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Introduction:
In the shadowy realm of Windows security, the boundary between the operating system and the firmware often becomes the last bastion against sophisticated adversaries. The recent development of tools inspired by sl0ppy-UEFIScan highlights a critical shift toward auditing the often-overlooked “legacy” components—specifically driver integrity and Boot Configuration Data (BCD) settings—that can serve as silent entry points for rootkits and bootkits. Understanding how to scan for these vulnerabilities is no longer optional for defenders; it is a necessity in a landscape where attackers increasingly target the boot process to maintain persistence.
Learning Objectives:
- Understand how to manually audit Windows Boot Configuration Data (BCD) for insecure flags that weaken system integrity.
- Learn to verify the digital signatures of critical display drivers and system files using built-in Windows tools.
- Identify the steps required to harden a system against legacy driver exploits and prepare for advanced UEFI Secure Boot checks.
You Should Know:
- Hardening the Boot Chain: Auditing BCD and System Files
The post begins with a scanner that checks the system’s boot mode and flags insecure BCD settings. The presence of flags liketestsigning,nointegritychecks, or `disable-elam` (Early Launch Anti-Malware) can indicate a system that is vulnerable to loading unsigned or malicious drivers. In a secure environment, these should never be active unless for specific debugging scenarios that are tightly controlled.
Step‑by‑step guide to manual BCD auditing and hardening:
To replicate the scanner’s checks manually, an administrator can use the `bcdedit` command from an elevated Command Prompt or PowerShell session.
1. Check Boot Mode:
Confirm-SecureBootUEFI
Or via Command
bcdedit /enum | find "path"
Look for `\Windows\system32\winload.efi` to confirm UEFI mode.
2. Verify Insecure Flags:
bcdedit /enum
Manually inspect the output for the following entries:
– `testsigning` – If set to Yes, the system allows loading of test-signed drivers.
– `nointegritychecks` – If set to Yes, integrity checks for drivers are disabled.
– `disableelamdrivers` – If set to Yes, Early Launch Anti-Malware drivers are disabled.
3. Remediation:
To disable these insecure settings, run:
bcdedit /set testsigning off bcdedit /set nointegritychecks off bcdedit /set disableelamdrivers off
4. System File Integrity Check:
Following the scanner’s recommendation, run the System File Checker and DISM to repair any corrupted or unsigned system files that might have been replaced by malware:
sfc /scannow DISM /Online /Cleanup-Image /RestoreHealth
- Deep Driver Integrity Scanning: Validating Signatures and Mapping Dependencies
The scanner specifically checks `monitor.sys` and notes the absence ofddc.dll. This highlights a crucial aspect of driver integrity: not all drivers are created equal, and missing supporting DLLs can sometimes indicate tampering or misconfiguration. For a robust defense, we must move beyond a simple pass/fail for a single driver and audit the entire loaded driver space.
Step‑by‑step guide to driver signature validation:
Using PowerShell, we can enumerate all loaded drivers and verify their digital signatures. This is a more comprehensive approach than checking individual files.
1. List Loaded Drivers with Signer Information:
Get-WmiObject Win32_SystemDriver | Where-Object {$<em>.State -eq 'Running'} | Select-Object DisplayName, Name, PathName
To get the signature status, use the `Get-AuthenticodeSignature` cmdlet. Here’s a script to iterate through driver paths:
$drivers = Get-WmiObject Win32_SystemDriver | Where-Object {$</em>.State -eq 'Running'}
foreach ($driver in $drivers) {
$path = $driver.PathName.TrimStart('"').TrimEnd('"')
if (Test-Path $path) {
$sig = Get-AuthenticodeSignature $path
Write-Output "$($driver.DisplayName) : $($sig.Status)"
}
}
2. Using `sigcheck` from Sysinternals for Deeper Analysis:
For a more detailed scan that includes hash verification and catalog signing, the Sysinternals `sigcheck` tool is invaluable.
sigcheck -e -nobanner -s C:\Windows\System32\drivers
This command enumerates all drivers in the drivers folder, showing whether they are signed, verified, and the signer details.
3. Linux Equivalent (For UEFI Analysis):
For security professionals working across platforms, verifying UEFI integrity on Linux involves checking the bootloader and Secure Boot status.
Check Secure Boot status sudo mokutil --sb-state List EFI boot entries sudo efibootmgr -v
3. BCD Policy Hardening: Securing the Boot Manager
The initial scanner focuses on BCD for a reason. The Boot Configuration Data store controls the boot process. If an attacker gains write access to this store, they can disable security features or redirect the boot process to a malicious bootloader.
