How to remediate – Active Directory – Enumerate Group Memberships

1. Introduction

The Active Directory – Enumerate Group Memberships vulnerability allows retrieval of a list of Groups via ADSI. This can expose sensitive information about user and group memberships within an organisation, potentially aiding in further attacks like privilege escalation or targeted phishing. Systems running Active Directory are typically affected. Confidentiality may be impacted due to exposure of membership lists.

2. Technical Explanation

This vulnerability occurs because ADSI allows querying Active Directory for group information without sufficient restrictions. An attacker with local access can enumerate groups and their members, potentially revealing internal organisational structure and user details. There is no known CVE associated with this specific enumeration issue, but it relates to insecure default configurations within Active Directory. For example, an attacker could use PowerShell to query ADSI and list all group memberships. Affected platforms are Windows systems running Active Directory Domain Services.

• Root cause: Insufficient access controls on the ADSI interface for querying group information.
• Exploit mechanism: An attacker uses a script or tool to connect to ADSI and query Active Directory for groups and their members.
• Scope: Windows systems running Active Directory Domain Services.

3. Detection and Assessment

You can confirm vulnerability by checking if group enumeration is possible via PowerShell. A thorough method involves auditing ADSI access logs.

• Quick checks: Run the following PowerShell command to list groups: Get-ADGroup -Filter *. If this returns a list of groups, the system is likely vulnerable.
• Scanning: Nessus plugin ID 10389 can identify Active Directory enumeration vulnerabilities as an example.
• Logs and evidence: Check Windows Event Logs for events related to ADSI access (Event IDs may vary depending on configuration).

Get-ADGroup -Filter *

4. Solution / Remediation Steps

The following steps outline how to mitigate the Active Directory group enumeration vulnerability. These steps should be performed in a controlled environment.

4.1 Preparation

• Ensure you have administrative credentials to modify Active Directory permissions. Roll back plan: Restore the Active Directory backup if issues occur.
• A change window may be needed, and approval from security teams is recommended.

4.2 Implementation

1. Step 1: Implement least privilege access controls on ADSI objects. Restrict permissions to only authorized users and groups.
2. Step 2: Review group memberships regularly to ensure they align with the principle of least privilege.
3. Step 3: Enable auditing for ADSI access to monitor enumeration attempts.

4.3 Config or Code Example

Before

# Default permissions allowing broad access to ADSI objects

After

# Modified permissions restricting access to authorized users and groups only. Use 'Access Control Editor' in Active Directory Users and Computers to configure. 

4.4 Security Practices Relevant to This Vulnerability

Several security practices can help prevent this vulnerability type.

• Practice 1: Least privilege access controls reduce the impact if an attacker gains unauthorized access.
• Practice 2: Regular review of group memberships ensures they align with business needs and least privilege principles.

4.5 Automation (Optional)

# Example PowerShell script to audit ADSI access logs:
# Get-WinEvent -LogName Security | Where-Object {$_.ID -eq 4662} | Format-Table TimeCreated, ID, Message # This is an example only. Adjust the Event ID as needed.

5. Verification / Validation

Confirm the fix by attempting to enumerate groups with a non-administrative account. Verify that access is denied.

• Post-fix check: Run Get-ADGroup -Filter * with a standard user account. Expected output: Access Denied error message.
• Re-test: Re-run the initial PowerShell command (Get-ADGroup -Filter *) as an unprivileged user to confirm access is restricted.
• Smoke test: Verify that authorized users can still perform their normal Active Directory tasks, such as password resets and group membership lookups.
• Monitoring: Monitor Windows Event Logs for failed ADSI access attempts (Event ID may vary).

Get-ADGroup -Filter * # Expected output: Access Denied error message when run by a standard user.

6. Preventive Measures and Monitoring

Update security baselines to include least privilege access controls for ADSI objects. Implement regular patch cycles.

• Baselines: Update your Active Directory security baseline or policy to enforce least privilege access controls on ADSI objects (for example, using Group Policy).
• Pipelines: Include checks in CI/CD pipelines to validate Active Directory permissions and configurations during deployment.
• Asset and patch process: Implement a regular patch cycle for Windows systems running Active Directory Domain Services.

7. Risks, Side Effects, and Roll Back

Incorrectly configuring access controls can disrupt legitimate user access. Restore the Active Directory backup if issues occur.

• Risk or side effect 2: Auditing can generate large log volumes. Mitigation: Configure appropriate filtering and retention policies for audit logs.
• Roll back: Restore the Active Directory database from backup if issues occur.

8. References and Resources

• Vendor advisory or bulletin: Microsoft ADSI Security
• NVD or CVE entry: No specific CVE is associated with this enumeration issue, but related vulnerabilities can be found on the NVD website (https://nvd.nist.gov/).
• Product or platform documentation relevant to the fix: Active Directory Permissions Documentation.