CVE-2020-0689: Windows 10 Secure Boot Bypass Vulnerability

CVE-2020-0689 Overview

CVE-2020-0689 is a security feature bypass vulnerability in the Microsoft Secure Boot implementation across supported Windows and Windows Server releases. An attacker with high privileges and local access can bypass Secure Boot integrity checks, allowing untrusted code to load during the pre-OS boot sequence. Microsoft published the advisory on February 11, 2020 as part of its monthly security guidance.

The flaw affects Windows 10, Windows 8.1, Windows RT 8.1, Windows Server 2012, Windows Server 2016, and Windows Server 2019. Because the bypass operates below the operating system, it threatens the chain of trust that anti-malware and measured boot controls depend on.

Critical Impact

A successful bypass undermines the Secure Boot trust chain, enabling persistent boot-level implants such as bootkits that survive OS reinstallation and evade endpoint controls.

Affected Products

• Microsoft Windows 10 (versions 1607, 1709, 1803, 1809, 1903, 1909)
• Microsoft Windows 8.1 and Windows RT 8.1
• Microsoft Windows Server 2012, 2012 R2, 2016, and 2019

Discovery Timeline

• 2020-02-11 - Microsoft publishes security advisory for CVE-2020-0689
• 2020-02-11 - CVE-2020-0689 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2020-0689

Vulnerability Analysis

CVE-2020-0689 is classified as a Secure Boot Bypass affecting the Unified Extensible Firmware Interface (UEFI) boot path on Windows systems. Secure Boot is designed to ensure only firmware and OS loaders signed by trusted authorities execute before the kernel initializes. The vulnerability allows an attacker who already holds elevated privileges on the device to subvert these checks and load unsigned or maliciously modified boot components.

The attack vector is local and requires high privileges, but no user interaction. Once the boot chain is compromised, the attacker can achieve high impact to confidentiality, integrity, and availability. The NVD entry does not assign a specific CWE classification, listing it as NVD-CWE-noinfo.

The Exploit Prediction Scoring System (EPSS) rates the likelihood of exploitation at a low probability, and the vulnerability is not present on the CISA Known Exploited Vulnerabilities catalog.

Root Cause

Microsoft has not published detailed root-cause information beyond the advisory text. The flaw resides in the Secure Boot validation logic used by affected Windows builds, where improper enforcement allows a privileged local attacker to circumvent signature or policy verification during boot. See the Microsoft Security Advisory for CVE-2020-0689 for vendor-provided remediation guidance.

Attack Vector

Exploitation requires local access and administrative or SYSTEM-level privileges on the target host. The attacker then introduces a modified boot loader or boot policy that the vulnerable Secure Boot logic fails to reject. On the next reboot, the tampered component executes as part of the trusted boot chain, providing pre-OS persistence and the ability to subvert kernel-mode protections.

No public proof-of-concept code or weaponized exploit is referenced in the NVD data, and the vulnerability is described in prose only as no verified exploitation samples are available.

Detection Methods for CVE-2020-0689

Indicators of Compromise

• Unexpected modifications to UEFI variables such as BootOrder, BootXXXX, or dbx entries that do not correlate with authorized firmware updates.
• Changes to the Windows Boot Manager (bootmgfw.efi) or boot configuration data (BCD) outside of vendor patch cycles.
• Measured Boot logs (TPM PCR values) that diverge from a known-good baseline on otherwise unchanged hardware.

Detection Strategies

• Compare TPM-attested boot measurements against a trusted baseline using Windows Device Health Attestation or an equivalent remote attestation service.
• Monitor administrative actions that touch EFI System Partition contents, bcdedit invocations, or mountvol operations exposing the ESP.
• Correlate privileged process activity with subsequent reboot events to detect potential boot-component tampering workflows.

Monitoring Recommendations

• Enable and forward Windows Event Logs for Code Integrity, BitLocker, and Secure Boot status changes to a centralized analytics platform.
• Track Secure Boot policy version and status (Confirm-SecureBootUEFI) at scale via configuration management tooling.
• Alert on any host reporting Secure Boot disabled or in audit mode where policy requires it enabled.

How to Mitigate CVE-2020-0689

Immediate Actions Required

• Apply the February 2020 Microsoft security update referenced in the advisory to every affected Windows 10, 8.1, RT 8.1, and Windows Server 2012/2016/2019 system.
• Restrict local administrative privileges, since exploitation requires high privileges on the target host.
• Validate Secure Boot is enabled and enforcing on all endpoints and servers that support it.

Patch Information

Microsoft released fixes through its February 11, 2020 security update cycle. Refer to the Microsoft Security Advisory for CVE-2020-0689 for the specific KB articles applicable to each Windows version and apply them through Windows Update, WSUS, or your configuration management platform.

Workarounds

• Enforce least privilege so that standard users cannot acquire administrative or SYSTEM context required for the bypass.
• Enable BitLocker with TPM and PIN protection to bind disk decryption to a measured, trusted boot state.
• Use TPM-based remote attestation to gate network access for devices whose boot integrity cannot be verified.

# Verify Secure Boot status and boot integrity controls on Windows
Confirm-SecureBootUEFI
Get-Tpm
manage-bde -status