Defeating x64: Modern Trends of Kernel-Mode

Rootkits Aleksandr Matrosov

Eugene Rodionov

Who we are?

Malware researchers at ESET- rootkits analysis- development of cleaning tools- tracking new rootkit techniques- investigation of cybercrime

groups

http://www.joineset.com/

Agenda

Evolution of payloads and rootkits Bypassing code integrity checks Attacking Windows Bootloader Modern Bootkit details:

Win64/Olmarik Win64/Rovnix

How to debug bootkit with Bochs emulator

HiddenFsReader as a forensic tool

Evolution of Rootkits

Evolution of Rootkit Installation

exploit payload dropper rootkit

Evolution of Rootkit Installation

Malicious Web-site

ExploitVulnerabili

ty

BypassASLR/DEP

EscapeSandbox

ExecutePayload

DownloadRootkit

EscalateLocal

Privilege

Install RootkitKernel-Mode

Exploit

Dropper

Evolution of Rootkit Features

bypassing HIPS/AV

x86x64

privilege escalation

installing rootkit driver

Rootkit

self-defense

surviving reboot

injecting payload

Rootkit

Rootkit

self-defense

surviving reboot

injecting payload

bypassing signature check

bypassing MS PatchGuard

User

mod

e

Kern

el m

od

e

o Kernel-Mode Code Signing Policy:

It is “difficult” to load unsigned kernel-mode

driver

o Kernel-Mode Patch Protection (Patch Guard):

SSDT (System Service Dispatch Table)

IDT (Interrupt Descriptor Table)

GDT ( Global Descriptor Table)

MSRs (Model Specific Registers)

Obstacles for 64-bit Rootkits

Bypassing Code Integrity Checks

Types of Integrity Checks

o PnP Device Installation Signing Requirements

o Kernel-Mode Code Signing Policy

Enforced on 64-bit version of Windows Vista and later

versions

64-bit Windows Vista and later

32-bit Windows Vista and later

Boot-start driver Non boot-start PnP driver

Non boot-start, non-PnP driver

(except stream

protected media drivers)

Subverting KMCSP

o Abusing vulnerable signed legitimate kernel-

mode driver

o Switching off kernel-mode code signing

checks by altering BCD data:

abusing WinPe Mode

disabling signing check

enabling test signing

o Patching Bootmgr and OS loader

Bypassing Integrity Checks

USER-MODE

Bypassing Integrity Check Techniques

KERNEL-MODE

TESTSIGNING ON

DISABLE INTEGRITY CHECKS

VBR(Volume Boot Record)

System Boot Modification

MBR(Master Boot Record)

