OSC 52: Gate clipboard writes on focus to prevent background clipboard hijacking

src/cascadia/TerminalCore/Terminal.cpp

@@ -784,7 +784,12 @@ TerminalInput::OutputType Terminal::SendCharEvent(const wchar_t ch, const WORD s
 // - none
 TerminalInput::OutputType Terminal::FocusChanged(const bool focused)
 {
-    return _getTerminalInput().HandleFocus(focused);
+    if (_isFocused != focused)
+    {
+        _isFocused = focused;
+        return _getTerminalInput().HandleFocus(focused);
+    }
+    return {};
 }
 
 // Method Description:

src/cascadia/TerminalCore/Terminal.hpp

@@ -414,6 +414,7 @@ class Microsoft::Terminal::Core::Terminal final :
     til::CoordType _scrollbackLines = 0;
     bool _detectURLs = false;
     bool _clipboardOperationsAllowed = true;
+    bool _isFocused = false;
 
     til::size _altBufferSize;
     std::optional<til::size> _deferredResize;

src/cascadia/TerminalCore/TerminalApi.cpp

@@ -140,7 +140,8 @@ unsigned int Terminal::GetInputCodePage() const noexcept
 
 void Terminal::CopyToClipboard(wil::zwstring_view content)
 {
-    if (_clipboardOperationsAllowed)
+    // Only allow VT clipboard writes when the terminal has focus
+    if (_clipboardOperationsAllowed && _isFocused)
     {
         _pfnCopyToClipboard(content);
     }

src/host/outputStream.cpp

@@ -282,7 +282,13 @@ unsigned int ConhostInternalGetSet::GetInputCodePage() const
 // - <none>
 void ConhostInternalGetSet::CopyToClipboard(const wil::zwstring_view content)
 {
-    ServiceLocator::LocateGlobals().getConsoleInformation().CopyTextToClipboard(content);
+    auto& gci = ServiceLocator::LocateGlobals().getConsoleInformation();
+
+    // Only allow VT clipboard writes when the console has focus
+    if (WI_IsFlagSet(gci.Flags, CONSOLE_HAS_FOCUS))
+    {
+        gci.CopyTextToClipboard(content);
+    }
 }
 
 // Routine Description: