1. Introduction
Untrusted Microsoft Office Macro Execution Enabled means a Microsoft Office application allows macros to run without proper security checks. This lets attackers execute malicious code on your systems when opening specially crafted documents. Businesses are at risk of data theft, ransomware, and system compromise. Affected systems include desktops and laptops running Microsoft Office applications like Word, Excel, PowerPoint, and Outlook. A successful attack could lead to loss of confidentiality, integrity, and availability of sensitive information.
2. Technical Explanation
The vulnerability occurs when macro security settings are configured to allow execution of all macros or trust documents from untrusted locations. An attacker can create a malicious document containing VBA code that executes upon opening. This requires the user to open the document, but does not require explicit permission beyond Office’s existing macro permissions.
- Root cause: Incorrectly configured macro security settings in Microsoft Office applications.
- Exploit mechanism: An attacker sends a malicious document (e.g., Word file) to a user. When the user opens the document, the VBA code executes, potentially installing malware or stealing data. For example, a document could contain code that downloads and runs a payload from an external server.
- Scope: Microsoft Office applications including Word, Excel, PowerPoint, Outlook on Windows, macOS, and potentially other platforms depending on Office version.
3. Detection and Assessment
You can check if macro execution is enabled by examining the registry settings or through the Trust Center in Office applications. Scanning tools can also identify this configuration.
- Quick checks: Open any Microsoft Office application, go to File > Options > Trust Center > Trust Center Settings > Macro Settings and verify the current setting.
- Scanning: Nessus plugin ID 6b8542dc can detect untrusted macro execution settings. Other vulnerability scanners may have similar checks.
- Logs and evidence: Windows Event Logs may show events related to macro execution, but these are not always reliable indicators of a vulnerable configuration. Look for event IDs associated with VBA code execution.
reg query "HKCUSoftwareMicrosoftOfficeCommonSecurityMacros" /v MacroOptions 4. Solution / Remediation Steps
Disable the macro execution trust settings to prevent untrusted macros from running. This is best achieved through Group Policy or Intune configuration.
4.1 Preparation
- Dependencies: Administrative privileges are required to modify the registry. Roll back by restoring the registry backup or reverting the Group Policy change.
- A change window may be needed if many users are affected; approval from IT management is recommended.
4.2 Implementation
- Step 1: Open Group Policy Editor (gpedit.msc).
- Step 2: Navigate to User Configuration > Administrative Templates > Microsoft Office
> Security Settings > Macro Settings. - Step 3: Double-click “Disable all macros with notification”.
- Step 4: Select “Enabled” and click OK. This will block all macros except those digitally signed by a trusted publisher.
4.3 Config or Code Example
Before
reg query "HKCUSoftwareMicrosoftOfficeCommonSecurityMacros" /v MacroOptions After
reg query "HKCUSoftwareMicrosoftOfficeCommonSecurityMacros" /v MacroOptions 4.4 Security Practices Relevant to This Vulnerability
Several security practices can help prevent this issue. Least privilege limits the impact of successful attacks, while input validation and safe defaults reduce the attack surface.
- Practice 1: Implement least privilege principles, granting users only the necessary permissions.
- Practice 2: Enforce a strong patch cadence to ensure Office applications are up-to-date with security fixes.
4.5 Automation (Optional)
PowerShell can be used to modify registry settings at scale, but exercise caution when making changes remotely.
# Example PowerShell script (use with caution!)
Set-ItemProperty -Path "HKCU:SoftwareMicrosoftOfficeCommonSecurityMacros" -Name MacroOptions -Value 3 # Disable all macros with notification
5. Verification / Validation
Confirm the fix by checking the macro security settings in Office applications and verifying that untrusted macros are blocked. Test by attempting to open a malicious document.
- Post-fix check: Open any Microsoft Office application, go to File > Options > Trust Center > Trust Center Settings > Macro Settings and verify the setting is “Disable all macros with notification”.
- Re-test: Re-run the registry query from step 3 of Detection and Assessment. The output should reflect the new settings.
- Smoke test: Open a standard Office document (e.g., Word file) to ensure basic functionality remains intact.
- Monitoring: Monitor Windows Event Logs for macro execution events, looking for blocked macros or unexpected VBA activity.
reg query "HKCUSoftwareMicrosoftOfficeCommonSecurityMacros" /v MacroOptions 6. Preventive Measures and Monitoring
Update security baselines to include strict macro settings, and incorporate checks in CI/CD pipelines to prevent insecure configurations. A regular patch review cycle is also important.
- Baselines: Update your security baseline or Group Policy Objects (GPOs) to enforce the “Disable all macros with notification” setting for Microsoft Office applications.
- Pipelines: Add checks in your CI/CD pipeline to ensure that new deployments of Office applications adhere to the secure macro settings configuration.
- Asset and patch process: Implement a monthly patch review cycle to promptly apply security updates for Microsoft Office applications.
7. Risks, Side Effects, and Roll Back
Disabling all macros may break compatibility with legitimate documents that rely on them. Users may need training on how to digitally sign trusted macros. Roll back by reverting the Group Policy change or restoring the registry backup.
- Risk or side effect 1: Some users may experience issues opening older documents that require macros.
- Risk or side effect 2: Users may request exceptions for legitimate macro-enabled documents, requiring careful review and approval.
- Roll back: Step 1: Open Group Policy Editor (gpedit.msc). Step 2: Navigate to User Configuration > Administrative Templates > Microsoft Office
> Security Settings > Macro Settings. Step 3: Double-click “Disable all macros with notification”. Step 4: Select “Not Configured” or “Disabled” and click OK.
8. References and Resources
- Vendor advisory or bulletin: http://www.nessus.org/u?6b8542dc
- NVD or CVE entry: http://www.nessus.org/u?308194e9
- Product or platform documentation relevant to the fix: Microsoft Office Trust Center Documentation.