Inserting data into other processes’ address space, part 1a

I never thought I will write the part 1a of my old post, but here it is.

As usual, I have not explored the below topic in-depth, but have certainly noticed the opportunities and since this is how many interesting developments start, I guess it is still worth … talking…

How do we copy data between processes?

In my old post I have listed a number of inter-process data exchange ideas, but I missed the one that I believe is the most important — at least in 2022 — the non-native stuff. And by that, I mean all these proprietary mechanisms of data exchange that have been developed over the years by vendors different than Microsoft. Many, of course, utilizing the core components of Windows OS, and the very same inter-process communication and cross-process access API functions. Being the ‘genuine’ software and all that, I bet it had to somehow pop up on the radar, and the be filtered out, with time by the likes of AV, EDR, and any other ‘watchmen’… cuz it’s genuine. It’s a stretch, of course, but to their credit, security solutions are getting better and better at detecting any sort of trickery…

With that in mind I started poking around DLLs of known vendors.

I soon discovered a DLL from NVidia (NvIFR.dll) that offers a particular set of exported functions:

  • NvIFR_ConnectToCrossProcessSharedSurfaceEXT
  • NvIFR_CopyFromCrossProcessSharedSurfaceEXT
  • NvIFR_CopyFromSharedSurfaceEXT
  • NvIFR_CopyToCrossProcessSharedSurfaceEXT
  • NvIFR_CopyToSharedSurfaceEXT
  • NvIFR_Create
  • NvIFR_CreateCrossProcessSharedSurfaceEXT
  • NvIFR_CreateEx
  • NvIFR_CreateSharedSurfaceEXT
  • NvIFR_DestroyCrossProcessSharedSurfaceEXT
  • NvIFR_DestroySharedSurfaceEXT
  • NvIFR_GetSDKVersion

hmmm Cross-Process, Shared, and Connect To, and Copy … that certainly sounds interesting!

I don’t have access to any native Nvidia setup, and I don’t play games, so it’s hard to test what these functions really do :(. Quick google for NvIFR_ConnectToCrossProcessSharedSurfaceEXT brought only this interesting reddit conversation.

Poking around the available code, we can speculate that Cross-process Surface interface seems to be accessible via this pipe:


After you write “[\x7F” to it, you can read a buffer of 2136 bytes (in the DLL version I looked at). The buffer we can then read will contain a name of the shared section we can now open, map, and … hopefully write to. The analysis of the code that follows is not straightforward, there are other DLLs being loaded, APIs resolved, and the complexities encountered would really benefit from ‘live’ analysis, but… c’est la vie.

And this is where this blurb ends. I know, I know, it’s not much, but imagine the possibilities. We can find more similar pieces of code, legitimate, genuine software, and cross-process data exchange snippets present inside these signed DLLs or executables… we may as well come up with many new ways of bypassing security solutions that might have not been possible in the past… SHAllocShared

There couldn’t be a less misleading post title than the one I chose for this entry. The function SHAllocShared is documented, may not be very well known, but we may see it more in the future. It is exported by shlwapi.dll and its description has a nice vibe to it:

Allocates a handle in a specified process to a copy of a specified memory block in the calling process.

Hmm… I remember that 15+ years ago or so I was looking at the AppBar functionality. At that time many applications were taking advantage of this desktop feature, so I was really curious how it works. Eventually I created a simple POC that relied on SHAppBarMessage function to add my own app bar, but then got bored and forgot about it.

A few months back I suddenly remembered that POC. I realized that I have never looked at the internals of the SHAppBarMessage function, and with my experiments around code injection via GUI primitives this of course triggered my interest.

Under the hood, the SHAppBarMessage relies on SHAllocShared/SHLockShared and SHUnlockShared/SHFreeShared APIs to create&lock/unlock&free block of memory allocated within program’s address space, and then WM_COPYDATA message is used to send info about the appbar message to ‘Shell_TrayWnd’ window (tray window). Internally, SHAllocShared relies on CreateFileMapping/MapViewOfFile/DuplicateHandle API set to duplicate a handle to existing memory block inside a target process.

This is it. It’s not a lot, but having a set of atomic functions residing inside the shlwapi.dll is probably not a bad thing. This is not as robust as accessibility functions that do a lot of reading and writing of memory blocks between different processes, but it’s always good to have some extra feature at hand.