Cr4sh’s DmaHvBackdoor.c: Hyper-V backdoor for UEFI

Cr4sh is having fun with Windows Device Guard:

DmaHvBackdoor.c comments:

Part of UEFI DXE driver code that injects Hyper-V VM exit handler backdoor into the Device Guard enabled Windows 10 Enterprise. Execution starts from new_ExitBootServices() — a hook handler for EFI_BOOT_SERVICES.ExitBootServices() which being called by winload!OslFwpKernelSetupPhase1(). After DXE phase exit winload.efi transfers exeution to previously loaded Hyper-V kernel (hvix64.sys) by calling winload!HvlpTransferToHypervisor(). To transfer execution to Hyper-V winload.efi uses a special stub winload!HvlpLowMemoryStub() copied to reserved memory page at constant address 0x2000. During runtime phase this memory page is visible to hypervisor core at the same virtual and physical address and has executable permissions which makes it a perfect place to store our Hyper-V backdoor code. VMExitHandler() is a hook handler for VM exit function of hypervisor core, it might be used for interaction between hypervisor backdoor and guest virtual machines.

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Dmytro’s Rogue PCI-E device





scan_thinkpwn: searches for ThinkPwn vulnerability

THINKPWN SCANNER: This program is used to scan UEFI drivers extracted from firmware image for ThinkPwn vulnerability in vendor/model agnostic way.
@d_olex (aka Cr4sh) — initial Vivisect based version of the program;

@trufae (aka pankake) — radare2 based version (this one);

Read the source code for more user docs, including a detailed source comment about how the code works.


More info:


Intel NUC’s Vulnerable to SMM Exploit

A new Intel Security Center advisory:

Intel® Branded NUC’s Vulnerable to SMM Exploit
Intel ID:      INTEL-SA-00057
Product family:      Intel® NUC Kits
Impact of vulnerability:      Elevation of Privilege
Severity rating:      Important
Original release:      Oct 03, 2016
Last revised:      Nov 15, 2016

Intel is releasing updated BIOS firmware for a privilege escalation issue. This issue affects Intel® NUC Kits listed in the affected products section below. The issue identified is a method that enables malicious code to gain access to System Management Mode (SMM). A malicious attacker with local administrative access can leverage the vulnerable BIOS to gain access to System Management Mode (SMM) and take full control of the platform. Intel products that are listed below should apply the update. Intel highly recommends updating the BIOS of all Intel® NUC’s to the recommended BIOS or later listed in the table of affected products. Intel would like to thank Security Researcher Dmytro Oleksiuk for discovering and reporting this issue.




Dmytro takes on the Intel NUC

Dmytro Oleksiuk has a new blog post with UEFI security issues with an Intel NUC using AMI Aptio UEFI BIOS.

(Sad to see that Intel appears to not appear to run CHIPSEC as part of release management QA their own NUCs.)

Exploiting AMI Aptio firmware on example of Intel NUC
[…] Today I’m sharing with you the story of my next x86 machine hacking — we’re going to talk about UEFI vulnerabilities, exploit mitigation features of System Management Mode and new exploit called Aptiocalypsis. Also, this time I did responsible disclosure to Intel and AMI, so, at the moment of this publication you already can patch some of vulnerable products.

Lots of interesting things happened since release of ThinkPwn exploit. Firstly I supposed that vulnerable code was written by Lenovo or its Independent BIOS Vendor (IBV), but later it turned out that they’ve taken this totally mad driver from Intel reference code. This exact code is not available in public, but open source firmware of some Intel boards has it too. For example, SmmRuntimeManagementCallback() function from Intel Quark BSP it’s exactly the same vulnerable code that I’ve found in firmware of my T450s. It’s also interesting that vulnerable code is quite old (it comes from EFI 1.x era) but nevertheless, it was never present in EDK2 source from public repository — its version of QuarkSocPkg was heavily modified in comparison with vulnerable one. The horrible and vulnerable by design piece of code was removed by Intel somewhere in the middle of 2014, but it seems that there were no security advisories regarding this issue. Due to this IBVs had no chance to fix this vulnerability in their relatively old code base and the bug appeared in modern computers from Lenovo, Intel, GIGABYTE, Dell, HP, Fujitsu and other OEM’s (oops!).

Well, I guess at this point it’s much or less clear that currently there’s nothing to do with ThinkPad anymore, it was pwned with 0day, it has too awkward code base that follows ancient version of EFI specification and 8 series chipset that is not the freshest stuff you can get. As my next target for firmware security adventures I’ve decided to take some Skylake based machine of well-known vendor who might have a decent firmware that would be interesting to break. Because I like all kinds of small x86 compatible computers, I’ve put my eye on the latest generation of Intel NUC. It also looks interesting because platform vendor knows his hardware better than anyone else, so, from firmware security perspective, Intel NUC is definitely not the worst choice.[…]




PeiBackdoor: new UEFI payload/backdoor tool

Dmytro Oleksiuk (aka Cr4sh) has created a new UEFI security researcher tool: PeiBackdoor, which hooks into the init code of UEFI. (PEI is the Pre-uEfi-Init phase, before all the UEFI protocols are in place, the init code of UEFI.) It uses Capstone, and requires Windows.

PEI stage backdoor for UEFI compatible firmware

This project implements early stage firmware backdoor for UEFI based firmware. It allows to execute arbitrary code written in C during Pre EFI Init (PEI) phase of Platform Initialization (PI). This backdoor might be useful for low level manipulations with the target platform configuration when the most of the platform configuration registers are not locked yet. […]

PEI backdoor project includes:

* PeiBackdoor.py – Python program that allows to infect raw flash images or individual UEFI PEI drivers with the backdoor code.
* PeiBackdoor_IA32.efi, PeiBackdoor_IA32.pdb – 32-bit PEI backdoor binary compiled with ACTIVE_PLATFORM = IA32.
* PeiBackdoor_X64.efi, PeiBackdoor_X64.pdb – 64-bit PEI backdoor binary compiled with ACTIVE_PLATFORM = X64.
* PeiBackdoor.inf – PEI backdoor project configuration for EDK2 build environment.
* config.h – PEI backdoor build options.
* payload.c – Put your own PEI stage code into this source file and call it from Payload() function.
* src/ – Rest of the PEI backdoor code.

PeiBackdoor.py is using Capstone engine and pefile Python libraries, you need to install them with pip install capstone pefile command.