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Exploiting POST-based XSSI

We know, more and more client-side attacks are dying. But sometimes, with introduction of new features, an unexploitable becomes exploitable. Yes, combined with the power of Service Worker, XSSI is no longer limited to GET requests. This essentially means we can also include resources with POST requests and CORS-safelisted headers. The idea is simple- intercept the request and modify to send no-cors POST request. For demonstration purpose, I’ve built a rough POC at https://cm2.

XSS with length restriction

There are situations where you can execute JavaScript but you’re limited to alert because it only allows limited number of characters. I recently saw a report on HackerOne with exact same situation- which is why I’m writing this post. The reporter managed to execute arbitrary JavaScript but made it somewhat complicated and required few user interactions. This drastically lessens the severity and no doubt, results in small reward. The more promising Proof of Concept in case of XSS, in my opinion, is to load external JavaScript from a domain under your control.

On-site Request Forgery

You might have heard of Server Side Request Forgery or SSRF, and probably already came across On-site request Forgery. Let’s call it OSRF for brevity and not to confuse with CSRF. This post aims to briefly explain what OSRF is and how it differs from SSRF, possible impacts and remedy. To begin with, SSRF is a type of vulnerability where an attacker is able to influence Servers to send crafted requests to their destined location.

Forging Content-Type Header With Flash

You might already know how you can forge HTTP request headers using flash. So, to keep it short, I’m talking about Content-Type only. Lately, I’ve been seeing tweets & reports about CSRF attack involving JSON data. In fact, I saw a tweet asking if it was safe to rely on Content-Type: application/json for CSRF protection. And, going through the replies, I found it was concluded safe- because browsers don’t yet support application/json in HTML form submission.

HackerOne XSSI – Stealing Multi Line Strings

I assume you already know what XSSI is. If not, here’s a brief introduction cited from Identifier based XSSI attacks Cross Site Script Inclusion (XSSI) is an attack technique (or a vulnerability) that enables attackers to steal data of certain types across origin boundaries, by including target data using SCRIPT tag in an attackerss Web page as below <!-- attacker's page loads external data with SCRIPT tag --> <SCRIPT src="http://target.

MS Edge – HTTP Access Control (CORS) Bypass

This is a short post about a vulnerability I had found in Microsoft Edge. TL;DR Edge failed to recognize HTTP Authentication information (i.e. Authorization Header) as credential information when sending fetch requests. So, if an application uses Basic or NTLM auth, Edge would send Authorization header in all fetch requests despite specifying not to include credentials. If you noticed, I explicitly specified not to include credentials. Yet, it was sent despite me specifying not to and you can see the response in console.
Referrer Policy

Referrer Policy

There are, atm, 5 different ways referrer policy can be delivered as defined by W3C. Setting referrer policy via meta is supported by all modern browsers (as shown above). The other ones, however, are new and aren’t widely supported or used. The HTML Standard defines the concept of referrerpolicy attributes which applies to several of its elements, for example: <a href="http://example.com" referrerpolicy="origin"> In general, the order in which these signals are processed are

Stealing CSVs Cross-domain

Back in 2008, Chris Evans found it was possible to steal data cross-domain in Firefox using script includes. We can still read his report at http://scary.beasts.org/security/CESA-2008-011.html In his own words: The modern web model permits remote domain <script> inclusion with no restrictions. If the remote data, which does not have to be script, has an effect on the evil domain doing the inclusion, you have a cross-domain data leak.

Referrer Policy

January 19, 2018

Referrer Policy

There are, atm, 5 different ways referrer policy can be delivered as defined by W3C. Setting referrer policy via meta is supported by all modern browsers (as shown above). The other ones, however, are new and aren’t widely supported or used.

The HTML Standard defines the concept of referrerpolicy attributes which applies to several of its elements, for example:

<a href="http://example.com" referrerpolicy="origin">

In general, the order in which these signals are processed are

The referrerpolicy attribute allows overriding referrer policy defined earlier via meta tag or Referrer-Policy header. There’s another widely used attribute to control referrer as well i.e rel=“noreferrer”. Though widely used, it doesn’t provide much control over what referrer to be sent. It merely instructs browsers not to send referrer at all, and it has highest preferences over other referrer policies. I created a page for checking referrer policies which you can access at http://cm2.pw/referrer/

There, I’ve also added ’noopener’ and ’noreferrer’. Passing policy value via ?policy sets referrer policy via meta tag.

Testing different browsers, my observations are as follows: Only Chrome and Opera has support for ‘noopener’ (Firefox 52 for Developers has started implementing it). However, MSIE & MS Edge both don’t seem to support any- setting window.opener in all cases. On the other hand, ‘noreferrer’ also sets window.opener to null in browsers supporting it. Therefore, beside using ’noopener’ and ’noreferrer’, it’s best to set window.opener to null manually. relnoopener

The HTML5 standard added support for the attribute/value rel=“noreferrer”, which instructs the user agent to not send a referrer.

Currently, only Firefox (50+), Chrome (46.0+) and Opera(42.0+) support referrerpolicy attribute. Setting referrer policy via meta tag is supported in all major browsers, but beside these 3, other browsers are still following older one with values ’never’, ‘always’, ‘origin’ and ‘default’.

Conclusion

Improper referrer policy leads to leakage of referrer information, which may contain sensitive data as well. For example, Java applications may leak session token in URL. In such cases, if an attacker is able to post his own link, improper referrer policy may give him full access to victim’s account.

The default behavior is to send the origin as referrer to a-priori as-much-secure destination (https->https) and not to send any referrer to a less secure destination (https->http). The best option, imo, is to use origin-when-crossorigin which sends full URL when performing a same-origin request, but only send the origin of the document for other cases.

The rel="noopener noreferrer" adds an extra layer of protection. Normally, opening a new browsing context, tab or window or frame, gives child window a reference to its parent window via window.opener property. And setting its location property, a user can redirect parent window to any location unless explicitly disallowed. This gives an attacker the ability to navigate users’ trusted browsing contexts to any location of his/her choice, read more at https://mathiasbynens.github.io/rel-noopener/.

Image Sources

http://caniuse.com/#feat=referrer-policy http://caniuse.com/#feat=rel-noopener