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Core Security Technologies - CoreLabs Advisory
http://www.coresecurity.com/corelabs/
Sun xVM VirtualBox Privilege Escalation Vulnerability
*Advisory Information*
Title: Sun xVM VirtualBox Privilege Escalation Vulnerability
Advisory ID: CORE-2008-0716
Advisory URL:
http://www.coresecurity.com/content/virtualbox-privilege-escalation-vulnerability
Date published: 2008-08-04
Date of last update: 2008-08-04
Vendors contacted: Sun Microsystems
Release mode: Coordinated release
*Vulnerability Information*
Class: Insufficient input validation
Remotely Exploitable: No
Locally Exploitable: Yes
Bugtraq ID: 30481
CVE Name: CVE-2008-3431
*Vulnerability Description*
Virtualization technologies allow users to run different operating
systems simultaneously on top of the same set of underlying physical
hardware. This provides several benefits to end users and organizations,
including efficiency gains in the use of hardware resources, reduction
of operational costs, dynamic re-allocation of computing resources and
rapid deployment and configuration of software development and testing
environments.
VirtualBox is an open source virtualization technology project
originally developed by Innotek, a software company based in Germany.
In February 2008 Sun Microsystems announced the acquisition of Innotek
[1] and VirtualBox was integrated into Sun's xVM family of
virtualization technologies. In May 2008, Sun Microsystems announced
that the number of downloads of the open source VirtualBox software
package passed the five million mark [2].
When used on a Windows Host Operating System VirtualBox installs a
kernel driver ('VBoxDrv.sys') to control virtualization of guest
Operating Systems.
An input validation vulnerability was discovered within VirtualBox's
'VBoxDrv.sys' driver that could allow an attacker, with local but
un-privileged access to a host where VirtualBox is installed, to execute
arbitrary code within the kernel of the Windows host operating system
and to gain complete control of a vulnerable computer system.
*Vulnerable Packages*
. Sun xVM VirtualBox 1.6.2.
. Sun xVM VirtualBox 1.6.0.
. This issue only occurs in the Microsoft Windows versions of xVM
VirtualBox.
*Non-vulnerable Packages*
. Sun xVM VirtualBox 1.6.4 (for Microsoft Windows)
*Vendor Information, Solutions and Workarounds*
No workarounds exist for this issue. A security bulletin from the vendor
that describes this issue is available here:
http://sunsolve.sun.com/search/document.do?assetkey=1-66-240095-1.
*Credits*
This vulnerability was discovered and researched by Anibal Sacco from
the CORE IMPACT Exploit Writing Team (EWT) at Core Security Technologies.
*Technical Description / Proof of Concept Code*
When the VirtualBox package is installed on a host the 'VBoxDrv.sys'
driver is loaded on the machine. This driver allows any unprivileged
user to open the device '\\.\VBoxDrv' and issue IOCTLs with a buffering
mode of METHOD_NEITHER without any kind of validation. This allows
untrusted user mode code to pass arbitrary kernel addresses as arguments
to the driver.
With specially constructed input, a malicious user can use functionality
within the driver to patch kernel addresses and execute arbitrary code
in kernel mode. When handling IOCTLs a communication method must be
pre-defined between the user-mode application and the driver module. The
selected method will determine how the I/O Manager manipulates memory
buffers used in the communication.
The 'METHOD_NEITHER' is a very dangerous method because the pointer
passed to 'DeviceIoControl' as input or output buffer will be sent
directly to the driver, thus transferring it the responsibility of doing
the proper checks to validate the addresses sent from user mode.
The 'VBoxDrv.sys' driver uses the 'METHOD_NEITHER' communication method
when handling IOCTLs request and does not validate properly the buffer
sent in the Irp object allowing an attacker to write to any memory
address in the kernel-mode.
Let's see the bug on the source. This is the function used to handle the
IOCTL requests at 'SUPDrv-win.cpp'.
/-----------
NTSTATUS _stdcall VBoxDrvNtDeviceControl(PDEVICE_OBJECT pDevObj, PIRP
pIrp)
{
PSUPDRVDEVEXT pDevExt = (PSUPDRVDEVEXT)pDevObj->DeviceExtension;
PIO_STACK_LOCATION pStack = IoGetCurrentIrpStackLocation(pIrp);
PSUPDRVSESSION pSession (PSUPDRVSESSION)pStack->FileObject->FsContext;
/*
* Deal with the two high-speed IOCtl that takes it's arguments from
* the session and iCmd, and only returns a VBox status code.
*/
ULONG ulCmd = pStack->Parameters.DeviceIoControl.IoControlCode;
if ( ulCmd == SUP_IOCTL_FAST_DO_RAW_RUN
(1) || ulCmd == SUP_IOCTL_FAST_DO_HWACC_RUN
|| ulCmd == SUP_IOCTL_FAST_DO_NOP)
{
KIRQL oldIrql;
int rc;
/* Raise the IRQL to DISPATCH_LEVEl to prevent Windows from
rescheduling us to another CPU/core. */
Assert(KeGetCurrentIrql() <= DISPATCH_LEVEL);
KeRaiseIrql(DISPATCH_LEVEL, &oldIrql);
(2) rc = supdrvIOCtlFast(ulCmd, pDevExt, pSession);
KeLowerIrql(oldIrql);
/* Complete the I/O request. */
NTSTATUS rcNt = pIrp->IoStatus.Status = STATUS_SUCCESS;
pIrp->IoStatus.Information = sizeof(rc);
__try
{
(3) *(int *)pIrp->UserBuffer = rc;
}
__except(EXCEPTION_EXECUTE_HANDLER)
{
rcNt = pIrp->IoStatus.Status = GetExceptionCode();
dprintf(("VBoxSupDrvDeviceContorl: Exception Code %#x\n", rcNt));
}
IoCompleteRequest(pIrp, IO_NO_INCREMENT);
return rcNt;
}
return VBoxDrvNtDeviceControlSlow(pDevExt, pSession, pIrp, pStack);
}
- -----------/
At (1), we can see the sentence checking the IOCTL code. The constants
use are defined at 'SUPDrvIOC.h' in this way:
/-----------
#define SUP_IOCTL_FAST_DO_RAW_RUN SUP_CTL_CODE_FAST(64)
/** Fast path IOCtl: VMMR0_DO_HWACC_RUN */
#define SUP_IOCTL_FAST_DO_HWACC_RUN SUP_CTL_CODE_FAST(65)
/** Just a NOP call for profiling the latency of a fast ioctl call to
VMMR0. */
#define SUP_IOCTL_FAST_DO_NOP SUP_CTL_CODE_FAST(66)
- -----------/
With the macro 'SUP_CTL_CODE_FAST()' defined in the same file:
/-----------
#define SUP_CTL_CODE_FAST(Function) CTL_CODE(FILE_DEVICE_UNKNOWN,
(Function)
| SUP_IOCTL_FLAG, METHOD_NEITHER,
FILE_WRITE_ACCESS)
- -----------/
Now we know that the communication method used will be 'METHOD_NEITHER '
(this could also be easily seen by looking at the resulting IOCTL code
in the disassembled binary).
Then at (2) the value returned by 'supdrvIOCtlFast()' is saved in 'rc'
and this is where the problem starts because at (3), the value in 'rc'
is written directly to the buffer pointer sent from usermode without any
check to validate that it is really pointing to an usermode address or
even a valid one.
In this scenario, it is possible to feed the IOCTL with kernel addresses
to write the value returned by 'supdrvIOCtlFast()' ANY address in kernel
space memory as many times as necessary to modify kernel code or kernel
pointers to subsequently get code execution in ring 0 context (that
means, with system privileges).
This is the Proof of Concept I have made to trigger and show the
vulnerability. This will generate a Blue Screen of Death (BSOD) trying
to write to an unpaged kernel mode address (0x80808080) but any other
arbitrary address could be used.
/-----------
// Author: Anibal Sacco (aLS)
// Contact: anibal.sacco@coresecurity.com
// anibal.sacco@gmail.com
// Organization: Core Security Technologies
#include