If I access the desktop of a remote Lubuntu 18.04 via vnc or xpra, start a web browser in it, and open some URL to run some web applications in the browser,

  • can any web application tell that I am accessing it from a host different from the host running the browser?

  • can any web application tell when I switch the cursor focus away from the vnc or xpra window or move other applications' windows above to partially hide its window on my local host, while the web browser window is always on top and in focus on the remote host?


  • No , the web applacation only know its own running environment, which is basically the web browser. Even the web browser can't know where does user input come from, it simply know it's from OS, but in reality, no OS would tell a window "Hey, you got mouse movement or key press, remotely!". But some browser like chrome itself provides the remote debugging functionality,in which case itself act as a server, but that's a completely different story. – 炸鱼薯条德里克 Mar 13 at 2:55
  • @炸鱼薯条德里克 please write that up as an answer rather than a comment. – Stephen Kitt Mar 13 at 6:09
  • @炸鱼薯条德里克 Thanks. I heard that some web application can detect that you switch away to a different window from the browser's window? Maybe they request the OS to let them record the desktop of the host where their browser is running? Even if they record the desktop, can any web application tell if I am accessing it from a different host using vnc or xpra? – Tim Mar 13 at 9:18
  • Some browser do provide such info, it's easy to detect wether a window is activated in X window system. If the browser has the ability to do something and expose API to web application, then web app can do it too(require special programming using that API). Notice that, although not natively support, there's some browser support plugin, which increase the ability of browser and web app, e.g., so many Chinese bank website require an ActiveX to fully function. But chrome doesn't support ActiveX because of safety. – 炸鱼薯条德里克 Mar 13 at 10:51
  • @炸鱼薯条德里克 "Some browser do provide such info, it's easy to detect wether a window is activated in X window system", do you mean to detect if a particular tab of a browser is in front and in focus in the desktop environment? If I use VNC or XPRA to access the desktop from another computer (even from the same computer?), keeping the tab of the browser always in front and focus in the desktop in the original computer, while switching between the VNC or XPRA window and other windows on the other computer. I guess no web application can tell that? – Tim Mar 13 at 12:39

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.