Microsoft Excel Could Allow Remote Code Execution by Malformed FNGROUPCOUNT
value Vulnerability

By OYXin( xin.ouyang at google mail ) of Nevis Labs
http://www.nevisnetworks.com

Vendor
Microsoft Inc.

Products affected:
Microsoft Office 2000 Service Pack 3
Microsoft Office XP Service Pack 3
Microsoft Office 2003 Service Pack 1 or Service Pack 2
Microsoft Works Suites
Microsoft Office X for Mac
Microsoft Office 2004 for Mac

Overview:
A remote code execution vulnerability exists in Excel using a FNGROUPCOUNT
value. An attacker could exploit the vulnerability by constructing a
specially crafted Excel file that could allow remote code execution.

Details:
The vulnerable code is similar to MS06-012(CVE-2006-0031) which found by
eyas.

==============================================================================
eax=0e0e0e0e ebx=0000fff1 ecx=00002241 edx=0000000f esi=00138964
edi=0013ffff
eip=30093040 esp=0013794c ebp=001388e4 iopl=0 nv up ei pl nz na
po nc
cs=001b ss=0023 ds=0023 es=0023 fs=003b gs=0000
efl=00010206
*** ERROR: Symbol file could not be found. Defaulted to export
symbols for Excel.EXE -
Excel!Ordinal41+0x93040:
30093040 f3ab rep stosd
es:0013ffff=74634100

Excel!Ordinal41+0x9302e:
3009302e 5c pop esp
3009302f f3ffff rep ???
30093032 8bd9 mov ebx,ecx
30093034 c1e902 shr ecx,0x2
30093037 8d7c1520 lea edi,[ebp+edx+0x20]
3009303b b80e0e0e0e mov eax,0xe0e0e0e
30093040 f3ab rep stosd

> 0:000> g
> (b98.5fc): Access violation - code c0000005 (first chance) First
> chance exceptions are reported before any exception handling.
> This exception may be expected and handled.
> eax=00000000 ebx=00000000 ecx=0e0e0e0e edx=7c9037d8 esi=00000000
> edi=00000000
> eip=0e0e0e0e esp=0013757c ebp=0013759c iopl=0 nv up ei pl zr na
> po nc
> cs=001b ss=0023 ds=0023 es=0023 fs=003b gs=0000
> efl=00010246
> 0e0e0e0e ?? ???

POC:
No POC will be supplied

Fix:
Microsoft has released an update for Microsoft Office which isset to address
this issue. This can be downloaded from:
http://www.microsoft.com/technet/security/bulletin/MS06-037.mspx

Vendor Response:
2006.04.12 Vendor notified via [email protected]
2006.04.12 Vendor responded
2006.07.11 Vendor released MS06-037 patch
2006.07.12 Advisory released

Reference:

1. http://sc.openoffice.org/excelfileformat.pdf
2. http://www.microsoft.com/technet/security/bulletin/MS06-037.mspx
3. http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2006-1308
4. http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2006-0031

Greetings to Nevis lab guys and 0x557 guys :)