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MicrosoftKB4535680

HistoryFeb 11, 2020 - 8:00 a.m.

KB4535680: Security update for Secure Boot DBX: January 12, 2021

2020-02-1108:00:00

Microsoft

support.microsoft.com

163

6.7 Medium

CVSS3

Attack Vector

LOCAL

Attack Complexity

LOW

Privileges Required

HIGH

User Interaction

NONE

Scope

UNCHANGED

Confidentiality Impact

HIGH

Integrity Impact

HIGH

Availability Impact

HIGH

CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H

6.9 Medium

AI Score

Confidence

High

4.6 Medium

CVSS2

Access Vector

LOCAL

Access Complexity

LOW

Authentication

NONE

Confidentiality Impact

PARTIAL

Integrity Impact

PARTIAL

Availability Impact

PARTIAL

AV:L/AC:L/Au:N/C:P/I:P/A:P

0.0004 Low

EPSS

Percentile

8.8%

JSON

KB4535680: Security update for Secure Boot DBX: January 12, 2021

IMPORTANT This article is superseded by KB5012170: Security update for Secure Boot DBX.

Applies to

This security update applies only to the following Windows versions:

Windows Server 2012 x64-bit
Windows Server 2012 R2 x64-bit
Windows 8.1 x64-bit
Windows Server 2016 x64-bit
Windows Server 2019 x64-bit
Windows 10, version 1607 x64-bit
Windows 10, version 1803 x64-bit
Windows 10, version 1809 x64-bit
Windows 10, version 1909 x64-bit

Summary

This security update makes improvements to Secure Boot DBX for the supported Windows versions listed in the “Applies to” section. Key changes include the following:

Windows devices that has Unified Extensible Firmware Interface (UEFI) based firmware can run with Secure Boot enabled. The Secure Boot Forbidden Signature Database (DBX) prevents UEFI modules from loading. This update adds modules to the DBX.

A security feature bypass vulnerability exists in secure boot. An attacker who successfully exploited the vulnerability might bypass secure boot and load untrusted software.

This security update addresses the vulnerability by adding the signatures of the known vulnerable UEFI modules to the DBX.
To learn more about this security vulnerability, see CVE-2020-0689 | Microsoft Secure Boot Security Feature Bypass Vulnerability.

Known issues

Issue	Workaround
Some original equipment manufacturer (OEM) firmware might not allow for the installation of this update.	To resolve this issue, contact your firmware OEM.
If BitLocker Group Policy Configure TPM platform validation profile for native UEFI firmware configurations is enabled and PCR7 is selected by policy, it may result in the BitLocker recovery key being required on some devices where PCR7 binding is not possible.To view the PCR7 binding status, run the Microsoft System Information (Msinfo32.exe) tool with administrative permissions.	To workaround this issue, do one of the following based on credential guard configuration before you deploy this update:

On a device that does not have Credential Gard enabled, run following command from an Administrator command prompt to suspend BitLocker for 1 reboot cycle:`

Manage-bde –Protectors –Disable C: -RebootCount 1

`
Then, restart the device to resume the BitLocker protection.

Note Do not enable BitLocker protection without additionally restarting the device as it would result in BitLocker recovery.

On a device that has Credential Guard enabled, there may be multiple restarts during the update that require BitLocker to be suspended. Run the following command from an Administrator command prompt to suspend BitLocker for 3 restart cycles. Manage-bde –Protectors –Disable C: -RebootCount 3This update is expected to restart the system two times. Restart the device once again to resume the BitLocker protection.Note Do not enable BitLocker protection without additionally restarting as it would result in BitLocker recovery.
You might enter Bitlocker recovery if conflicting BitLocker group policy settings are configured after BitLocker has been enabled in environment. Bitlocker recovery can be triggered due to any of the below Group Policy settings:
Forcing Explicit configuration of PCR bindings that is different from what is already chosen by BitLocker.
Configuring GP “Allow Secure Boot for integrity validation” to dis-allow Secure boot for integrity validation but BitLocker is already using secure boot (PCR7).
Configuring Group Policy to Require additional Authentication during startup but BitLocker has been configured before deploying this group policy.
| If this update has already been applied and the device hasn’t restarted, suspend BitLocker and restart after following the below steps:
If an explicit PCR configuration has been set through group policy or a policy is configured to disallow using secure boot for integrity validation, Suspend and resume BitLocker to clear the GP conflicts.
If the Require additional Authentication during startup policy is configured to require TPM and PIN, run the following command from an Administrative command prompt and enter the desired PIN: manage-bde -protectors -add c: -TPMAndPin * If the Require additional Authentication during startup policy is configured to require a startup key, execute the following command to create startup key:manage-bde -protectors -add c: -tpmandstartupkey <path to external key directory> * If the Require additional Authentication during startup policy is configured to require startup key and pin, execute the following command from Admin command prompt to create Pin and startup key. When prompted, enter the desired PIN:**manage-bde -protectors -add c: **-tpmandpinandstartupkey <path to external key directory>
This update might not install on devices with an unsigned, non-Microsoft bootx64.efi boot manager file. This update might be offered and reoffered through Windows Update but might not install. When you try to install this update manually, you might receive an error, “Some updates were not installed” listing KB4565680. You can also check the CBS Log file in %systemroot%\logs\cbs for the following error: onecore\base\secureboot\servicing\advancedinstaller\securebootai.cpp(277): Error TRUST_E_NOSIGNATURE originated in function Windows::WCP::SecureBoot::BasicInstaller::Install expression: ApplySecureBootUpdate( dwAvailableUpdates)| We are working on a resolution and estimate a solution will be available for Windows 10, version 1909, Windows 10, version 2004 and Windows 10, version 20H2 in late March. The remaining supported versions of Windows are estimated to have a solution available in mid-April.For additional guidance before the release of the resolution, please contact your device manufacturer (OEM).

How to get this update

Method 1: Windows Update

This update is available through Windows Update. It will be downloaded and installed automatically.

Method 2: Microsoft Update Catalog

To get the stand-alone package for this update, go to the Microsoft Update Catalog website.

Method 3: Windows Server Update Services

This update is also available through Windows Server Update Services (WSUS).

Prerequisites

Make sure you have the lastest servicing stack update (SSU) installed. For information about the latest SSU for your operating system, see ADV990001 | Latest Servicing Stack Updates.

Restart information

Your device does not have to restart when you apply this update. If you have Windows Defender Credential Guard (Virtual Secure Mode) enabled, your device will restart two times.

Update replacement information

This update does not replace any previously released update.