CVE-2024-26194 Overview
CVE-2024-26194 is a Secure Boot security feature bypass vulnerability affecting multiple versions of Microsoft Windows and Windows Server. The flaw allows a local attacker with the ability to execute code during the boot process to bypass Secure Boot integrity checks. Successful exploitation undermines the chain of trust established by Unified Extensible Firmware Interface (UEFI) Secure Boot, enabling the loading of unsigned or malicious pre-boot components. Microsoft classifies the issue under [CWE-347] Improper Verification of Cryptographic Signature. The vulnerability requires local access and high attack complexity, but it can lead to full compromise of confidentiality, integrity, and availability.
Critical Impact
An attacker who bypasses Secure Boot can execute pre-OS code such as bootkits, persist beneath the operating system, and evade endpoint defenses that rely on a trusted boot chain.
Affected Products
- Microsoft Windows 10 (1507, 1607, 1809, 22H2) on x86 and x64
- Microsoft Windows 11 23H2
- Microsoft Windows Server 2008, 2012, 2016, 2019, 2022, and 2022 23H2
Discovery Timeline
- 2024-04-09 - CVE-2024-26194 published to the National Vulnerability Database (NVD)
- 2024-04-09 - Microsoft releases security update addressing the Secure Boot bypass
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2024-26194
Vulnerability Analysis
CVE-2024-26194 exists in the Windows Secure Boot implementation, which validates the cryptographic signatures of firmware and bootloader components before execution. The flaw allows an attacker with local privileges to bypass this signature verification and load code that Secure Boot would otherwise reject. Because the compromise occurs at the pre-boot stage, malicious payloads execute with the highest privilege on the machine and persist before Windows kernel protections initialize.
The vulnerability is mapped to CWE-347, indicating that a component of the boot verification process fails to properly validate a cryptographic signature. Attackers typically chain this class of flaw with physical access or an existing foothold that permits writing to the EFI System Partition or modifying boot configuration data.
Root Cause
The root cause is improper verification of cryptographic signatures during the Secure Boot sequence. A signed component or boot policy is trusted without adequate validation, letting an attacker substitute or tamper with binaries that Secure Boot should reject. Microsoft has not published low-level technical details in its advisory.
Attack Vector
Exploitation requires local access to the target system. An attacker with sufficient permissions can stage crafted boot artifacts, reboot the machine, and cause the pre-OS environment to load unverified code. The high attack complexity reflects the need for prior access, precise environmental conditions, or specialized boot-time artifacts. No public proof-of-concept exploit is available, and the CVE is not listed on the CISA Known Exploited Vulnerabilities (KEV) catalog.
No verified exploitation code is available for this vulnerability. Refer to the Microsoft CVE-2024-26194 Advisory for vendor-provided details.
Detection Methods for CVE-2024-26194
Indicators of Compromise
- Unexpected modifications to the EFI System Partition, including new or altered .efi binaries
- Boot Configuration Data (BCD) changes referencing unsigned or unknown bootloaders
- Measured Boot logs (TCG event logs) showing PCR values that diverge from a known-good baseline
- Presence of revoked or unusual bootloaders not consistent with the vendor image
Detection Strategies
- Compare current Measured Boot and TPM PCR values against a trusted baseline captured on a known-clean system
- Monitor Windows Defender System Guard and Device Health Attestation reports for boot integrity failures
- Audit changes to \EFI\Microsoft\Boot\ and other UEFI-related paths using file integrity monitoring
- Alert on execution of bcdedit.exe with parameters that disable integrity checks or modify boot policy
Monitoring Recommendations
- Centralize boot attestation telemetry from endpoints and correlate deviations across the fleet
- Track KB update deployment status to confirm affected Windows and Windows Server hosts receive the April 2024 patches
- Review privileged local sessions preceding reboots on servers and administrator workstations
How to Mitigate CVE-2024-26194
Immediate Actions Required
- Apply the Microsoft security updates released for CVE-2024-26194 to all affected Windows and Windows Server systems
- Prioritize domain controllers, hypervisors, and systems holding sensitive credentials or keys
- Restrict local administrator access and enforce least privilege to reduce the population of users who can stage a pre-boot attack
- Enable TPM-backed BitLocker and measured boot attestation to detect tampering with the boot chain
Patch Information
Microsoft addressed CVE-2024-26194 in the April 2024 security update cycle. Refer to the Microsoft CVE-2024-26194 Advisory for the specific KB numbers matching each affected Windows and Windows Server build.
Workarounds
- Enforce full-disk encryption with BitLocker tied to TPM and PIN to raise the bar for pre-boot tampering
- Disable legacy boot paths and require UEFI with Secure Boot enabled in firmware settings
- Physically secure endpoints and servers, and use chassis intrusion detection where available
- Apply the Secure Boot DBX revocation list updates published by Microsoft to block known-bad bootloaders
# Verify Secure Boot status and boot integrity on Windows
Confirm-SecureBootUEFI
Get-Tpm
Get-BitLockerVolume
# Review measured boot log for unexpected components
Get-WinEvent -LogName Microsoft-Windows-Kernel-Boot/Operational
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
