Close view-only input, approval-responder and inbound-block gaps in the VNC path

client/vnc/server/server.go

@@ -1039,6 +1039,16 @@ func (s *Server) acquireVirtualSession(conn net.Conn, header *connectionHeader,
 		(*connLog).Warn("session rejected: no username provided")
 		return nil, nil, nil, false
 	}
+	// The requested geometry comes off the wire and is handed straight to the X
+	// server, which allocates a framebuffer for it. The cap the rest of the
+	// pipeline enforces is only checked once the capturer is up, which is too
+	// late to stop a peer asking for 65535x65535. Zero means "use the default".
+	if header.width > maxFramebufferDim || header.height > maxFramebufferDim {
+		rejectConnection(conn, codeMessage(RejectCodeBadRequest,
+			fmt.Sprintf("requested geometry out of range: %dx%d", header.width, header.height)))
+		(*connLog).Warnf("session rejected: requested %dx%d exceeds cap %d", header.width, header.height, maxFramebufferDim)
+		return nil, nil, nil, false
+	}
 	vs, err := s.vmgr.GetOrCreate(header.username, header.width, header.height)
 	if err != nil {
 		rejectConnection(conn, codeMessage(RejectCodeSessionError, fmt.Sprintf("create virtual session: %v", err)))

client/vnc/server/session_clipboard.go

@@ -68,6 +68,12 @@ func (s *session) handleCutText() error {
 	if _, err := io.ReadFull(s.conn, buf); err != nil {
 		return fmt.Errorf("read CutText payload: %w", err)
 	}
+	// Writing the host clipboard changes host state, so a view-only session
+	// must not do it either. The payload is read first regardless, to leave the
+	// stream positioned at the next message.
+	if s.viewOnly {
+		return nil
+	}
 	s.injector.SetClipboard(latin1ToUTF8(buf))
 	return nil
 }
@@ -184,7 +190,7 @@ func (s *session) handleExtClipProvide(flags uint32, payload []byte) {
 		s.log.Debugf("parse ext clipboard provide: %v", err)
 		return
 	}
-	if text != "" {
+	if text != "" && !s.viewOnly {
 		s.injector.SetClipboard(text)
 	}
 }
@@ -254,6 +260,12 @@ func (s *session) handleTypeText() error {
 	if _, err := io.ReadFull(s.conn, buf); err != nil {
 		return fmt.Errorf("read TypeText payload: %w", err)
 	}
+	// Synthesized keystrokes are input like any other, so a view-only session
+	// must not deliver them. The payload is read first regardless, to leave the
+	// stream positioned at the next message.
+	if s.viewOnly {
+		return nil
+	}
 	s.injector.TypeText(string(buf))
 	return nil
 }