On 19-Oct-09, at 5:39 PM, Adam Barth wrote:
On Mon, Oct 19, 2009 at 6:43 AM, Johnathan Nightingale
Not as limited as you might like. Remember that even apparently
non-dangerous constructs (e.g. background-image, the :visited
can give people power to do surprising things (e.g. internal
sweeping, user history enumeration respectively).
I'm not arguing for or against providing the ability to
block-inline-css, but keep in mind that an attacker can do all those
things as soon as you visit attacker.com.
Yeah, I think you're absolutely right that CSP is primarily about
preventing attackers from exploiting your browser's trust relationship
with victim.com, and the examples I offered are (for lack of a better
term), victim-agnostic. They don't steal victim.com credentials or
cause unwanted changes to, or transactions with, your victim.com
I do think, though, that a helpful secondary effect of CSP is that it
reduces attackers' ability to amplify the effect of their attacks.
You're right that it doesn't take much to get users to click on a
link, but I think it is nevertheless the case that a good history
enumerator or ping sweep which happens in the background while you're
reading a NYTimes article will have a substantially higher success
rate than a link in the comment section that says "Click here for free
goodies." Basically by definition, link-clickers are a subset of your
total prospective victim pool.
I think this is more specifically what makes me feel like there's
still value to locking down all inline styling, or at least providing
that facility, but I appreciate you forcing me to refine my thinking a
In the past, I've found it helpful to simply assume the
user is always visiting attacker.com in some background tab. After
all, Firefox is supposed to let you view untrusted web sites securely.
Yes, absolutely so. We should continue to try to bend smarts towards
fixing :visited and other nasty sleights-of-hand. But the one course
of work doesn't preclude the other (and I don't think you were saying
that it did).
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