CVE-2026-41097

What it actually does

CVE-2026-41097 is a local Windows Secure Boot security feature bypass caused by reliance on a boot component that cannot be reliably updated or revoked in the normal Secure Boot trust chain. An attacker who already has high local privileges can abuse the trusted-but-unupdateable component during the pre-boot or early boot process to bypass Secure Boot protections, potentially allowing unauthorized boot code, kernel tampering, or malicious drivers to run before Windows security controls are fully active. The CVSS vector indicates local access, low attack complexity, high privileges required, no user interaction, and high confidentiality, integrity, and availability impact.

Why it matters to the business

Successful exploitation can undermine the trust foundation of Windows endpoints and servers, enabling stealthy persistence below the operating system, weakening endpoint security controls, and increasing the difficulty of incident response or system recovery. Because exploitation requires an already highly privileged local attacker and there is no known exploitation, KEV listing, ransomware association, or public exploit maturity reported, the near-term mass exploitation risk appears lower than internet-facing remote vulnerabilities; however, the impact is serious on systems where attackers have already obtained administrator or equivalent control. The affected scope includes multiple supported Windows 10, Windows 11, Windows Server 2019, Windows Server 2022, and Windows Server 2025 releases, so enterprises should treat this as an important hardening and patch management issue across workstation and server fleets.

How an attack unfolds

An attacker first gains high-privilege local access to an affected Windows system through separate means, such as stolen administrator credentials, privilege escalation, remote management misuse, or prior malware execution. With that level of control, the attacker targets the boot environment rather than a normal user-mode application. They abuse the trusted, non-updateable Secure Boot component to introduce or execute boot-stage code that would normally be blocked by Secure Boot policy. On reboot, the manipulated boot path allows the attacker-controlled code to run before Windows has fully initialized protections such as code integrity, endpoint detection, credential protections, or kernel security boundaries. From there, the attacker may load unsigned or malicious kernel components, hide artifacts, disable security controls, maintain persistence across reboots, or prepare the host for credential theft, data access, destructive activity, or lateral movement. No named threat actors or active exploitation campaigns were provided for this CVE, and the EPSS score is low and flat over the last 30 days, but Secure Boot bypasses are attractive post-compromise capabilities for advanced intrusions.

How to fix it

Apply the latest Microsoft security updates and cumulative updates for all affected Windows versions, including Windows 10 1809, 21H2, 22H2; Windows 11 23H2, 24H2, 25H2, 26H1; Windows Server 2019; Windows Server 2022; Windows Server 2022 23H2; and Windows Server 2025. No exact fixed version list was provided, so remediation should be validated against Microsoft’s official security update guidance for this CVE and the applicable monthly update baseline. Ensure Secure Boot remains enabled, install available UEFI firmware updates from hardware vendors, and apply Secure Boot DB/DBX revocation updates when Microsoft or OEM guidance requires them. Restrict local administrator rights, protect remote management paths, enforce credential hygiene, and monitor or block unauthorized changes to the EFI System Partition and boot configuration. Where immediate patching is not possible, reduce exposure by limiting administrator access, enabling BitLocker with TPM protection, enforcing EDR tamper protection, and increasing monitoring for boot configuration and firmware-related changes.

How to confirm the fix worked

Confirm affected systems have received the applicable Microsoft cumulative or security update for the relevant Windows release using enterprise patch tooling, Windows Update history, Get-HotFix, or equivalent inventory data. Verify Secure Boot is enabled with Confirm-SecureBootUEFI, msinfo32, or firmware management tooling. Review boot configuration with bcdedit /enum all and confirm test signing, kernel debugging, boot debugging, and integrity bypass options are not enabled unless explicitly approved. Check that the EFI System Partition does not contain unexpected bootloaders, recently modified boot files, or unauthorized vendor boot entries. Validate that BitLocker protection is active where required and that unexpected BitLocker recovery events did not occur after patching. For servers and high-value endpoints, perform at least one controlled reboot after patching to confirm normal boot, Secure Boot state, EDR health, and absence of boot integrity alerts.

Typical attack path

1. Obtain local high-privilege access to an affected Windows endpoint or server.
2. Enumerate Secure Boot, firmware, BitLocker, boot configuration, and EFI System Partition state.
3. Modify or stage boot-related components, boot configuration, or EFI artifacts needed to exercise the Secure Boot bypass.
4. Reboot or otherwise trigger the vulnerable boot path.
5. Use the bypass to run code that Secure Boot would normally prevent.
6. Load malicious or unsigned kernel-level components, tamper with operating system protections, or establish low-level persistence.
7. Use the compromised host for stealth, credential access, lateral movement, data access, or further destructive operations.

How to detect it

To determine whether exploitation may have already occurred, focus on evidence of boot-chain tampering and post-compromise activity rather than a single definitive exploit signature. Collect Windows System, Security, Code Integrity, Kernel-Boot, BitLocker, and Defender/EDR telemetry. Review command execution logs, PowerShell logs, Sysmon events, and EDR process telemetry for bcdedit, mountvol, diskpart, reagentc, bootsect, and direct access to the EFI System Partition. Look for Secure Boot being disabled, test signing or integrity checks being disabled, boot debugging being enabled, unexpected bootloader files, unusual modifications under EFI paths, unsigned or anomalous kernel driver loads, EDR tamper events, and BitLocker recovery triggers. Correlate these artifacts with prior local administrator logons, remote management sessions, credential use, or malware activity. Because the input reports no known exploitation or public exploit maturity, absence of these indicators does not prove safety, but their presence should trigger incident response and boot-chain integrity validation.

• bcdedit /set testsigning on
• bcdedit /set {default} testsigning on
• bcdedit /set nointegritychecks on
• bcdedit /set {default} nointegritychecks on
• bcdedit /set debug on
• bcdedit /set bootdebug on
• bcdedit /set recoveryenabled no
• bcdedit /set {bootmgr} bootdebug on
• Confirm-SecureBootUEFI : False
• Secure Boot State: Off
• \EFI\Microsoft\Boot\bootmgfw.efi
• \EFI\Boot\bootx64.efi
• \EFI\Microsoft\Boot\BCD
• mountvol /s
• mountvol S: /s
• diskpart
• select partition system
• assign letter=
• Microsoft-Windows-Kernel-Boot
• Microsoft-Windows-CodeIntegrity
• Microsoft-Windows-BitLocker-API
• Code Integrity determined that a process
• The boot configuration data store could not be opened
• BitLocker recovery
• testsigning Yes
• nointegritychecks Yes
• bootdebug Yes
• debug Yes

What your security team should do

• Prioritize patching high-value servers, administrator workstations, domain administration endpoints, security tooling servers, and systems used for remote management.
• Confirm Microsoft’s official advisory for this CVE and deploy the relevant Windows cumulative/security updates through the normal enterprise patch channel.
• Keep Secure Boot enabled and verify that policy, firmware, and boot configuration have not been weakened on affected Windows systems.
• Review and reduce local administrator membership, especially on endpoints where broad administrative access is granted to users or support tools.
• Monitor for suspicious EFI System Partition writes, bcdedit changes, Secure Boot state changes, unsigned driver loading, and unexpected BitLocker recovery events.
• Ensure EDR tamper protection, Windows Defender Application Control or equivalent application control, and driver block rules are enabled where operationally feasible.
• For any system with suspected boot-chain tampering, prefer full forensic acquisition and trusted-media recovery or reimaging over in-place cleanup.
• Track EPSS and KEV status for changes; although current EPSS is low and this is not listed in KEV, Secure Boot bypasses can become more urgent if proof-of-concept tooling or actor use emerges.