How to remediate – Windows Enumerate Accounts

1. Introduction

Windows Enumerate Accounts allows an attacker to list user accounts on a Windows system. This can help them plan further attacks, such as privilege escalation or data theft. Systems running Windows are usually affected. A successful exploit could compromise confidentiality by revealing account names and potentially other information.

2. Technical Explanation

The vulnerability occurs because of default permissions allowing local users to query account information. An attacker with local access can use standard tools to enumerate accounts. There is no specific CVE associated with this general enumeration capability, but it’s a common reconnaissance step in many attacks. For example, an attacker could use the `net user` command to list all accounts on a compromised machine. Affected systems include Windows versions where default account enumeration permissions have not been modified.

• Root cause: Insufficient restrictions on access to account information.
• Exploit mechanism: An attacker uses built-in tools or APIs to query the system for user accounts. Example payload: `net user`.
• Scope: All Windows versions are potentially affected, depending on configuration.

3. Detection and Assessment

You can confirm vulnerability by checking if account enumeration is possible with a standard local user account. A quick check involves running the `net user` command. More thorough assessment uses tools like PowerShell to query Active Directory or SAM database directly.

• Quick checks: Run net user from a command prompt as a non-administrator user. If accounts are listed, the system is vulnerable.
• Scanning: Nessus plugin ID 10386 can detect account enumeration issues. This is an example only.
• Logs and evidence: Security event logs may show queries to the SAM database or Active Directory related to account information. Look for Event IDs 4768 (A Kerberos authentication ticket was requested) or similar events indicating account lookups.

net user

4. Solution / Remediation Steps

The following steps reduce the risk of account enumeration. These are best applied during a scheduled maintenance window.

4.1 Preparation

• Ensure you have local administrator credentials for roll back. A roll back plan involves restoring the system snapshot.
• Changes should be approved by the security team.

4.2 Implementation

1. Step 1: Restrict access to the SAM database using Group Policy or Local Security Policy.
2. Step 2: Configure auditing to log account enumeration attempts.
3. Step 3: Review and update user rights assignments, ensuring least privilege is applied.

4.3 Config or Code Example

Before

Default permissions allow local users to query account information.

After

Restrict 'SeBackupPrivilege' and 'SeRestorePrivilege' for local user accounts on the SAM database. Configure auditing of access attempts.

4.4 Security Practices Relevant to This Vulnerability

Several security practices help prevent this issue.

• Practice 1: Least privilege reduces the impact if an account is compromised. Limit user rights and permissions to only what’s needed.
• Practice 2: Input validation can block attempts to query sensitive information.

4.5 Automation (Optional)

# PowerShell example to restrict access (requires testing in your environment)
# Get-Acl "C:WindowsSystem32configSAM" | Set-Acl -Access:(("BUILTINUsers","NTFS:Read,Execute"),(("BUILTINAdministrators","FullControl")))...

5. Verification / Validation

• Post-fix check: Run net user as a non-administrator user. Expected output: “System error 5 has occurred. Access is denied.”
• Re-test: Re-run the `net user` command from section 3 to confirm it no longer lists accounts.
• Smoke test: Verify users can still log in and access their normal applications.
• Monitoring: Monitor security logs for failed account enumeration attempts (Event ID 4768, or similar).

net user

6. Preventive Measures and Monitoring

Update security baselines to include restrictions on account enumeration. Implement checks in deployment pipelines.

• Baselines: Update a CIS benchmark or GPO/Intune setting to enforce least privilege access to the SAM database.
• Pipelines: Add static analysis tools (SAST) to check for insecure permissions configurations during build processes.
• Asset and patch process: Review system configurations regularly, at least quarterly, to ensure compliance with security policies.

7. Risks, Side Effects, and Roll Back

Restricting access could impact applications that rely on account enumeration. A roll back involves restoring the original permissions.

• Risk or side effect 2: Incorrectly configured restrictions can prevent legitimate users from accessing resources.
• Roll back: Restore the system snapshot taken in step 4.1, or manually revert permissions changes made in section 4.2.

8. References and Resources

• Vendor advisory or bulletin: Microsoft Security Baselines
• NVD or CVE entry: Not applicable for this general enumeration capability.
• Product or platform documentation relevant to the fix: User Rights Assignment