CVE-2024-26240
📋 TL;DR
CVE-2024-26240 is a Secure Boot security feature bypass vulnerability that allows attackers to bypass Secure Boot protections and load untrusted or malicious code during the boot process. This affects systems with Secure Boot enabled, primarily Windows devices with UEFI firmware. Attackers could potentially gain elevated privileges and persistence on compromised systems.
💻 Affected Systems
- Windows 10
- Windows 11
- Windows Server 2016
- Windows Server 2019
- Windows Server 2022
📦 What is this software?
Windows 10 1507 by Microsoft
Windows 10 1507 by Microsoft
Windows 10 1607 by Microsoft
Windows 10 1607 by Microsoft
Windows 10 1809 by Microsoft
Windows 10 21h2 by Microsoft
Windows 10 22h2 by Microsoft
Windows 11 21h2 by Microsoft
Windows 11 22h2 by Microsoft
Windows 11 23h2 by Microsoft
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise with persistent malware that survives reboots and reinstalls, enabling attackers to maintain control, steal sensitive data, or deploy ransomware across the network.
Likely Case
Attackers bypass Secure Boot to install bootkits or rootkits that evade detection, maintain persistence, and potentially disable security controls, leading to data theft or lateral movement.
If Mitigated
With proper controls like patching and monitoring, the risk is reduced to isolated incidents that can be detected and contained before significant damage occurs.
🎯 Exploit Status
Exploitation requires physical access or administrative privileges to modify boot configuration. No public proof-of-concept has been released as of the advisory date.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: April 2024 security updates (KB5036893 for Windows 10, KB5036892 for Windows 11, etc.)
Vendor Advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2024-26240
Restart Required: Yes
Instructions:
1. Apply the April 2024 security updates from Windows Update. 2. For enterprise environments, deploy updates via WSUS, Configuration Manager, or Microsoft Intune. 3. Restart systems to complete installation.
🔧 Temporary Workarounds
Disable Secure Boot
windowsTemporarily disable Secure Boot in UEFI firmware settings to prevent exploitation, though this reduces security.
Enable BitLocker with TPM
windowsEnable BitLocker with TPM protection to detect unauthorized boot modifications, though this doesn't prevent the bypass.
manage-bde -on C: -usedpacealways
🧯 If You Can't Patch
- Restrict physical access to vulnerable systems and implement strict administrative privilege controls.
- Monitor for unexpected boot configuration changes or Secure Boot policy modifications using security tools.
🔍 How to Verify
Check if Vulnerable:
Check if Secure Boot is enabled via 'Confirm-SecureBootUEFI' in PowerShell, and verify Windows version is before April 2024 updates.Check Version:
wmic os get caption, version, buildnumberVerify Fix Applied:
Verify the April 2024 security update is installed via 'Get-Hotfix -Id KB5036893' (adjust KB number for your OS) and confirm Secure Boot status is still enabled.📡 Detection & Monitoring
Log Indicators:
- Event ID 1015 from 'Microsoft-Windows-SecureBoot' with failures or policy changes
- Unexpected modifications to boot configuration in System logs
Network Indicators:
- Unusual outbound connections from systems during boot process
- Anomalous network traffic patterns post-reboot
SIEM Query:
EventID=1015 AND Source='Microsoft-Windows-SecureBoot' | search 'failure' OR 'policy change'