Step‑by‑step guide to BCD hardening and monitoring:
1. Restrict BCD Editing Permissions:
By default, administrators can modify BCD. Consider using Group Policy to restrict who can edit BCD or enable “Secure Boot” customization.
2. Enable Boot Logging and Monitoring:
While not a direct hardening measure, enabling boot logging helps in post-incident analysis.
bcdedit /set {bootmgr} bootlog Yes
The log is stored at `C:\Windows\ntbtlog.txt`.
3. Configure Boot Options for Security:
Ensure that “WinPE” or “Safe Mode” entries do not have debug flags enabled that could be abused.
bcdedit /set {current} safeboot minimal
bcdedit /deletevalue {current} safeboot
4. Implementing UEFI Secure Boot Checks
The author notes that future updates will include more UEFI Secure Boot checks. Secure Boot prevents unsigned code from executing during the boot process. However, it can be misconfigured or disabled. Checking the status and the certificate database is crucial.
Step‑by‑step guide to UEFI Secure Boot validation:
1. Check Secure Boot Status via PowerShell:
Confirm-SecureBootUEFI
A return of `True` indicates Secure Boot is enabled.
2. Verify Secure Boot Policy:
Using the `Get-SecureBootPolicy` cmdlet provides details about the policy applied.
Get-SecureBootPolicy
3. List UEFI Variables (Linux):
For a more forensic approach, especially in dual-boot or compromised environments, Linux tools can dump UEFI variables to check for revoked keys or unknown certificates.
List all UEFI variables ls /sys/firmware/efi/efivars/ Check the Secure Boot variable hexdump -C /sys/firmware/efi/efivars/SecureBoot-
- Automating the Scan: Building Your Own Integrity Scanner
The provided script snippet indicates a custom-built scanner. In a professional environment, building a Python or PowerShell script that combines BCD checks, driver signature validation, and UEFI status checks into a single report is a best practice for ongoing compliance monitoring.
Step‑by‑step guide to building a simple PowerShell integrity scanner:
This script consolidates the checks mentioned above into a single output.
Write-Host " LEGACY & DRIVER INTEGRITY SCANNER " -ForegroundColor Cyan
Check UEFI mode
$env:FIRMWARE_TYPE = (Get-WmiObject -Class Win32_ComputerSystem).SystemType
if ($env:FIRMWARE_TYPE -like "UEFI") {
Write-Host "[bash] System is running in UEFI mode." -ForegroundColor Green
} else {
Write-Host "[bash] System is running in Legacy/BIOS mode." -ForegroundColor Red
}
BCD Check
$bcd = bcdedit /enum
$flags = @("testsigning", "nointegritychecks", "disableelamdrivers")
foreach ($flag in $flags) {
if ($bcd -match $flag) {
Write-Host "[-] '$flag' is ACTIVE." -ForegroundColor Red
} else {
Write-Host "[bash] '$flag' is not active." -ForegroundColor Green
}
}
Driver Check for a specific driver
$driverPath = "$env:windir\System32\drivers\monitor.sys"
if (Test-Path $driverPath) {
$sig = Get-AuthenticodeSignature $driverPath
if ($sig.Status -eq "Valid") {
Write-Host "[bash] OK: monitor.sys is validly signed." -ForegroundColor Green
} else {
Write-Host "[bash] WARNING: monitor.sys signature invalid: $($sig.Status)" -ForegroundColor Red
}
}
What Undercode Say:
- Visibility is the first line of defense: The simple act of scanning for `testsigning` and `nointegritychecks` reveals that many enterprises inadvertently leave these debugging doors open on production systems, creating a massive attack surface for driver-based exploits.
- Legacy isn’t just old hardware; it’s old configurations: The focus on “legacy drivers” underscores a painful truth: the most persistent threats often exploit the oldest, most trusted components in the stack. Driver integrity scanning is not just a compliance exercise but a proactive threat-hunting activity.
- Automation of manual checks is key: While commands like `bcdedit` and `sigcheck` are powerful, they are often run ad-hoc. Integrating these checks into a regular, automated scanning script (like the one inspired by sl0ppy-UEFIScan) ensures that configuration drift—where security settings revert to insecure states—is caught immediately.
Prediction:
As attackers continue to pivot to firmware and driver-level persistence (as seen with advanced rootkits like BlackLotus), we will see a surge in “UEFI scanning” tools integrated directly into EDR and XDR platforms. The future of endpoint security will involve a deeper integration with the Trusted Platform Module (TPM) and Secure Boot, moving beyond simple file-based detection to enforcing cryptographic attestation of the entire boot chain. The work done by developers creating open-source integrity scanners today will lay the foundation for the automated, hardware-anchored security policies of tomorrow.
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IT/Security Reporter URL:
Reported By: Patrick Hoogeveen – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
