Ui issues

[muhammadar323]

Your application doesn't scale the images if the resolution of the 2 devices is different.

[iss4cf0ng]

hi @muhammadar323 ,
Thanks for reporting this. Could you please provide more details about this issue?
It would be helpful to know the exact environment (device, OS, virtual machine?), along with screenshots showing the problem.

[muhammadar323]

I'll send the details when I get home I've left for work now.

[muhammadar323]

IMAGES

win11

win10

Device Information

The c2 server is hosted on win 10 with 720p res screen and the test computer is win11 and has a 1080p screen

Issues in your code

stackoverflow: https://stackoverflow.com/questions/27987085/screen-resolution-not-matching-screen-bounds

based on this i think your issue is in ur DuplexSpy.Payload/winClient48DLL/Form1.cs (lines 2108–2113) where you initialise ur desktop it uses .Bounds which gives scaled value but you want the real pixel values

The below explination is from claude

im not aware about how ur code works etc so i used claude 😅

Hey, here's a full breakdown of the remote desktop resolution bug.

─────────────────────────────
WHAT IS HAPPENING
─────────────────────────────
When a victim machine has Windows display scaling enabled (e.g. 125%, 150% — which is the default on most modern Win 10/11 setups), the remote desktop feature only captures and sends a fraction of the real screen. For example, a 1920x1080 victim machine at 150% scaling only sends a 1280x720 image. The C2 operator ends up seeing an incomplete view of the victim's desktop with the bottom-right portion completely missing.

─────────────────────────────
WHY IT HAPPENS
─────────────────────────────
Windows operates in two separate coordinate systems:

1. Physical pixels — the real pixels that exist on the screen hardware. A 1080p monitor always has 1920x1080 physical pixels regardless of any settings.

2. Logical pixels — a fake, scaled-down coordinate system Windows invented to keep older apps working correctly on high-DPI displays. At 150% scaling, Windows tells apps the screen is 1280x720 and then silently stretches everything they draw to fill the real 1920x1080.

By default, every app runs in the logical pixel world unless it explicitly tells Windows otherwise. This is where the bug comes from.

In Form1.cs, DesktopInit() calls screen.Bounds to measure the victim screen:

var bounds = screen.Bounds;
int width = bounds.Width;   // returns 1280 on a 1080p/150% machine
int height = bounds.Height; // returns 720 on a 1080p/150% machine

screen.Bounds is a C# built-in that queries Windows for the screen size. Because the process has never told Windows it can handle real pixel values, Windows hands back the logical (scaled-down) dimensions. These wrong dimensions are then sent to the server as the "real" resolution.

Then in ScreenShot(), the same problem repeats:

Rectangle capture_rect = Screen.AllScreens[idx].Bounds;
capture_graphics.CopyFromScreen(capture_rect.Left, capture_rect.Top, 0, 0, capture_rect.Size);

CopyFromScreen is the function that actually takes the screenshot. It needs a starting position and a size to know how much of the screen to grab. Both come from screen.Bounds again. So CopyFromScreen starts correctly at the top-left corner but only grabs 1280x720 worth of pixels because that's the size it was given. The remaining portion of the real 1080p screen is never captured at all.

So the bug flows like this:
DesktopInit() measures the screen → gets wrong dimensions from screen.Bounds → sends 1280x720 to server
Server requests a screenshot at 1280x720
ScreenShot() captures using screen.Bounds → same wrong size → grabs only top-left chunk
Server receives and displays an incomplete image

─────────────────────────────
HOW TO FIX IT
─────────────────────────────
The fix is a single Windows API call — SetProcessDPIAware(). This function tells Windows that the process is DPI-aware and can handle real physical pixel values. Once called, Windows stops translating everything into logical coordinates and starts returning true physical dimensions instead. Every subsequent call to screen.Bounds anywhere in the process will then return the correct physical resolution.

Step 1 — Add the P/Invoke declaration to WinAPI.cs:

[DllImport("user32.dll")]
public static extern bool SetProcessDPIAware();

Step 2 — Call it once at the very start of Main(), before anything else runs:

WinAPI.SetProcessDPIAware();

That's the entire fix. No other code needs to change. After this call:
screen.Bounds returns 1920x1080 on a 1080p machine regardless of scaling
DesktopInit() sends the correct dimensions to the server
CopyFromScreen captures the full screen correctly
The server receives and displays the complete 1080p image

Note: the server-side rendering is fine as-is. pictureBox1 is already set to SizeMode.Zoom and Dock.Fill, so it will automatically scale the received 1080p image down to fit the operator's 720p screen with correct aspect ratio. No changes needed on the server side.

[muhammadar323]

Hope this helps

[iss4cf0ng]

Hi @muhammadar323
Thanks! I will check how to resolve this problem.