Abusing Client-Side Extensions (CSE): A Backdoor into Your AD Environment

By /

Listen to this Post

Featured Image
Client-Side Extensions (CSEs) in Active Directory (AD) Group Policy Objects (GPOs) can be exploited for persistence, allowing attackers to maintain access even after initial compromise. This technique leverages CSEs to execute malicious payloads whenever a GPO is applied.

Read the full article here: Tenable – Abusing Client-Side Extensions

You Should Know:

1. Identifying Vulnerable CSEs

Use PowerShell to list all CSEs in your AD environment:

Get-ChildItem "HKLM:\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\GPExtensions" | Select-Object PSChildName

2. Modifying CSE for Persistence

Attackers can inject malicious DLLs into CSEs. Check for unauthorized changes with:

Get-ItemProperty "HKLM:\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\GPExtensions\DllName" | Select-Object PSChildName, DllName

3. Detecting Malicious GPO Changes

Audit GPO modifications using `gpresult`:

gpresult /h report.html

Or with PowerShell:

Get-GPOReport -All -ReportType Html -Path "C:\GPOReport.html"

4. Hunting for CSE-Based Backdoors

Use Sysmon to monitor CSE-related process creations:

<EventFilter>
<RuleGroup name="CSE Abuse Detection">
<ProcessCreate onmatch="include">
<CommandLine condition="contains">CSE</CommandLine>
</ProcessCreate>
</RuleGroup>
</EventFilter>

5. Mitigation Steps

  • Restrict GPO modification rights.
  • Enable SACL (Auditing) on CSE registry keys:
    auditpol /set /subcategory:"Registry" /success:enable /failure:enable
  • Monitor Event ID 4657 (Windows Registry Auditing).

What Undercode Say:

CSE abuse is a stealthy persistence mechanism that bypasses traditional detection. Defenders must:
– Regularly audit GPOs and CSE registries.
– Implement least privilege for GPO management.
– Use KQL (Kusto Query Language) for hunting in Azure Sentinel:

SecurityEvent | where EventID == 4657 | where RegistryKeyPath contains "Winlogon\GPExtensions"

– Deploy LOLBAS (Living Off the Land Binaries) monitoring to catch abuse of legitimate tools like `powershell.exe` loading malicious CSE DLLs.

Expected Output:

  • A hardened AD environment with monitored CSE execution.
  • Alerts for unauthorized GPO modifications.
  • Reduced attacker dwell time via proactive CSE auditing.

Prediction:

As AD environments evolve, attackers will increasingly abuse lesser-known features like CSEs for evasion. Expect more fileless persistence techniques leveraging GPOs in 2025.

Expected Output:

  • Increased detection of CSE-based attacks in enterprise logs.
  • More defensive tools integrating CSE-specific monitoring.

IT/Security Reporter URL:

Reported By: 0x534c Abusing – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅

Join Our Cyber World:

💬 Whatsapp | 💬 Telegram

Related Posts: