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Windows Metafile SetPalette Entries Heap Overflow (MS05-053)
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SUMMARY
Windows Metafile (WMF) is a common graphics file format on Microsoft
Windows systems. It is a vector graphics format which also allows the
inclusion of raster graphics. Essentially, a WMF file stores a list of
commands that have to be issued to the Windows graphics layer GDI in order
to restore the image. WMF is a 16-bit format introduced in Microsoft
Windows 3; a newer 32-bit version with additional commands is called
Enhanced Metafile (EMF). EMF is also used as a graphics language for
printer drivers.
A vulnerability has been discovered in the way the Windows Graphical
Device Interface (GDI) processes Windows Metafile (WMF) format image files
that would allow arbitrary code execution as a user who attempts to view a
malicious image. An attacker could send such a metafile to a victim of his
choice over any of a variety of attack vectors, including an HTML e-mail,
a link to a web page, a metafile-bearing Microsoft Office document, or a
chat message.
DETAILS
The code in GDI32.DLL responsible for rendering Windows Metafiles contains
an integer overflow vulnerability in the function PlayMetaFileRecord,
cases 36h and 37h, which handle "SetPaletteEntries"-type records. If the
reported length of such a record is 7FFFFFFFh or FFFFFFFFh, the following
code will experience an integer overflow and can be made to allocate an
insufficient heap block, the success of which incorrectly implies the
validity of the length:
77F5BC38 mov eax, [ebx] ; length field
77F5BC3A lea eax, [eax+eax+2] ; *** integer overflow ***
77F5BC3E push eax
77F5BC3F push edi
77F5BC40 call ds:LocalAlloc
...
77F5BC51 mov ecx, [ebx] ; length field
77F5BC53 add eax, 2
77F5BC56 shl ecx, 1 ; copy size != allocation size
77F5BC58 mov edx, ecx ; intrinsic memcpy() follows
77F5BC5A mov esi, ebx
77F5BC5C mov edi, eax
77F5BC5E shr ecx, 2
77F5BC61 rep movsd
77F5BC63 mov ecx, edx
77F5BC65 and ecx, 3
...
77F5BC6D rep movsb
Although the copy length is similarly subject to an integer overflow, the
two differ by a "+2" term, and therefore the allocation size can be made
very small while keeping the copy length extremely large. The result is a
complete heap overwrite with arbitrary binary data from the metafile.
Vendor Status:
Microsoft has released a patch for this vulnerability. The patch is
available at:
<http://www.microsoft.com/technet/security/bulletin/MS05-053.mspx>
http://www.microsoft.com/technet/security/bulletin/MS05-053.mspx
Related Links:
This vulnerability has been assigned the following IDs:
<http://eeye.com/html/research/advisories/AD20051108a.html>
EEYEB-20050901
OSVDB ID: <http://www.osvdb.org/displayvuln.php?osvdb_id=20579> 20579
CVE ID: <http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2005-2123>
CAN-2005-2123
ADDITIONAL INFORMATION
The information has been provided by eEye.
The original article can be found at:
<http://eeye.com/html/research/advisories/AD20051108a.htm>
http://eeye.com/html/research/advisories/AD20051108a.htm
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