How to remediate – Active Directory – Enumerate Users and Groups

1. Introduction

Active Directory – Enumerate Users and Groups retrieves a list of users and their group memberships via ADSI. This allows an attacker with local access to gather information about the Active Directory environment, potentially leading to privilege escalation or further attacks. Systems affected are typically those running Active Directory Domain Services (AD DS). A successful exploit could compromise confidentiality by revealing user account details and group structures.

2. Technical Explanation

The vulnerability occurs because ADSI allows enumeration of users and groups without sufficient access controls. An attacker with local system privileges can query the Active Directory for this information. There is no specific CVE associated with this general enumeration capability, but it represents a core risk in Active Directory security. For example, an attacker could use PowerShell to list all user accounts and their group memberships. Affected platforms are Windows systems running AD DS.

• Root cause: Insufficient access controls on the Active Directory Information Services (ADSI) interface allowing unauthorized enumeration of users and groups.
• Exploit mechanism: An attacker uses a scripting language like PowerShell to query ADSI for user and group information. Example payload: Get-ADUser -Filter * | Select-Object Name, SamAccountName, MemberOf
• Scope: Windows systems running Active Directory Domain Services (AD DS).

3. Detection and Assessment

Confirming vulnerability involves checking if user enumeration is possible with a standard account. A quick check can be done using PowerShell. More thorough assessment requires reviewing ADSI access permissions.

• Quick checks: Run Get-ADUser -Filter * | Select-Object Name, SamAccountName in PowerShell as a non-administrator user. If this returns results, the system is vulnerable.
• Scanning: Nessus plugin ID 10386 can identify Active Directory enumeration vulnerabilities. This is an example only.
• Logs and evidence: Security event logs may show queries to ADSI. Look for Event ID 4768 (A Kerberos authentication ticket was requested).

Get-ADUser -Filter * | Select-Object Name, SamAccountName

4. Solution / Remediation Steps

Remediating this vulnerability requires restricting access to ADSI and implementing the principle of least privilege. These steps aim to limit the information accessible by standard users.

4.1 Preparation

• Dependencies: Ensure you have appropriate administrative privileges to modify Active Directory permissions. Roll back plan: Restore from the pre-change snapshot/backup.
• Change window needs: Implement during a scheduled maintenance window with approval from IT security and system administrators.

4.2 Implementation

1. Step 1: Use Active Directory Users and Computers to modify permissions on the default “Users” container. Deny read access for standard users to the properties that expose user information (e.g., memberOf).
2. Step 2: Review Group Policy Objects (GPOs) to ensure they are not inadvertently granting excessive permissions to ADSI.
3. Step 3: Implement Role-Based Access Control (RBAC) to limit access based on job function, reducing the potential attack surface.

4.3 Config or Code Example

Before

Default "Users" container permissions allowing read access for all authenticated users.

After

Default "Users" container permissions denying read access for standard users to sensitive attributes like memberOf.

4.4 Security Practices Relevant to This Vulnerability

List only practices that directly address this vulnerability type. Use neutral wording and examples instead of fixed advice. For example: least privilege, input validation, safe defaults, secure headers, patch cadence. If a practice does not apply, do not include it.

• Practice 1: Least privilege to reduce the impact if an account is compromised. Grant only necessary permissions for users and groups.
• Practice 2: Input validation to prevent malicious queries or data from being processed by ADSI.

4.5 Automation (Optional)

# PowerShell example to deny read access to memberOf attribute for standard users
# Requires Active Directory module
# Use with caution - test thoroughly before deploying in production
# Get-ADContainer "Users" | Set-ACL -AccessControlType Deny -SecurityDescriptorSddl "D:(A;;GA;;;AU)(OI)(CI)(F)"

5. Verification / Validation

• Post-fix check: Run Get-ADUser -Filter * | Select-Object Name, SamAccountName in PowerShell as a non-administrator user. Expected output: No results or an access denied error.
• Re-test: Re-run the initial detection method (PowerShell query) to confirm that enumeration is no longer possible.
• Smoke test: Verify users can still log in and perform basic tasks, such as accessing email or shared files.
• Monitoring: Monitor security event logs for failed ADSI queries, which may indicate an attempted exploit. Example query: Filter Event ID 4768 for failures related to user enumeration.

Get-ADUser -Filter * | Select-Object Name, SamAccountName

6. Preventive Measures and Monitoring

Suggest only measures that are relevant to the vulnerability type. Use “for example” to keep advice conditional, not prescriptive.

• Baselines: Update security baselines or policies to enforce least privilege access controls for Active Directory objects. For example, implement a CIS control related to AD permissions.
• Pipelines: Add checks in CI/CD pipelines to validate Active Directory configurations and prevent excessive permissions from being granted.
• Asset and patch process: Implement a regular review cycle for Active Directory configurations to identify and remediate potential vulnerabilities.

7. Risks, Side Effects, and Roll Back

• Risk or side effect 2: Incorrect permissions configuration could lock out users. Mitigation: Document all changes and have a roll back plan in place.
• Roll back: Restore from the pre-change snapshot/backup. Revert any modified Active Directory permissions to their original settings.

8. References and Resources

• Vendor advisory or bulletin: Microsoft Active Directory Least Privilege
• NVD or CVE entry: N/A – This is a general configuration issue, not a specific CVE.
• Product or platform documentation relevant to the fix: Active Directory Permissions