CVE-2025-21211: Windows 10 1507 Secure Boot Bypass Flaw

CVE-2025-21211 Overview

CVE-2025-21211 is a Secure Boot security feature bypass vulnerability affecting a broad range of Microsoft Windows client and server operating systems. The flaw allows an attacker with physical access to a target device to bypass Secure Boot integrity checks, undermining a foundational platform trust boundary. Microsoft published the advisory on January 14, 2025 as part of its scheduled security update cycle. The issue is tracked under [CWE-693: Protection Mechanism Failure] and impacts confidentiality, integrity, and availability once exploited.

Critical Impact

An attacker who bypasses Secure Boot can load unsigned or tampered boot components, enabling persistent pre-OS malware such as bootkits that survive reinstallation and evade endpoint defenses.

Affected Products

• Microsoft Windows 10 (versions 1507, 1607, 1809, 21H2, 22H2)
• Microsoft Windows 11 (versions 22H2, 23H2, 24H2)
• Microsoft Windows Server 2012, 2016, 2019, 2022, 2022 23H2, and 2025

Discovery Timeline

• 2025-01-14 - CVE-2025-21211 published to NVD by Microsoft
• 2025-01-14 - Microsoft releases security patch via Microsoft CVE-2025-21211 Update Guide
• 2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-21211

Vulnerability Analysis

CVE-2025-21211 resides in the Secure Boot chain of trust that verifies pre-OS components before the Windows kernel loads. Secure Boot is a UEFI feature that cryptographically validates bootloaders, drivers, and firmware to prevent unauthorized code from executing at boot time. When this validation fails, an attacker can substitute a malicious boot image or module that runs before operating system defenses initialize. Because the attack vector is physical, exploitation requires direct interaction with the device, such as attaching removable media or manipulating boot configuration. Once the bypass succeeds, an attacker can achieve high-integrity code execution outside the visibility of the operating system and installed security tooling.

Root Cause

Microsoft categorizes the flaw under [CWE-693: Protection Mechanism Failure], indicating that a control designed to enforce integrity does not fully perform its intended function. The Secure Boot verification path fails to reject a boot artifact that should be treated as untrusted, permitting execution of components outside the signed trust chain. Microsoft has not published low-level implementation specifics, and no public proof-of-concept exists at the time of writing.

Attack Vector

Exploitation requires physical access to the target device with no authentication and no user interaction. A typical attack scenario involves an attacker booting from crafted media, modifying UEFI variables, or replacing components on the EFI System Partition. Successful bypass enables installation of bootkits, unsigned drivers, or firmware implants that persist across operating system reinstalls. Because no public exploit or in-the-wild activity has been reported, and the vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog, immediate mass exploitation risk is limited. The flaw remains relevant for high-value endpoints, kiosks, and devices exposed to evil-maid style scenarios.

No verified proof-of-concept code is publicly available. Refer to the Microsoft CVE-2025-21211 Update Guide for authoritative technical details.

Detection Methods for CVE-2025-21211

Indicators of Compromise

• Unexpected modifications to the EFI System Partition, including new or renamed .efi binaries in \EFI\Microsoft\Boot\ or \EFI\Boot\
• Changes to UEFI variables such as BootOrder, BootXXXX, or Secure Boot policy variables (PK, KEK, db, dbx)
• Unsigned or unknown-publisher bootloaders detected by Measured Boot logs and TPM PCR values that diverge from a known-good baseline

Detection Strategies

• Compare TPM PCR[0]–PCR[7] measurements against a trusted baseline to identify tampering in the Secure Boot chain
• Enable and review Windows Event Log entries under Microsoft-Windows-Kernel-Boot and TPM-WMI for boot integrity anomalies
• Use device health attestation services to validate Secure Boot state on managed endpoints at each check-in

Monitoring Recommendations

• Alert on any process writing to the EFI System Partition or invoking bcdedit.exe with parameters that disable integrity checks or Secure Boot
• Monitor for mountvol.exe or diskpart.exe sessions that mount the system EFI partition outside change windows
• Track physical access events through badge, camera, and console login telemetry correlated with post-boot integrity failures

How to Mitigate CVE-2025-21211

Immediate Actions Required

• Apply the January 2025 Microsoft security update referenced in the Microsoft CVE-2025-21211 Update Guide to all affected Windows and Windows Server systems
• Verify Secure Boot is enabled in UEFI firmware settings and confirm the Secure Boot state via Confirm-SecureBootUEFI in PowerShell
• Set a firmware administrator password to prevent unauthorized changes to boot configuration on physically accessible devices

Patch Information

Microsoft released fixes for CVE-2025-21211 on January 14, 2025 as part of the monthly security update cycle. Patches are available for all supported Windows 10, Windows 11, and Windows Server versions listed in the advisory. Administrators should deploy the cumulative update package appropriate to each affected build and reboot to complete UEFI-related servicing steps.

Workarounds

• Enable BitLocker with TPM and PIN protectors so that boot chain tampering triggers recovery-key prompts before the OS loads
• Restrict physical access to endpoints, servers, and network-connected kiosks using chassis locks, tamper seals, and controlled facilities
• Disable booting from external media (USB, optical, network) in UEFI configuration and lock firmware settings behind a strong administrator password