Question

Say someone (evil) has set us a timer with setInterval, but we don’t know its ID (we don’t have the reference to the object, that setInterval is returning, nor its value)

(function(){
  setInterval(function(){console.log('pwned')},
              10000)
})();

Is there a way, how to clear it? Is it possible to acces the timer some other way? Or at least in particular browser/javascript engine?

David Flanagan touches similar topic his big JSTDG.
setInterval() method, use in malicious code key in the index points to

… Some browsers detect repeated dialog boxes and long-running scripts and give the user
the option to stop them. But malicious code can use methods such as setInterval() to
load the CPU and can also attack your system by allocating lots of memory. There is
no general way that web browsers can prevent this kind of ham-handed attack. In
practice, this is not a common problem on the Web since no one returns to a site that
engages in this kind of scripting abuse!

Answer 1

From quick test, all major browsers (latest Chrome, Firefox and IE) give pretty small numbers as the ID so just looping “blindly” over all possible numbers should work just fine:

function ClearAllIntervals() {
    for (var i = 1; i < 99999; i++)
        window.clearInterval(i);
}

Full example:

window.onload = function() {
    window.setInterval(function() {
        document.getElementById("Tick").innerHTML += "tick<br />";
    }, 1000);
    window.setInterval(function() {
        document.getElementById("Tack").innerHTML += "tack<br />";
    }, 1000);
};

function ClearAllIntervals() {
    for (var i = 1; i < 99999; i++)
        window.clearInterval(i);
}

#Placeholder div { width: 80px; float: left; }

<button type="button" onclick="ClearAllIntervals();">Clear All</button>
<div id="Placeholder">
    <div id="Tick"></div>
    <div id="Tack"></div>
</div>

This will stop all intervals, can’t stop specific interval without knowing its ID of course.

As you can test for yourself, it should work on all major browsers mentioned above.