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Hunting for a better hex dump tool

January 23, 2017 in, Reversing, Software Releases

Many command line tools are written with an ancient 80×25 terminal size in mind and as such their output is often limited (at least, for a current standard). This is quite amazing that a concept of writing tools destined for such a small terminal is so omnipresent given the fact high resolution computer screens, as well as dual- and multi- monitor setups are now such a common thing.

With this in mind a few years ago I coded a simple hex dump tool which I now use quite often – it gives me a better output than a typical hexdump, and… it was a fun exercise to do. The script is written in perl, fully portable (no dependencies) and… it can for sure be a) buggy b) improved in many ways – use at your own risk ūüôā

The idea that I came with was based on a large amount of unused space I have observed on my terminal (one that I use on Windows). It is typically at least 140×50 and even more, when needed. As such, the 80 columns used by the standard hex dump tool leaves an empty space of at least 70 characters…

Let’s have a look at cygwin’s hexdump ran in a canonical mode:

I had an idea that this gap could be utilized to present more data. So, my script prints the output similar to the canonical output of hexdump, plus a bonus. The bonus includes:

  • the data decimal offset
  • extracted strings (both ANSI and wide) that start within the current line

The output looks like this:

Isn’t that cool?

You can immediately copy many of the strings to clipboard w/o using strings tool.

This is how to run the script:

perl <filename>
perl -s <filename>
perl -S <filename>
-s - extract strings
-S - extract strings, and skip output lines w/o strings

You can download the script here.

If you find any bugs or run into any issue, please let me know.

This is not an EXE, this is not a DLL, This is a Windows App

January 21, 2017 in Reversing

I normally don’t pay much attention to Windows apps, but since I knew calc.exe is just a dumb redirector that loads a Calculator app I eventually got curious and loaded the app into IDA. What caught my eye immediately was a number of exported functions:

  • DllGetActivationFactory
  • DllCanUnloadNow
  • VSDesignerDllMain

When I queried my test win10 system for executables that contain these strings I discovered that pretty much all of them are Windows Apps. I then googled around trying to find out if there is any mention of these functions online, and in particular, how they are being used. I didn’t find anything interesting, but found some references, including this excerpt from an automatically¬† generated build file:

#if (defined(_M_IX86) || defined(_M_AMD64)) && !defined(_VSDESIGNER_DONT_LOAD_AS_DLL)
#if defined(_M_IX86)
#pragma comment(linker, "/EXPORT:DllGetActivationFactory=_DllGetActivationFactory@8,PRIVATE")
#pragma comment(linker, "/EXPORT:DllCanUnloadNow=_DllCanUnloadNow@0,PRIVATE")
#pragma comment(linker, "/EXPORT:VSDesignerDllMain=_VSDesignerDllMain@12,PRIVATE")
#pragma comment(linker, "/INCLUDE:___refMTAThread")
#elif defined(_M_AMD64)
#pragma comment(linker, "/EXPORT:DllGetActivationFactory=DllGetActivationFactory,PRIVATE")
#pragma comment(linker, "/EXPORT:DllCanUnloadNow,PRIVATE")
#pragma comment(linker, "/EXPORT:VSDesignerDllMain,PRIVATE")
#pragma comment(linker, "/INCLUDE:__refMTAThread")

So, looks like the building script depends on the _VSDESIGNER_DONT_LOAD_AS_DLL variable. I installed the latest Visual Studio trial version and queried all files for the ‘VSDesignerDllMain’ and ‘_VSDESIGNER_DONT_LOAD_AS_DLL’ strings… and didn’t get many results either…

Just a few files:

  • Microsoft.VisualStudio.DesignTools.Utility.dll
  • Microsoft.VisualStudio.TestPlatform.BuildTasks.dll
  • Microsoft.Windows.UI.Xaml.81.Build.Tasks.dll
  • Microsoft.Windows.UI.Xaml.Build.Tasks.dll

Their code didn’t really explain much (none of them actually refer to code using the ‘VSDesignerDllMain’ function, only generate files containing references to it).

So, I am curious what is the purpose of these functions… either some legacy tool, or some internal testing platform? ‘VSDesigner’ suggests IDE integration of some sort – potentially quicker way to debug the app? Anyway, just guessing here…¬† If you are a Windows App programmer, or spent more time on reversing Apps and know how these are being used I’d be grateful if you could share.

In terms of code, the function simply calls the _DllMainCRTStartup function after setting the internal variable VSDesignerDllMain_status to 3, the DllMainCRTStartup eventually calls DllMain function:

So, we have 2 entry points – one for the Windows exe (‘start’) and the second one for the DLL (‘VSDesignerDllMain’->’DllMain’)

In the mean time, a typical Windows App is like a Frankenstein’s monster – it is a MZ DOS executable, a PE executable & DLL in one, a .NET assembly, a HTML/XAML madness, and… it can’t be even launched directly from the Explorer, because it needs to be activated via one of the 3 methods offered by the IApplicationActivationManager COM interface (AFAIK, not sure if there is any other way). While the plot thickens the platform gets more and more complicated and reversing work harder and harder…