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Scanning for pointers problem

 
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Pokiaka
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PostPosted: Wed May 16, 2012 4:03 am    Post subject: Scanning for pointers problem Reply with quote

It keeps happening to me so many times, I really need help:

When I'm trying to get a pointer, I get the address, I'm finding out what access the address, and then when the value changes I get the op-codes.
So far it's okay, but then when I try to search the 'easy guess' in hex, I get no results at all.

And it's either my only op-code in the list, or I have more which are irrelevant (something like 0000D352) or repeating the previous pointer I received.
(Sometimes I get the first pointer and it works perfectly, and when I try to get the second one, it gives me the first again).

Example of when I have no results from the op-code:
mov eax,[edi+04]
EAX = 7C9F8380
EDI = 7D1F73BC

Thanks.
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Dark Byte
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PostPosted: Wed May 16, 2012 5:55 am    Post subject: Reply with quote

Quote:

or repeating the previous pointer I received.

that's not possible.
At most the value is the same as the address of the pointer you found (address and value are different things)

Also, remember that the register states are shown AFTER the instruction has been executed.
So in the example code you gave the VALUE at address 7D1F73BC was 7C9F8380

In cases of mov eax,[eax+xxx] you have to remember what the address was that you used "find what accesses" on and then subtract the +xxx from that address to find eax

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Pokiaka
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PostPosted: Wed May 16, 2012 11:09 am    Post subject: Reply with quote

Dark Byte wrote:
Quote:

or repeating the previous pointer I received.

that's not possible.
At most the value is the same as the address of the pointer you found (address and value are different things)

Also, remember that the register states are shown AFTER the instruction has been executed.
So in the example code you gave the VALUE at address 7D1F73BC was 7C9F8380

In cases of mov eax,[eax+xxx] you have to remember what the address was that you used "find what accesses" on and then subtract the +xxx from that address to find eax


You're right, I wasn't accurate. the repeat is same address, with different offset, although still it doesn't work, it lead me to address that goes something like 0000____ with both the offsets on it, and with the last one it lead me to an address that holds the value of 0.
And thanks for the advice, I tried to add the offset, subtracting makes much more sense Razz.

I'll give it a try, but what can I do when there's no offset at all and I still don't get anything from the search? it happened to me here:

mov [ecx],eax
ECX=0C69B1A8
EAX=00000062

Any suggestions?
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Dark Byte
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PostPosted: Wed May 16, 2012 11:22 am    Post subject: Reply with quote

just read it as "mov [ecx+00000000],eax"

Anyhow, look up the instructions above it and see how ecx gets the value. Parhaps the calculation is done earlier

but you really don't find anything when searching for addresses with the value 0c69b1a8 ?

Try scanning for 0c69b1a0, or 0c69b100, or 0c69b000, or 0c698000, or 0c690000 (the heapdata might be useful here)

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Pokiaka
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PostPosted: Wed May 16, 2012 11:48 am    Post subject: Reply with quote

Dark Byte wrote:
look up the instructions above it and see how ecx gets the value. Parhaps the calculation is done earlier

but you really don't find anything when searching for addresses with the value 0c69b1a8 ? (just read it as [ecx+00000000] )


Yes, I get nothing.
You're right that the calculation was done earlier, didn't notice it:

00BAEE49 - mov ecx,[esp+10]
00BAEE4D - mov [ecx],eax
EAX=00000062
ECX=0C69B1A8
ESP=0032A644

But I'm confused about how to proceed.
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Dark Byte
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PostPosted: Wed May 16, 2012 11:59 am    Post subject: Reply with quote

Try a different path, you're not going to find anything useful here (nothing that leads to a static, although if you go far enough, you might get to a decent stable point in the stack)
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Pokiaka
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PostPosted: Wed May 16, 2012 1:08 pm    Post subject: Reply with quote

Dark Byte wrote:
Try a different path, you're not going to find anything useful here (nothing that leads to a static, although if you go far enough, you might get to a decent stable point in the stack)


That's the only op-codes I get.
I tried to mess with the value a lot to see what I can achieve but still nothing.
So what other paths do I have?
And if it's not much to ask, could you explain how is it possible it doesn't work?
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Dark Byte
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PostPosted: Wed May 16, 2012 2:56 pm    Post subject: Reply with quote

Code injection should work

As for why the current path won't find it (have you tried find what access instead of writes? ) is because if the value is stored in the stack you can't make a easy scan for the value as the location will be overwritten often with other random values.
You might be able to track down the origin of that value closer to the base of the stack where it won't change often, but you will need to do single step debugging for that. Which sucks

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Pokiaka
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PostPosted: Wed May 16, 2012 11:38 pm    Post subject: Reply with quote

Dark Byte wrote:
Code injection should work

As for why the current path won't find it (have you tried find what access instead of writes? ) is because if the value is stored in the stack you can't make a easy scan for the value as the location will be overwritten often with other random values.
You might be able to track down the origin of that value closer to the base of the stack where it won't change often, but you will need to do single step debugging for that. Which sucks


Oh I see, sucks indeed. especially that I can't code inject in this case because it probably won't affect only the player, but oh well.
Thank you very much Dark Byte, you've really helped me.
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Dark Byte
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PostPosted: Thu May 17, 2012 5:25 am    Post subject: Reply with quote

If all else fails, try the pointerscan
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Pokiaka
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PostPosted: Thu May 17, 2012 8:23 am    Post subject: Reply with quote

Dark Byte wrote:
If all else fails, try the pointerscan


I did with success. thank you for your help, it's a great tool.
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