How to reverse engineer a dll file

As you can see from Screenshot 15, the application is packed using the UPX tool. To unpack it, we are going to use CFF Explorer. After that, we can upload the already unpacked application to IDA Pro and restore the assembler code. We upload our application to IDA Pro once more, and when the system asks us whether to upload symbols from the server, we agree. Here is the result of application analysis in IDA Pro:. You can see in Screenshot 17 that we now have some readable code, more detected functions, and an import table Screenshot At this point, we can run the application and debug it in IDA Pro.

After that, we receive the following warning message:. Our tested application detected that it was debugged. To continue with our analysis, we need to disable debugger detection first. At once, we can notice the NtQueryInformationProcess function.

After clicking on it, we get the following list of xref functions:. The third parameter is an output parameter. After a function call, the result of the function is checked test eax, eax. This value contains the result from al lower bytes. Before that, the esi result is written to eax , and 1 is written to esi. To do so, press N or right-click on the function and select Rename.

Place the cursor over it and click X , or right-click and select Jump to xref to operand :. We already know the first four places where this variable is used, but not the last one. Gladly, this verification can be removed. Press F5 and set the address this way:. Now we can replace this code with, say, jmp to a specific address so that this condition will never be satisfied in real applications, it can be an exception to immediately close the application.

Press F3 and then F2 to switch to the Edit mode. Enter the address of the next command after if. After editing, our modified command is highlighted in yellow. Press F9 to update and save the application. When looking at the assembler code, we see that the new jmp will result in calling esi further down the code, and esi will contain garbage instead of the MessageBox function address.

Thus esi will not be initialized, and the application will crash at Now, we should set the relative address in jmp to 14, but no longer to 1E, because the command has become closer to the command we are going to. Now, to make jmp , we need to save the MessageBox address to esi. In Screenshot 35, you can see that there is an unconditional jump. If we run the application via the debugger, the application will crash because the previous command contains an absolute address, and after the application starts, the loader passes the relocation table and adds delta to each value to make all addresses valid.

What we need to do now is remove this value from the relocation table. Thus, we have to remove the A value from the relocation table. To do so, we need to open the current version of our test application with Relocation Section Editor. CFF Explorer can help us fix this issue.

We have found the value — — on which delta for MessageBox used to be added. You can also add your own functions to API Monitor and use this tool to monitor network function calls and research passed parameters of course, if traffic is not encrypted. So we select only them in User After running our process, we see the list of called functions. Also, we can set different breakpoints for a function:. Read also: Reverse Engineer Software. But before exploring a binary, we need to determine its type with a hex editor.

In our example, we use WinHex. The MZ signature at the zero offset corresponds to PE format files executables or shared libraries , so this is an exe file or dll. Most file formats have unique signatures. Instead, we'll dump its memory and try to run it.

Figure A. Editor's Picks. The best programming languages to learn in Check for Log4j vulnerabilities with this simple-to-use script. TasksBoard is the kanban interface for Google Tasks you've been waiting for. Paging Zefram Cochrane: Humans have figured out how to make a warp bubble. Show Comments.

Hide Comments. Improve this question. Krome Pure. Krome Add a comment. Active Oldest Votes. Improve this answer. I've done this before lost the source of my own project. This is an easy way to get it back. I've just tried it with one of our dll's. Does it work with. It will work with any. NET assembly. Web site static content, such as html files, scripts, images, etc. This didn't work for me.

You must select at least one class in order to form a class diagram. Notice that forming diagram can be a costly operation if you have selected too many classes in forming diagram. All levels in sub diagrams — Show all level residents in the new diagrams multiple single level diagrams. Show as containment relationships Show the containment relationships as connectors in the new diagram.

Notes: The containment relationships between classes are shown as connectors. Presentation Options Option Description Attribute options Show all — Show all attributes of classes in the new diagram. Initial values — Show initial values of attributes of classes in the new diagram.

Operation options Show all — Show all operations of classes in the new diagram. Initial values — Show initial values of operations of classes in the new diagram.

Type options Fully-qualified — Show fully-qualified name of types. Relative — Show name of types relative to this class. Reverse engineer package diagram from source files By reverse engineering package diagram from source files, UML packages and the relationships in between will be produced.