[windows] How do I execute a *.dll file

I have a DLL file and I want to execute it on Windows. I obtained this DLL file from a challenge site which alleges the DLL should be executed independently.

You can execute a function defined in a DLL file by using the rundll command. You can explore the functions available by using Dependency Walker.

The following series of steps might be helpful:

1. Open Windows Explorer
2. In the top-left corner, click "Organize"
3. select "Folder and Search Options"
4. Switch to the "View" tab
5. Scroll down and uncheck "Hide file extensions for known file types"
6. Click OK
7. Now find the dll file
8. Right-click on it and select "Rename"
9. Change the extension(what comes after the last .) and change it to .exe

DLLs are shared libraries which are used by other windows programs while EXEs are the files which are actually executed and are linked to DLL files so that they can use DLLs.
Both are of same format, PE(portable executable or format of machine code in windows in simple words).
In other words EXEs contain the entry point(main) and the DLLs contain the library functions.. You cannot execute a file which just contains library functions you can just use them via other programs.

But still there are programs like rundll32.exe which provides that entry point and some minimal framework required by DLL functions to be called.
The point that I want to make is, you can never execute a DLL file you can just use it's code by providing an entry point through an EXE or some other program.

It should be mentioned that since it is entirely possible to run DLL's just as any other executable, it has long been considered a security issue. As such, there have been a number of security improvements and registry hacks (sorry no longer have ref-links) that prevents running DLL's from regular user space without extra privileges.

As a good example. I recall making these hacks, but since I no longer remember what exactly I did. I can no longer run any DLLs from normal user shell environment, even though starting various Win apps from GUI works just fine.

That said, one should definitely read "Dynamic-Link Library Security" and "Best Practices to Prevent DLL Hijacking".

To Run a .dll file..First find out what are functions it is exporting..Dll files will excecute the functions specified in the Export Category..To know what function it is Exporting refer "filealyzer" Application..It will show you the export function under "PE EXPORT" Category..Notedown the function name-- Then open the command prompt,Type Rundll32 dllname,functionname (dllname--name of your dll) (Functionname-- name of the function you found under the PE Export) Note:Makesure that your command prompt location is your dll file location

You can't "execute" a DLL. You can execute functions within the DLL, as explained in the other answers. Although .EXE files and .DLL files are essentially identical in terms of format, the distinguishing feature of an .EXE is that it contains a designated "entry point" to go and do the thing the EXE was created to do. DLLs actually have something similar, but the purpose of the "dll main" is just to perform initialization and not fulfill the primary purpose of the DLL; that is for the (presumably) various other functions it contains.

You can execute any of the functions exported by a DLL, assuming you know which one you want to execute; an EXE may contain a whole lot of functions, but one and only one is specially designated to be executed simply by "running" it.

While many people have pointed out that you can't execute dlls directly and should use rundll32.exe to execute exported functions instead, here is a screenshot of an actual dll file running just like an executable:

While you cannot run dll files directly, I suspect it is possible to run them from another process using a WinAPI function CreateProcess:

https://msdn.microsoft.com/en-us/library/windows/desktop/ms682425(v=vs.85).aspx

.DLL files are not executable in the sense that .EXE/.COM/.BAT files are executable, so I'm not sure what you mean.

You can use the Dependency Walker application that comes with the Windows SDK to interrogate a .DLL and see what functions are exported by the file.