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Re: [caplet] Re: ADsafe and bind

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  • Kris Zyp
    ... If there is an iframe somewhere on the page, they can leak access to it (I was able to reproduce that). Kris ... From: Douglas Crockford To:
    Message 1 of 13 , Sep 8 10:06 AM
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      > I looked at the Mozilla array methods, and wrapped the three that I
      > observed leaking the global object. Under what circumstances do slice,
      > forEach, et al, leak?
      If there is an iframe somewhere on the page, they can leak access to it (I was able to reproduce that).
      Kris
       
       
      ----- Original Message -----
      Sent: Monday, September 08, 2008 11:04 AM
      Subject: [caplet] Re: ADsafe and bind

      --- In caplet@yahoogroups. com, "marcel.laverdet" <marcel@...> wrote:
      > Of course the attack assumes that the host uses Prototype and also
      has an iframe on the
      > page, but I imagine such cases aren't hard to find. There's also
      several other ways you can
      > get window without even depending on Prototype:
      > ([].slice || 0)(0)
      > ([].sort || 0)()
      > ([].forEach || 0)(function( a,b,win){ })
      >
      > So now you're in a tough situation. Do you blacklist all of those
      vectors? I see you're
      > currently using mozilla() to handle concat, reverse, and sort but
      that approach won't work
      > consistently on all sites.

      I looked at the Mozilla array methods, and wrapped the three that I
      observed leaking the global object. Under what circumstances do slice,
      forEach, et al, leak?

    • Douglas Crockford
      ... Thanks, Marcel, that was really helpful. ADsafe s mozilla function is now conditioned on the existence of slots for concat, filter, map, reverse, slice,
      Message 2 of 13 , Sep 8 11:47 AM
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        --- 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?
      • marcel.laverdet
        ... As follows: var leak; ([].forEach || 0)(function(a,b,win) { leak = win; }); leak.alert(leak); Simple demo:
        Message 3 of 13 , Sep 8 11:57 AM
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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 4 of 13 , Sep 8 12:20 PM
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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 5 of 13 , Sep 8 1:06 PM
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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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