Uncovering the NTLM Zero-Day Threat
New Windows0-day 3.29.25 Protect Your Systems Now!
Discover the latest NTLM vulnerability that allows attackers to steal credentials just by viewing a file. Learn how to safeguard your systems today.
🚨 What Happened?
In March 2025, security researchers dropped a bombshell: a zero-day vulnerability in the NTLM authentication protocol lets attackers capture your credentials when you simply view a malicious .scf file in Windows Explorer.
That’s right — no double-clicking, no running, no opening. If that file hits a Downloads folder or shared drive? Game on.
This affects all major versions of Windows, from Windows 7 to Windows 11 v24H2 and Server 2025.
🎓 Bonus: Free 0patch for Higher Ed & Nonprofits
While Microsoft hasn’t released an official patch yet, the security group 0patch has published a free micropatch for this NTLM vulnerability — and it’s available at no cost to higher education institutions and nonprofits. 0patch delivers small, targeted patches without requiring reboots, making it an excellent stopgap for securing legacy systems or environments with limited IT resources. You can register at 0patch.com and start protecting affected systems right away.
Understanding the NTLM Zero-Day Vulnerability
A Critical Threat to Windows Security
Key Aspects of the NTLM Vulnerability
How the NTLM Zero-Day Works
Credential Capture
Attackers can steal user credentials by exploiting a flaw in the NTLM protocol, simply by viewing a malicious file.
Affected Windows Versions
The vulnerability impacts all major Windows versions, including Windows 7 through Windows 11 v24H2 and Server 2025.
Passive Attack Vector
No need to open or execute files; viewing them in Windows Explorer is enough for credential theft.
NTLM Weakness
NTLM remains a weak spot in many systems, often used for compatibility, leaving networks vulnerable.
Potential Attacks
Once credentials are captured, attackers can impersonate users, relay NTLM credentials, and escalate privileges.
Immediate Mitigations
Organizations should audit NTLM usage, enforce SMB signing, and educate users to mitigate risks.
Long-Term Solutions
Implementing strong password policies and monitoring for suspicious activities can help protect against future threats.
Microsoft's Response
While a patch is in development, organizations must take proactive steps to secure their systems now.
Understanding NTLM Credential Theft
Step 1
When a user views a malicious .scf file in Windows Explorer, the NTLM authentication protocol is triggered.
Step 2
The file sends a request to the user’s system, capturing the NTLM hash without any file opening.
Step 3
Attackers can then use this hash to impersonate users or relay attacks across systems.
Immediate Protection Steps
Implement these measures to safeguard your organization against NTLM vulnerabilities.
1
Audit and Restrict NTLM
Enable logging to track NTLM usage and restrict it using Group Policy.
2
Enforce SMB Signing
Configure SMB signing to prevent credential relaying.
3
Enable Extended Protection
Set up EPA to stop the reuse of relayed credentials.
NTLM Usage Statistics
Over 60% of hybrid environments still rely on NTLM for authentication.
- Hybrid Environments Using NTLM 90%
- Risk of Credential Theft 80%
- Organizations Vulnerable to NTLM Attacks 70%
