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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.

MS Edge – HTTP Access Control (CORS) Bypass

January 19, 2018

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.

credentials_omit.png

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.

Since fetch was a freshly implemented API, Microsoft’s team might have forgotten about Basic or NTML auth. Whereas with XHR, everything was as per the spec.

Is it exploitable at all?

Yes, given a site has been configured with Basic or NTLM auth and that, in case of cross-domain requests, it responds with Access-Control-Allow-Origin: * (ACAO) which implicitly denies access to responses for authenticated requests. This, in fact, is a very common practice for public API endpoints and is fairly safe against cross-domain data thefts. However, with Edge, anyone could read authenticated resources and steal data which are supposedly private. This, in most circumstances, can also lead to account takeover as attackers can then craft CSRF attacks.

It should be noted that- Using * in ACAO header is really common and poses no risk (except in few circumstances). For example, a quick Censys Search, at that moment, showed 16,216 hosts using “ACAO: *” with Basic or NTLM auth. The number was somewhat similar in Shodan censys_search

These are some platforms/frameworks using HTTP Auth

  • Apache Jackrabbit
  • Microsoft Sharepoint
  • Django Administration
  • Tomcat Administration and many WebDav frameworks

So, essentially, if a website uses Basic or NTML auth and ACAO: *, then an attacker can bypass authentication- allowing him/her access to authenticated resources. This is NOT possible in anyway in other browsers. And, aside from cross-domain reads, it also enables CSRF with custom headers on sites using Basic or NTLM auth in certain circumstances, similar to HackerOne CSRF.

This was patched in early November, 2017 and was also assigned a CVE i.e. CVE-2017-11872, details of which can be found at https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2017-11872.