[whatwg] <iframe srcdoc> and Content-Security-Policy

Adam Barth w3c at adambarth.com
Mon May 7 11:18:09 PDT 2012 

== Summary ==

When creating a srcdoc document, we need to be careful to avoid
introducing a Content-Security-Policy loophole.

== Details ==

Consider a document with the following Content-Security-Policy:

Content-Security-Policy: default-src 'none'; frame-src *

Now, imagine the following injection vulnerability in index.php:

<body>Hello <?=$username?></body>

This Content-Security-Policy is supposed to prevent the attacker from
being able to inject script into index.php.  However, consider the
following value for $username:

$username = '<iframe
srcdoc="<script>alert(parent.document.cookie);</script>"></iframe>';

In this case, we could get in trouble if the user agent doesn't
enforce the parent document's Content-Security-Policy on the srcdoc
document because the user agent copies the parent document's origin
unto the child document.

== Proposal ==

When creating a srcdoc document, in the same way that we copy the
parent document's origin onto the child document, we should:

1) /enforce/, on the srcdoc document, all CSP policies currently being
enforced on the parent document.
2) /monitor/, on the srcdoc document, all CSP policies currently being
monitored on the parent document.

Please see <http://dvcs.w3.org/hg/content-security-policy/raw-file/tip/csp-specification.dev.html>
for definitions of these terms.

Thanks!
Adam

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