Microsoft has released security updates in September 2025 Patch Tuesday addressing a serious flaw: CVE-2025-54918. This vulnerability impacts Windows NTLM authentication and could allow attackers to gain SYSTEM-level privileges, making it a high-priority risk for organizations.
What is CVE-2025-54918?
CVE-2025-54918 is an Elevation of Privilege (EoP) vulnerability in Windows NTLM.
Due to improper authentication handling, attackers with network access can abuse NTLM to escalate their privileges. Once exploited, the attacker could take full control of the affected system.
- Vulnerability Type: Elevation of Privilege
- Affected Component: NTLM Authentication
- Severity Score (CVSS v3.1): 8.8 (High)
- Exploitability: Rated “Exploitation More Likely” by Microsoft
Why It Matters
- Successful exploitation grants SYSTEM privileges (the highest level of access in Windows).
- Attackers could install malware, steal sensitive data, disable defenses, or move laterally inside networks.
- This is the third NTLM privilege escalation flaw patched in 2025, showing attackers are actively targeting NTLM.
Who Is Affected?
Any Windows environment still using NTLM authentication is potentially exposed.
This includes:
- Legacy systems and applications dependent on NTLM
- Domain environments where NTLM fallback is enabled
- Servers and endpoints communicating over NTLM
How Attackers Exploit It
- Gain initial access through phishing, stolen credentials, or another foothold
- Use NTLM to abuse improper authentication
- Escalate to SYSTEM privileges
- Deploy malware, exfiltrate data, or spread across the network
How to Protect Against CVE-2025-54918
1. Apply Microsoft’s September 2025 Patch Tuesday Updates
Install patches immediately across servers and endpoints.
2. Audit NTLM Usage
Check where NTLM is still in use in your network. Tools and Windows logs can help track NTLM authentication.
3. Disable or Restrict NTLM
Where possible, migrate to stronger authentication protocols like Kerberos. Disable NTLM where it is not needed.
4. Strengthen Security Controls
- Segment networks to reduce attack surfaces
- Apply least-privilege principles
- Enable advanced logging and monitoring for NTLM activity
5. Prepare for Incident Response
Update detection rules, run security drills, and ensure your SOC team is aware of this vulnerability.
Final Thoughts
CVE-2025-54918 is a high-severity vulnerability that should not be ignored. Because NTLM is still present in many enterprise environments, attackers are likely to target it as a fast track to SYSTEM access.
The best defense is a patch-first strategy, combined with a long-term goal of eliminating NTLM dependencies. Organizations that move quickly will significantly reduce their risk of privilege escalation attacks.
