How to remediate – Windows Registry Enumerate Cached Accounts

1. Introduction

The Windows Registry Enumerate Cached Accounts vulnerability allows retrieval of cached Windows account details stored in registry data. This can provide attackers with a list of potential usernames for brute force attacks or credential stuffing attempts. Systems running Windows are typically affected. A successful exploit could compromise confidentiality by revealing valid user accounts.

2. Technical Explanation

This vulnerability occurs because Windows caches account information in the registry, which can be accessed locally. An attacker with local access can read this data to enumerate potential usernames. There is no specific CVE associated with this general enumeration technique. An example attack involves a script reading the relevant registry keys to extract cached account names.

• Root cause: The Windows operating system stores cached credentials in a readable format within the registry.
• Exploit mechanism: An attacker uses tools like PowerShell or `reg query` to read the cached account list from specific registry locations. For example, running a script to extract usernames from the SAM database cache.
• Scope: All versions of Windows are potentially affected as long as account caching is enabled.

3. Detection and Assessment

Confirming vulnerability involves checking for the presence of cached accounts in the registry. A quick check can verify if the relevant keys exist, while a thorough method involves listing the contents of those keys.

• Quick checks: Use `reg query` to see if the necessary registry keys are present. For example: reg query "HKLMSAMDomainsAccountUsers"
• Scanning: Nessus plugin ID 10384 can identify cached credentials, but results should be verified manually.
• Logs and evidence: Windows Security Event Logs do not directly record registry access for this enumeration activity. Monitoring process creation may show suspicious scripts accessing the SAM database.

reg query "HKLMSAMDomainsAccountUsers"

4. Solution / Remediation Steps

Remediating this vulnerability involves limiting local access and regularly auditing account activity. These steps aim to reduce the risk of credential compromise.

4.1 Preparation

• No services need to be stopped for these actions. A roll back plan involves restoring from backup or using System Restore.
• These changes do not require a specific change window, but should be tested in a non-production environment first.

4.2 Implementation

1. Step 1: Review local administrator accounts and remove any unnecessary ones.
2. Step 2: Implement least privilege access controls to limit user permissions on the SAM database.
3. Step 3: Enable auditing of registry access events (if not already enabled).

4.3 Config or Code Example

Before

reg query "HKLMSAMDomainsAccountUsers" /v F

After

icacls "HKLMSAMDomainsAccountUsers" /grant:r BUILTINAdministrators:(OI)(CI)F

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.

• Practice 1: Least privilege access controls can limit the impact if an attacker gains local access.
• Practice 2: Regular account audits help identify and remove unused or unnecessary accounts.

4.5 Automation (Optional)

# PowerShell example to review local admin accounts
Get-LocalUser | Where-Object {$_.GroupMembership -contains "Administrators"} | Select-Object Name, Enabled

5. Verification / Validation

Confirm the fix by verifying restricted access to registry keys and ensuring no cached accounts are easily enumerable.

• Post-fix check: Run reg query "HKLMSAMDomainsAccountUsers" as a standard user; access should be denied.
• Re-test: Re-run the earlier detection command (reg query "HKLMSAMDomainsAccountUsers") to confirm access is restricted for non-administrators.
• Smoke test: Verify that users can still log in with their existing credentials.
• Monitoring: Monitor Security Event Logs for failed registry access attempts related to the SAM database (Event ID 4663).

reg query "HKLMSAMDomainsAccountUsers"

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 Group Policy settings to enforce least privilege access controls for registry keys.
• Pipelines: Implement regular scans for unnecessary local administrator accounts and excessive permissions.
• Asset and patch process: Review user account activity logs regularly to identify suspicious behaviour.

7. Risks, Side Effects, and Roll Back

• Risk or side effect 1: Incorrectly configured permissions could prevent legitimate applications from accessing necessary registry data.
• Risk or side effect 2: Auditing may generate a large volume of log data, impacting performance.
• Roll back: Restore the registry from backup or use System Restore to revert changes. Revert ICACLS settings if needed.

8. References and Resources

• Vendor advisory or bulletin: Microsoft Local User Account Management Policy
• NVD or CVE entry: No specific CVE is associated with this general enumeration technique.
• Product or platform documentation relevant to the fix: Windows SSH Key Management