full-disclosure - Exploiting heap overflows in W2K

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Date: Tue, 1 Aug 2006 07:46:23 +1200 (NZST)
From: Ivan Stroks <ivanstroks@...oo.co.nz>
To: full-disclosure@...ts.grok.org.uk
Subject: Exploiting heap overflows in W2K

Hi list,
 
  I am trying to exploit a Heap buffer overflow vulnerability and facing some problems, hope you could help.
  I run the vulnerable program in a VMWare, attached with Olly.
 
  These are my problems:
 
  1. I control both EAX and ESI, when the program goes to 
 
     mov [esi], eax
     mov [eax + 4], esi
 
     First of all, I tried gainig control of execution through PEB but, according to Halvar's presentation, there are some restrictions to what you can write in the header of the overflowed buffer.
     Quoting: 
     
     " Properties our block must have:
 
         Bit 0 of Flags must be set
         Bit 3 of Flags must be set
         Field_4 must be smaller than 0x40
         The first field (own size) must be larger than 0x80
 
         The block XXXX99XX meets all  requirements"
 
     So, supposing PEB pointer to overwrite is 0x7FFDF020 I would need to specify for example: XXXX20f0fd7f, but this is not matching required properties and so RtlFreeHeap exits.
     I am sure I must be missing something here, but can't find it.
 
  2. An aditional problem I am facing, due to the fact that this is my first heap overflowing session, is that when I trigger the vulnerability as soon as the programs comes back from "revert snapshot" then I get to rtlHeapFree ok, but if some other request are performed to the program before, then I cannot reproduce that behaviour again and different behaviours and situation arise.
    It is obvious that my exploit won't be the first request the program receives so, how can I manage this?
 
 
    Hope you could help!
    Regards
 
 IvaN!
 
 
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