Вы можете попробовать вот так:
В поле зрения.
filebrowserImageUploadUrl: '../../Upload/uploadnow'
В контроллере
public ActionResult uploadnow(HttpPostedFileWrapper upload, string CKEditorFuncNum)
{
string path = "";
string pathWeb ="";
if (upload != null)
{
string ImageName = upload.FileName;
string extention = Path.GetExtension(ImageName);
string name = DateTime.Now.ToString("yyMMddhhmmssms");
ImageName = name + extention;
pathWeb = "/images/uploads/" + ImageName;
path = System.IO.Path.Combine(Server.MapPath("~/images/uploads"), ImageName);
upload.SaveAs(path);
HttpContext.Response.Write("<script>window.parent.CKEDITOR.tools.callFunction(" + CKEditorFuncNum + ", \"" + pathWeb + "\");</script>");
HttpContext.Response.End();
}
return View();
}