Microsoft Security Bulletin MS16-100 - Important

Security Update for Secure Boot (3179577)

Published: August 9, 2016

Version: 1.0

Executive Summary

This security update resolves a vulnerability in Microsoft Windows. The vulnerability could allow security feature bypass if an attacker installs an affected boot manager and bypasses Windows security features.

This security update is rated Important for all supported editions of Windows 8.1, Windows Server 2012, Windows Server 2012 R2, Windows RT 8.1, and Windows 10. For more information, see the Affected Software and Vulnerability Severity Ratings section.

The security update addresses the vulnerability by blacklisting affected boot managers. For more information about the vulnerability see the Vulnerability Information section.

For more information about this update, see Microsoft Knowledge Base Article 3179577.

Affected Software and Vulnerability Severity Ratings

The following software versions or editions are affected. Versions or editions that are not listed are either past their support life cycle or are not affected. To determine the support life cycle for your software version or edition, see Microsoft Support Lifecycle.

The following severity ratings assume the potential maximum impact of the vulnerability. For information regarding the likelihood, within 30 days of this security bulletin's release, of the exploitability of the vulnerability in relation to its severity rating and security impact, please see the Exploitability Index in the Aug bulletin summary.

**Operating System** [**Secure Boot Security Feature Bypass Vulnerability – CVE-2016-3320**](http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=cve-2016-3320) **Updates Replaced**\*
**Windows 8.1**
[Windows 8.1 for 32-bit Systems](http://www.microsoft.com/downloads/details.aspx?familyid=19c5ba0d-de7b-41af-8db3-76d1ff6f79b2) (3172729) **Important**  Security Feature Bypass None
[Windows 8.1 for x64-based Systems](http://www.microsoft.com/downloads/details.aspx?familyid=e0aedb91-f808-4ae8-86f4-46015f6b7c0b) (3172729) **Important**  Security Feature Bypass None
**Windows Server 2012 and Windows Server 2012 R2**
[Windows Server 2012](http://www.microsoft.com/downloads/details.aspx?familyid=224b85dd-5caf-4c9f-852f-88f2542f9a94) (3172729) **Important**  Security Feature Bypass None
[Windows Server 2012 R2](http://www.microsoft.com/downloads/details.aspx?familyid=14f74104-ff9e-4fe6-8bd0-2b749afb3171) (3172729) **Important**  Security Feature Bypass None
**Windows RT 8.1**
Windows RT 8.1[1] (3172729) **Important**  Security Feature Bypass None
**Windows 10**
[Windows 10 for 32-bit Systems](https://support.microsoft.com/kb/3172729)[2] (3172729) **Important**  Security Feature Bypass None
[Windows 10 for x64-based Systems](https://support.microsoft.com/kb/3172729)[2] (3172729) **Important**  Security Feature Bypass None
[Windows 10 Version 1511 for 32-bit Systems](https://support.microsoft.com/kb/3172729)[2] (3172729) **Important**  Security Feature Bypass None
[Windows 10 Version 1511 for x64-based Systems](https://support.microsoft.com/kb/3172729)[2] (3172729) **Important**  Security Feature Bypass None
**Server Core installation option**
[Windows Server 2012](http://www.microsoft.com/downloads/details.aspx?familyid=224b85dd-5caf-4c9f-852f-88f2542f9a94) (Server Core installation) (3172729) **Important**  Security Feature Bypass None
[Windows Server 2012 R2](http://www.microsoft.com/downloads/details.aspx?familyid=14f74104-ff9e-4fe6-8bd0-2b749afb3171) (Server Core installation) (3172729) **Important**  Security Feature Bypass None
[1]This update is only available via [Windows Update](http://go.microsoft.com/fwlink/?linkid=21130).

[2]Windows 10 updates are cumulative. The monthly security release includes all security fixes for vulnerabilities that affect Windows 10, in addition to non-security updates. The updates are available via the Microsoft Update Catalog.

*The Updates Replaced column shows only the latest update in any chain of superseded updates. For a comprehensive list of updates replaced, go to the Microsoft Update Catalog, search for the update KB number, and then view update details (updates replaced information is provided on the Package Details tab).

Note The vulnerability discussed in this bulletin affects Windows Server 2016 Technical Preview 5. To be protected from the vulnerability, Microsoft recommends that customers running this operating system apply the current update, which is available from Windows Update

Vulnerability Information

Secure Boot Security Feature Bypass Vulnerability – CVE-2016-3320

A security feature bypass vulnerability exists when Windows Secure Boot improperly loads a boot manager that is affected by the vulnerability. An attacker who successfully exploited this vulnerability could disable code integrity checks, allowing test-signed executables and drivers to be loaded onto a target device. Furthermore, the attacker could bypass Secure Boot Integrity Validation for BitLocker and Device Encryption security features.

To exploit the vulnerability, an attacker who has gained administrative privileges or who has physical access to a target device could install an affected boot manager.The security update addresses the vulnerability by blacklisting affected boot managers.

The following table contains links to the standard entry for each vulnerability in the Common Vulnerabilities and Exposures list:

Vulnerability title CVE number Publicly disclosed Exploited
Secure Boot Security Feature Bypass Vulnerability CVE-2016-3320 No No
### Mitigating Factors The following [mitigating factors](https://technet.microsoft.com/library/security/dn848375.aspx) may be helpful in your situation: - To exploit the vulnerability, an attacker must have either administrative privileges or physical access to the target device. ### Workarounds The following [workarounds](https://technet.microsoft.com/library/security/dn848375.aspx) may be helpful in your situation: - **Configure BitLocker to use Trusted Platform Module (TPM)+PIN protection** To enable TPM and PIN protector, enable the enhanced protection group policy as follows: 1. Click **Start**, click **Run**, type **gpedit.msc**, and then click **OK** to open the Local Group Policy Editor. 2. Under **Local Computer Policy**, navigate to Administrative Templates>Windows Components>BitLocker Drive Encryption>Operating Systems Drives. 3. In the right-hand pane, double-click **Require additional authentication at startup**. 4. In the dialog box that appears, click **Enabled**. 5. Under **Options**, select **Require TPM** and **Require startup PIN with TPM**. 6. Click **Apply** and exit the Local Group Policy Editor. 7. Open the command prompt with Administrator privileges. 8. Enter the following command: ``` manage-bde -protectors -add c: -tpmandpin ``` 9. When prompted for a PIN, enter a 4 or 6-digit PIN. 10. Restart the system. **Impact of workaround. ** The user will be required to enter the PIN every time the computer restarts. **How to undo the workaround** 1. Click **Start**, click **Run**, type **gpedit.msc**, and then click **OK** to open the Local Group Policy Editor. 2. Under **Local Computer Policy**, navigate to Administrative Templates>Windows Components>BitLocker Drive Encryption>Operating Systems Drives 3. In the right-hand pane, double-click “Require additional authentication at startup” 4. In the dialog box that appears, click **Enabled**. 5. Under Options, select Allow TPM and Allow startup PIN with TPM. 6. Click **Apply** and exit the Local Group Policy Editor. 7. Restart the system.   - **Disable Secure Boot integrity protection of BitLocker** To disable Secure Boot, you must follow each of the steps in order. 1. Disable BitLocker 1. Open **Control Panel** and then click **BitLocker Drive Encryption.** 2. Click **Turn off BitLocker** 3. In the **BitLocker Drive Encryption** dialog box, click **Turn off BitLocker**. 4. Exit **Control Panel**. 2. Disable Secure Boot 1. Click **Start**, click **Run**, type **gpedit.msc**, and then click **OK** to open the Local Group Policy Editor. 2. Under **Local Computer Policy**, navigate to Administrative Templates>Windows Components>BitLocker Drive Encryption>Operating Systems Drives 3. Double-click **Allow Secure Boot for integrity validation**. 4. In the dialog box that appears, click **Disabled**. 5. Click **Apply** and exit the Local Group Policy Editor. 3. Re-enable BitLocker 1. Open **Control Panel**, then click **BitLocker Drive Encryption.** 2. Click **Turn on BitLocker** 3. In the **BitLocker Drive Encryption** dialog box, click **Turn on BitLocker**. 4. Exit **Control Panel**. **Impact of workaround.**  Disabling Secure Boot may cause systems to enter BitLocker recovery mode more often when you update firmware versions or BCD settings. **How to undo the workaround.**  1. Disable BitLocker 1. Open **Control Panel**, then click **BitLocker Drive Encryption.** 2. Click **Turn off BitLocker** 3. In the **BitLocker Drive Encryption** dialog box, click **Turn off BitLocker**. 4. Exit **Control Panel**. 2. Enable Secure Boot 1. Click **Start**, click **Run**, type **gpedit.msc**, and then click **OK** to open the Local Group Policy Editor. 2. Under **Local Computer Policy**, navigate to Administrative Templates>Windows Components>BitLocker Drive Encryption>Operating Systems Drives 3. Double-click **Allow Secure Boot for integrity validation**. 4. In the dialog box that appears, click **Enabled**. 5. Click **Apply** and exit the Local Group Policy Editor. 3. Re-enable BitLocker 1. Open **Control Panel**, then click **BitLocker Drive Encryption.** 2. Click **Turn on BitLocker** 3. In the **BitLocker Drive Encryption** dialog box, click **Turn on BitLocker**. 4. Exit **Control Panel**. Security Update Deployment -------------------------- For Security Update Deployment information, see the Microsoft Knowledge Base article referenced [here](https://technet.microsoft.com/en-us/library/%5c%5c%5cc(v=Security.10)) in the Executive Summary. Acknowledgments --------------- Microsoft recognizes the efforts of those in the security community who help us protect customers through coordinated vulnerability disclosure. See [Acknowledgments](https://technet.microsoft.com/library/security/mt674627.aspx) for more information. Disclaimer ---------- The information provided in the Microsoft Knowledge Base is provided "as is" without warranty of any kind. Microsoft disclaims all warranties, either express or implied, including the warranties of merchantability and fitness for a particular purpose. In no event shall Microsoft Corporation or its suppliers be liable for any damages whatsoever including direct, indirect, incidental, consequential, loss of business profits or special damages, even if Microsoft Corporation or its suppliers have been advised of the possibility of such damages. Some states do not allow the exclusion or limitation of liability for consequential or incidental damages so the foregoing limitation may not apply. Revisions --------- - V1.0 ([August 9, 2016](https://technet.microsoft.com/en-us/library/bulletin_publisheddate(v=Security.10))): Bulletin published. *Page generated 2016-08-09 12:52-07:00.*