Attacking Windows Bootloader

Boot Process

Full KernelInitializati

onMBR

First User-Mode

Process

Kernel ServicesBIOS Services

BIOSInitializati

on

BootLoader

Early Kernel

Initialization

Hardware

CPU in Real Mode CPU in Protected Mode

Load MBR

Load VBR

Load ntldr

Load kernel and boot

start drivers

real mode

real mode

real mode/protected mode

Load MBR

Load VBR

Load bootmgr

Load winload.exe or winresume.exe

real mode

real mode

real mode/protected mode

Load kernel and boot

start drivers

real mode/protected mode

Boot Process of pre Windows Vista OS

Boot Process of post Windows Vista OS

MBR – Master Boot Record

VBR – Volume Boot Record

Boot Process of Windows OS

Boot Process with Bootkit Infection

load malicious MBR/VBR

NT kernel modification

s

load rootkit driver

Code Integrity Check

Bootmgr OS loader OS kernel dependencies

OS kernel

Boot-start drivers

Non boot-start kernel-mode drivers

Evolution of BootkitsStoned

Tequila

Vbootkit

Mebroot

Ol

marik

Evilcore

Rovnix

Stoned

Tequila

Vbootkit

Mebroot

Ol

marik

Evilcore

Rovnix

Stoned

Tequila

Vbootkit

Mebroot

Ol

marik

Evilcore

Rovnix

Stoned

Tequila

Vbootkit

Mebroot

Ol

marik

Evilcore

Rovnix

Stoned

Tequila

Vbootkit

Mebroot

Ol

marik

Evilcore

Rovnix

Stoned

Tequila

Vbootkit

Mebroot

Ol

marik

Evilcore

Rovnix

Stoned

Tequila

Vbootkit

Mebroot

Ol

marik

Evilcore

Rovnix

Stoned

Tequila

Vbootkit

Mebroot

Ol

marik

Evilcore

Rovnix

Stoned

Tequila

Vbootkit

Mebroot

Ol

marik

Evilcore

Rovnix

Stoned

Tequila

Vbootkit

Mebroot

Ol

marik

Evilcore

Rovnix

1987 2007 2010 ?

o Bootkit PoC evolution:

eEye Bootroot (2005)

Vbootkit (2007)

Vbootkit v2 (2009)

Stoned Bootkit (2009)

Evilcore x64 (2011)

2011

o Bootkit Threats evolution:

Win32/Mebroot (2007)

Win32/Mebratix (2008)

Win32/Mebroot v2 (2009)

Win64/Olmarik (2010/11)

Win64/Rovnix (2011)

Win64/Olmarik

Installation on x86 vs. x64

TDL4 Installation on x86

AdjustSeLoadDriver

privilegefail success

Copy itself intoPrintProcessor

director

Check OSversion

Copy itself into%TMP% directory

Set IMAGE_FILE_DLLflag in the PE header

CallDeletePrintProvidorW

API

CallAddPrintProvidorW

API

Vista/Win7

ExploitationMS10-092

successfail

Createmanifest requesting

admin privilege

CallShellExecute

Failinstall

WinXP

TDL4 Installation on x64

Write FS image,patch MBR and Adjust

SE_SHUTDOWN_PRIVILEGEfail success

Copy itself into%TMP% directory

ExploitationMS10-092success

fail

Createmanifest requesting

admin privilege

CallZwRaiseHardError

to create BSOD

Prepare hidden FS image

Report to C&C

Restart Dropper

CallShellExecute

fail

success

BCD

BCD Object1

BCD Element1

BCD Element2

BCD Object2

BCD Element3

Boot Configuration Data (BCD)

BCD Object

Inheritable

Application

Windows boot manager

Windows boot loader

Ntldr

Device

BCD Elements determining KMCSP (before KB2506014)

BCD option Description

BcdLibraryBoolean_DisableIntegrityCheck(0x16000020)

disables kernel-mode code integrity checks

BcdOSLoaderBoolean_WinPEMode (0x26000022)

instructs kernel to be loaded in preinstallation mode, disabling kernel-mode code integrity checks as a byproduct

BcdLibraryBoolean_AllowPrereleaseSignatures(0x16000049)

enables test signing

Abusing Win PE mode: TDL4 modules

Module name Descriptionmbr (infected) infected MBR loads ldr16 module and restores

original MBR in memory

ldr16 hooks 13h interrupt to disable KMCSP and substitute kdcom.dll with ldr32 or ldr64

ldr32 reads TDL4’s kernel-mode driver from hidden file system and maps it into kernel-mode address space

ldr64 implementation of ldr32 module functionality for 64-bit OS

int 13h – service provided by BIOS to communicate with IDE HDD controller

Load infected MBRInfected mbr is

loadedand executed

Load “ldr16” from hidden file system

Hook BIOS int 13h handler and

restore original MBR

“ldr16” is loaded

and executed

Load VBR

Original mbr isloaded

and executed

Load bootmgr

VBR is loaded and executed

read bcd

Bootmgr is loaded and executed

Load winload.exe

Substitute EmsEnabled

option with WinPe

Load ntoskrnl.exe, hal.dll,kdcom.dll,bootvid.dll ant etc

distrort /MININT option

Call KdDebuggerInitialize1 from loaded kdcom.dll

substitute kdcom.dll

with”ldr32” or “ldr64"

Continue kernel initialization

Load ”drv32” or “drv64"

Load bootmgr

Abusing Win PE mode: Workflow

MS Patch (KB2506014)

o BcdOsLoaderBoolean_WinPEMode option no

longer influences kernel-mode code signing

policy

o Size of the export directory of kdcom.dll has

been changed

Bypassing KMCSP: Another Attempt

Patch Bootmgr and OS loader (winload.exe) to

disable KMCSP:

Bypassing KMCSP: Result

Bootmgr fails to verify OS loader’s integrity

MS10-015kills TDL3

TDL4 Hidden File Systems

TDL’s Hidden Storage

o Reserve space in the end of the hard drive (not

visible at file system level analysis)

o Encrypted contents (stream cipher: RC4, XOR-ing)

o Implemented as a hidden volume in the system

o Can be accessed by standard APIs (CreateFile,

ReadFile, WriteFile, SetFilePointer, CloseHandle)

TDL4 Hidden FS

Growth direction

Disk partitions

One sector

One sectorVariable length Not more than 8 Mb

Infe

cted

MBR

TDL4 File System Layout

Debugging Bootkit with WinDbg

WinDbgKDCOM.DLLNTOSKRNL

KD_RECV_CODE_OK

Data packet

Data Packet

KdDebuggerInitialize

KdSendPacket

KdReceivePacket

RETURN_STATUS

WinDbg and kdcom.dll

RETURN_CONTROL

original routine

modified routine

TDL4 and kdcom.dll

TDL4 and kdcom.dll

original export table modified export table

How to Debug TDL4 with WinDbg

o Patch ldr16 to disable kdcom.dll substitution

o Reboot the system and attach to it with WinDbg

o Manually load drv32/drv64

“TDL4 Analysis Paper: a brief introduction and How to Debug It”, Andrea Allievi http://www.aall86.altervista.org/TDLRootkit/TDL4_Analysis_Paper.pdf

Debugging Bootkits with Bochs

•DEMO

Win64/Rovnix

Win64/Rovnix: Installation

Check if already infected

success

fail

Determine OSDigit Capacity

Check OSVersion

Install Corresponding Kernel-mode Driver

Initiate System Reboot

Overwrite Bootstrap Code of Active Partition

Vista/Win7

Check Admin Privileges

success

Windows 2000

Self Delete and Exit

Call ShellExecuteEx API with “runas”

fail

Windows XP

Win64/Rovnix: Bootkit Overview

Load MBR

Load VBR

Load bootmgr

Load winload.exe or winresume.exe

real mode

real mode/protected mode

Load kernel and boot

start drivers

real mode/protected mode

Load bootstrap

code

real mode/protected mode

real mode

Target of Win64\Rovnix

NTFS Bootstrap Code

JMP

[3 b]

Extended BPB

(EBPB)

[48 b]

Signature

[2 b]

Boot Code

[426 b]

OEM ID

[8 b]

BIOS Parameter

Block (BPB)

[25 b]

NTFS Boot Sector (Volume Boot Record)

NTFS Bootstrap Code

Win64/Rovnix: Infected Partition Layout

MBR VBR Bootstrap Code File System Data

VBR Malicious Code File System DataBootstrap

CodeMBR

NTFS bootstrap code(15 sectors)

Before Infecting

After Infecting

Malicious Unsigned

Driver

CompressedData

o Win64/Rovnix overwrites bootstrap code of the active partitiono The malicious driver is written either:

before active partition, in case there is enough space in the end of the hard drive, otherwise

Win64/Rovnix: Bootkit Details

Load MBRMBR is loaded

and executed

Load VBR

Patch bootmgr

VBR is loaded and executed

Read BCD

Restore bootmgr, hook int1 handler and

copy itself over IDT

Load winload.exe

Bootloader parametersare read from BCD

Load ntoskrnl.exe, hal.dll,kdcom.dll,bootvid.dll ant etc

Hook BlImgAllocateImageBuffer

Map malicious driver into kernel-mode address space

Continue kernel initialization

Load malicious bootstrap code

Malicious bootstrap code is

loaded and executed

Hook BIOS int 13h handler and

restore original bootstrap code

Original bootstrap code is restored

Load bootmgrBootmgr is loaded

and receives control

Win64/Rovnix: Loading Unsigned Driver

o Insert malicious driver in BootDriverList of KeLoaderBlock structureo When kernel receives control it calls entry point of each module in the BootDriverListKeLoad

erBlock

BootDriverList

Ntoskrnl.exe

BootDriverList

MaliciousDriver

B o o t D r i v e r L i s t

Win64/Rovnix: Abusing Debugging Facilities

Win64/Rovnix:o hooks Int 1h

tracing handles hardware breakpoints (DR0-DR7)

o overwrites the last half of IDT (Interrupt Descriptor Table) is not used by OS

As a result the malware is able to: set up hooks without patching bootloader

components retain control after switching into protected mode

•DEMO

Olmarik vs Rovnix

Characteristics

Win64/Olmarik Win64/Rovnix

Privilege escalation MS10-092 Reboot technique ZwRaiseHardError API ExitWindowsEx API

MBR/VBR infection MBR VBR (bootstrap code)

Loading driver ZwCreateDriver APIInserting into boot driver

list of KeLoaderBlock structure

Payload injectionKeInitializeApc/

KeInstertQueueApc APIs

KeInitializeApc/KeInstertQueueApc APIs

Self-defense Kernel-mode hooks, MBR monitoring

Number of modules 10 2

Stability of code

Threat complexity

What Facilitates the Attack Vector?

o Untrusted platform problem

BIOS controls boot process, but who controls it?

The trust anchor is below point of attack

Bootmgr OS loader OS kernel dependencies

OS kernel

Boot-start drivers

Non boot-start kernel-mode drivers

Pre boot firmware

Point of Attack

HiddenFsReader as a Forensic Tool

HiddenFsReader as a Forensic Tool

Retrieves content of the malware hidden file system.

Supported malware: TDL3/TDL3+,TDL4;

ZeroAccess (will be added soon)

http://www.youtube.com/watch?v=iRpp6vn2DAE

http://eset.ru/tools/TdlFsReader.exe

HiddenFileReader

User mode

Kernel mode

HiddenFsRecognizer

HiddenFsDecryptor

SelfDefenceDisabler

LowLevelHddReader

HiddenFsReader (HFR) Architecture

Conclusion

The bootkit technique allows malware to bypass KMCSP

Return to old-school techniques of infecting MBR

Win64/Olmarik (TDL4) is the first widely spread rootkit

targeting Win x64

Win64/Rovnix relies on debugging facilities of the

platform to subvert KMCSP

The only possible way of debugging bootkits is to use

emulators (Bochs, QEMU)

The untrusted platform facilitates bootkit techniques

HiddenFsReader is shared amongst malware researchers

References

“The Evolution of TDL: Conquering x64”http://www.eset.com/us/resources/white-papers/The_Evolution_of_TDL.pdf

“Defeating x64: The Evolution of the TDL Rootkit”http://www.eset.com/us/resources/white-papers/TDL4-CONFidence-2011.pdf

“Hasta La Vista, Bootkit: Exploiting the VBR”http://blog.eset.com/2011/08/23/hasta-la-vista-bootkit-exploiting-the-vbr

Follow ESET Threat Bloghttp://blog.eset.com

Questions

Thank you for your attention ;)

Aleksandr Matrosovmatrosov@eset.sk@matrosov

Eugene Rodionovrodionov@eset.sk@vxradius