HTML5 new XSS vectors

So I posted some new XSS vectors on twitter and I thought I’d share them on the blog in case anyone missed them. Safari, Chrome and Opera all support these now :) We have a brand new way of auto executing XSS.

Normally when you find a XSS hole within a input element that has filtered < and > you can’t exploit it automatically without using CSS expressions. The injection looks something like:-

<input type="text" USER_INPUT>

Here you can do style=xss:expression(alert(1)) or moz-binding etc. but it only works on a limited number of browsers. HTML5 however lets us execute like expressions but without css styles. For example:-

<input type="text" AUTOFOCUS onfocus=alert(1)>

We use the “autofocus” feature to focus our element and then the onfocus event to execute our XSS. This works with a plethora (I like that word) of tags. Any form based element it seems you can use this method:-

<input autofocus onfocus=alert(1)>
<select autofocus onfocus=alert(1)>
<textarea autofocus onfocus=alert(1)>
<keygen autofocus onfocus=alert(1)>

5 Responses to “HTML5 new XSS vectors”

  1. Radoslav Stankov writes:

    Really interesting and scary … :)

  2. HtD writes:

    Great Work !

    Its Featured,
    http://hackerthedude.blogspot.com/2009/12/new-html-5-xss-vectors-by-gareth-heyes.html

    Regards,

  3. dalrong writes:

    thank you~

  4. Patrick H. Lauke writes:

    I admit that I don’t quite get what he’s driving at. In most cases, if the user input can contain any characters like spaces, you’d have your server-side script do

    <input type=text value=”[USER INPUT]“>

    as otherwise only the first word before the first space gets taken as a value? Then you’d strip out any double-quotes as well as part of your sanitisation. So in his examples you’d end up with

    <input type=text value=”autofocus onfocus=alert(1)”>

    which I don’t think executes?

  5. Gareth Heyes writes:

    @Patrick

    Well that’s how XSS works, devs forget to filter the quote or others and you can inject your own scripts. BTW spaces aren’t required either for example:-
    <input value=””onfocus=”alert(1)”autofocus/”>