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Long-lived Conpherence tabs occasionally cause "invalid CSRF token" errors
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Especially after my laptop goes to sleep (or I close the lid), if I attempt to send a message in a Conpherence tab that I've left open, I'll get an exception about having an invalid CSRF token and a suggestion to clear my cookies. Refreshing the page solves the problem. I also permanently lose whatever message I was composing (probably unavoidable unless we store them client-side).

Event Timeline

I believe that something in this vein is likely the fix:

diff --git a/webroot/rsrc/js/core/behavior-refresh-csrf.js b/webroot/rsrc/js/core/behavior-refresh-csrf.js
index 27c7a9d8ee..b21d2804f3 100644
--- a/webroot/rsrc/js/core/behavior-refresh-csrf.js
+++ b/webroot/rsrc/js/core/behavior-refresh-csrf.js
@@ -48,6 +48,28 @@ JX.behavior('refresh-csrf', function(config) {
   // Refresh the CSRF tokens every 55 minutes.
   setInterval(refresh_csrf, 1000 * 60 * 55);
+  // If the user walks away from their machine for a long time and it goes to
+  // sleep, we may end up in a situation where many hours have elapsed but
+  // the main refresh callback hasn't been invoked. Once a second, check if
+  // we lost some time and refresh immediately if we did.
+  var last_update = null;
+  var detect_sleep = function() {
+    var now = new Date().getTime();
+    if (last_update) {
+      // If it has been more than a minute since the last update, we lost
+      // some time, probably because the machine went to sleep. Fire the
+      // CSRF update event immediately.
+      var delta = (now - last_update);
+      if (delta > (1000 * 60)) {
+        refresh_csrf();
+      }
+    }
+    last_update = now;
+  };
+  setInterval(every_second, 1000);
   // Additionally, add the CSRF token as an HTTP header to every AJAX request.
   JX.Request.listen('open', function(r) {
     var via = JX.$U(window.location).getRelativeURI();

One way to test this would be:

  • Add a "console.log()" or "JX.log()" to refresh_csrf().
  • Close your laptop.
  • Wait a couple minutes.
  • Open it back up.
  • See if refresh_csrf() fires immediately.

I can turn that into a real revision at some point if no one gets there first, but testing it convincingly requires a bunch of sitting around with a closed laptop in different browsers so I'm not going to dive into it right now.

This will also fix the important use case where someone is running their browser inside a VM that they frequently suspend.

We could also rip out all CSRF cycling code completely; Rails uses infinite-duration tokens with no cycling. However, the current code hasn't really caused any issues other than this for a number of years, I believe, and there are some practical-if-obscure attacks this can partially mitigate. An example is:

  • You take a screenshot of a page with the web inspector open to report a bug.
  • You don't notice or censor the CSRF token from the document.
  • With cycling: you're only vulnerable to CSRF attacks for the next 7 hours.
  • Without cycling: you're vulnerable to CSRF attacks for a much longer time / forever.

I have an extra laptop I can use to test this.