javascript - Cross-domain localStorage with iframes (Chrome)

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javascript - Cross-domain localStorage with iframes (Chrome)

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

javascript - Cross-domain localStorage with iframes (Chrome)

I'm trying to store a value on another domain using an iframe (actually, I'm using the xauth library at http://xauth.org/info/). However, when I try to store anything using Chrome, it comes back with "QUOTA_EXCEEDED_ERR: DOM Exception 22", which I've come to recognize as an access error. I've mocked up a couple of very simple pages below to duplicate the effect:

File 1.html:

<html>
<head/>
<iframe src='http://127.0.0.1/2.html' />
</html>

File 2.html:

<html>
<head/>
<script>
console.log(localStorage);
localStorage.setItem('test', '123');
</script>
</html>

If I place both of these on my local server and access localhost/1.html it embeds a frame from 127.0.0.1 (which Chrome considers a separate domain), and I get the same access error as above. At a guess, it looks like even though I'm embedding an iframe from another domain, and the script inside that iframe references the localStorage for that domain properly (as I can see with the console.log(localStorage) line), the permissions for writing to localStorage are coming from the top page's domain.

In short, it looks like no iframe can write to localStorage in Chrome. Does anybody know if there's a way around this particular security "feature"? Or am I doing something wrong?

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1 Answer

深蓝 · Answer 1 · 2021-10-23T21:42:50+0000

The problem only occurs when third-party cookies are disabled. Newer versions of Firefox and Opera are also blocking it. In IE and Edge it is still possible although third-party cookies are disabled. If the localStorage would not be blocked in the iframe, a web tracker could simply include a iframe, read the cookie, send it to the parent script, and then send it to the server.

The reason why this is not blocked in IE and Edge is that these browser allow websites to send third-party cookies, which were previously set as first-party cookies, to the server although third-party cookies are blocked. For example, if a user visits facebook on a regular basis, he gets first-party cookies from facebook. When he then visits other websites with facebook's share button, facebook can track him although third-party cookies are disabled. I really do not know why IE and Edge do not block third-party cookie sending, but I would not use these browsers anyway.

The errors the browsers show when third-party cookies are disabled:

Chrome and Opera: Uncaught DOMException: Failed to read the 'localStorage' property from 'Window': Access is denied for this document.

Firefox: SecurityError: The operation is insecure.

IE and Edge: No error, access to localStorage in iframe is possible although third-party cookies are disabled.

So in conclusion, it is not possible to bypass this security feature (in Chrome, Firefox, Opera) and this is good in order to ensure users' privacy.

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javascript - Cross-domain localStorage with iframes (Chrome)

javascript - Cross-domain localStorage with iframes (Chrome)

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