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Fix iat

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Principle

After finding the program OEP, we need to dump the program and rebuild the IAT. IAT full name is Import Address Table, the entry points to the actual address of the function.

example

For example, as follows, we found OEP and reached the real entry point of the program. We need to dump the program. Right click, select "Use OllyDump to unpack the debugging process" (but you can also useLoadPE`) Dump out):

right_click.jpg

A window pops up to see if the address is correct. The main thing is to check if the 'entry point address' has been selected. Then uncheck the 'Rebuild Input Table'.

dump.png

Name the dump file, I am named dump.exe here. Let's try to run dump.exe, we can find that the program can't run normally. For some simple shells, you dump it and it doesn't work. If you do find the correct OEP and use 'IDAto decompile and see the results well, then your first thought should be that the program 'IAT has a problem. You need to rebuild IAT.

We need to use ImportREC to help fix the input table.

Open ImportREC, select a running process original .exe (original.exe is the process I am debugging in OD, EIP in OD is in OEP position, using OllydumpDo not close this process afterwards.). ImportREC repair input table entry point needs to know OEP, that is, input in the OEP input box in the middle of the right side of the window.

importrec.png

As we know, in Ollydbg we know that the current entry point of the program is 0049C25C, and the mirror base address is 00400000.

So we need to fill in OEP here is 0009C25C

We modify the OEP in ImportREC to 0009C25C and then click on 'AutoSearch`. A pop-up prompt box is displayed, "The discovery may be the original IAT address".

auto_search.png

We can click `Get Imports' button to rebuild IAT. The left side will display the address of each imported function in IAT and whether it is valid. Obviously in the figure you can see ImportREC found in memory IAT Position and detect that each function is valid.

get_imports.png

We click on Fix Dump and open the file that was previously dumped using the OllyDump plugin, which is the dump.exe file.

Then ImportREC will help restore the import table and generate the dump_.exe file. dump_.exe will run normally.


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