirements

  • Windows 10 22H2: Verify specific KB requirements
  • Windows 10 21H2: Verify specific KB requirements

Windows Server Series Patches

Windows Server 2025

  • Apply KB5065426
  • PowerShell verification:
Get-HotFix -Id KB5065426

Windows Server 2022/2019/2016

  • Apply version-specific monthly security updates
  • Recommend batch deployment via WSUS or Windows Update

Enterprise Environment Batch Patching

WSUS (Windows Server Update Services) Implementation

  1. Access WSUS console and verify “Security Updates” category
  2. Approve CVE-2025-54918 related updates
  3. Deploy in phases by computer groups

SCCM (System Center Configuration Manager) Implementation

  1. Synchronize Software Update workspace
  2. Create Automatic Deployment Rules (ADR)
  3. Schedule deployment within maintenance windows

 

 

5. Post-Patch Verification and Validation

Patch application verification is mandatory to ensure successful deployment.

System Information Verification

Method 1: System Information

msinfo32
  • Navigate to System Summary → Installed Hotfixes

Method 2: PowerShell Commands

# Verify specific KB installation
Get-HotFix | Where-Object {$_.HotFixID -eq "KB5065426"}

# List recent installations
Get-HotFix | Sort-Object InstalledOn -Descending | Select-Object -First 10

Method 3: Windows Update History

  • Settings → Update & Security → “View update history”

Event Log Verification

Windows Event Viewer provides patch application logging:

  1. Launch Event Viewer (eventvwr.msc)
  2. Navigate to Windows Logs → System
  3. Filter Source: “Microsoft-Windows-WindowsUpdateClient”
  4. Review recent update installation Event IDs 19, 20, 43

 

 

6. Additional Security Hardening and Best Practices

Patching alone is insufficient. Implement comprehensive security measures to enhance overall security posture.

NTLM Usage Minimization

Kerberos Authentication Migration

  • Configure Kerberos as default authentication in domain environments
  • Implement NTLM restrictions via Group Policy:
    • Computer Configuration → Windows Settings → Security Settings → Local Policies → Security Options
    • Configure “Network security: LAN Manager authentication level”

SMB Signing Activation

# Force SMB signing via registry
reg add HKLM\SYSTEM\CurrentControlSet\Services\LanmanServer\Parameters /v RequireSecuritySignature /t REG_DWORD /d 1

For detailed SMB security hardening, reference Microsoft’s official technical documentation regarding CVE-2025-55234 guidelines.

Network Segmentation and Access Controls

  • Network Segmentation: Isolate critical systems in separate VLANs
  • Firewall Rules: Implement strict NTLM traffic access controls
  • Zero Trust Model: Apply “never trust, always verify” principles

Monitoring and Detection Systems

Security Event Monitoring

  • Track NTLM authentication events in Windows Security logs
  • Monitor Event IDs 4624, 4625, 4648 for authentication activities
  • Implement SIEM solutions for real-time analysis

Anomaly Detection

  • Detect unusual privilege escalation attempts
  • Analyze per-account access patterns
  • Monitor network traffic anomalies

 

 

7. Organization-Specific Response Strategies

Small Organizations (Under 50 users)

Priority: Immediate patch deployment

  • Enable Windows Update automatic updates
  • Prioritize critical servers with manual patching
  • Utilize weekend or off-hours for deployment

Recommended Tools: Windows Update for Business

  • Basic Windows Defender utilization
  • Microsoft Update Catalog for manual downloads
  • Priority patching for critical systems

Medium Organizations (50-500 users)

Phased Approach:

  1. Phase 1: Test environment patch validation (1-2 days)
  2. Phase 2: Critical server priority patching (weekend)
  3. Phase 3: Sequential client PC patching (1 week)

Recommended Tools:

  • WSUS or Windows Update for Business
  • Microsoft Defender for Business
  • Basic logging and monitoring

Large Enterprises (500+ users)

Systematic Management:

  • Change Management Process: CAB (Change Advisory Board) approval
  • Risk Assessment: Business impact analysis
  • Rollback Planning: Immediate recovery procedures for issues

Recommended Tools:

  • SCCM or Microsoft Intune
  • Microsoft Defender for Endpoint
  • Azure Sentinel or third-party SIEM
  • PowerShell DSC for configuration management

 

 

8. Troubleshooting and Considerations

Potential Patch Application Issues

1. Compatibility Problems Legacy applications may experience NTLM authentication issues.

  • Resolution: Request compatibility updates from application vendors
  • Temporary Solution: Configure NTLM exceptions for specific systems (not recommended)

2. Performance Impact Additional authentication validation may cause minor performance degradation.

  • Resolution: Optimize authentication caching, verify hardware resources

3. PowerShell Direct Connection Issues Microsoft-confirmed known issue where Hotpatch application may cause PowerShell Direct connection problems between virtual machines.

Emergency Response Procedures

If serious issues occur post-patch:

1. Immediate Actions

# Remove specific update (last resort)
wusa /uninstall /kb:5065426 /quiet /norestart

2. Log Collection

# Collect Windows Update logs
Get-WindowsUpdateLog -LogPath C:\WindowsUpdate.log

3. Microsoft Support Contact

 

The Windows NTLM CVE-2025-54918 vulnerability serves as a critical reminder of legacy protocol risks and the importance of rapid patch deployment. Organizations should particularly focus on gradually migrating from older authentication methods like NTLM to more secure alternatives.

 

 

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