Unfortunately we’re never quite safe and this lecture from DEF CON 24 is well worth watching. If you think your VPN or HTTPS connection is protecting that important internet connection then you might think again after viewing this!
Transcript from Video:
>> Morning, Alex Chapman, this is Paul Stone and this is our talk: Toxic Proxies – Bypassing HTTPS and VPNs to Pwn Your Online Identity. So first off, thank for you coming here on a Sunday afternoon. Uh, really good to see so many people turning out for this, so… uh, thank you very much and we’ll get started. So, okay, first we’re gonna start with a demo, in the video streaming this works. So, this is what we’re, uh, this is an example of this thing we’re gonna be talking to, about today. And this is actually being, about being able to extract information from HTTPS streams on a local network, uhm, you’ll see some of the information there so, instead of just a boring slide it’s really just a quick demo of the sort of thing that we’re gonna be showing you. So as I said my name’s Alex and my colleague Paul Stone. We both work for Context Information Security in the UK, uh, I’m on.. Ooops! On twitter and PPJ Stone standing next to me.
Uhm, I’ll explain that demo in a little bit more detail as we go through. >> So, this is our talk, the exciting introduction which you just saw, I hope everyone else found it as exciting as I did. Uhm, we’re gonna start with some history. This is the 1 0 1 track, we’re gonna talk a little bit about the problems faced, what’s been going on, uh, how we got to where we are today. And, how are, the attack that we’re gonna describe kinda fits into all of that. We’re going to explain the attack, we’re gonna show how you can, uh, sniff data from a HTTPS streams, we’re gonna steal that data, we’re gonna actually do something with it and then we’re gonna show how it can ultimately be used to kind of steal your, your online accounts. Uh, we’re then gonna talk a little bit about VPNs and how we’re against this or not against this. Uh, and then put in place some real mitigations about what we should be doing on, uh, on these systems to, to help make them more secure.
And then we’ll talk, uh, a little bit about the, the fixes that have been put in place by various fenders around these issues. So… Where are we starting? This is a, uhm, this is a kind of attack that we’re looking at from a rogue access point perspective. So rogue access points have reasonably, uh, privileged access to a network anyway. You, you control the DNS, DHCP and all the rest of it so you can, you already in a system where you can kinda monitor and insert data.
Uh, it’s… so, good? so, back in the 1993, no, no encryption, right? So, we’re, we’re here on a Mosaic browser, browsing away, everyone can see everything that’s going on. And then somebody came and thought “Well, what if I want to do something sensitive over this?” So… we headed off to encryption. We’re talking SSL here, so Netscape, uhm, to shift with SSL in 1995, so again, a good 20 years ago. Uhm, users were somewhat safe from passive sniffing attacks, we obviously know nowadays that the SSL back then was awful and terribly terribly broken, but, at the time it was what we needed it to be.
But, SSL wasn’t perfect so a lot of websites can’t seem to, over both HTTPS and, uh, sorry and HTTP and HTTPS and, uhm, people connect of HTTP first – cause who, who writes in the “S” when putting their URLs? Who even puts in the screener? Uh, and evil, uh, men and invented such to prevent users from reaching HTS, HTTPS sites and having to fall back to the unencrypted sites. So, it wasn’t great and Moxie Marlinspike, uh, demonstrated this in 2009 with SSL strip, great, for, for the time… For man meddling, uhm, these connections damn better than the multiple HTTP and these was the sort of padlock in the corner of the screen wasn’t there. Uh, and again a lot of users wouldn’t be checking that anyway.
Uhm, script sample of… that’s the shell script for those, uh, who haven’t seen it before – browse to an HTTP site, uh, what it’s supposed to do is redirect to the HTTPS through to the redirect, uhm, that’s shell script in the middle of that. We’ll actually stop the redirect from happening. So, if shell script broke HT, uh, HTTPS connections by simply ignoring them and straighten them out with the string. Uh, and browse members obviously had to do something about this to make those connections, and, uh, uh to match various websites with more secure. So this is where we introduced, uh, introduced HTTP strip transport security. Uhm and this is somewhere around 2010, so again, a good 6 years ago. That, that picks up by a lot of major websites, uh, big news article came out; Google dot com going full, going HTTPS, uhm, so it’s taking a while but it, but it is getting there. Uhm, and, HTTPS essentially prevents browsers from requesting the plain text HTTP resource in the first place. So, we don’t have the option of doing the SSL strip. That’s …
Kind of where we are in the present day. HTTPS is doing a pretty good job. So nearly all traffic to sites we use on a daily basis, uhm, is encrypted with HT, HTTPS and HSTS protected so theoretically we’re now, we’re in a coffee shop, in the pub, on our laptops we should be fine. Right? We need a new style of attacks and this is something we came across about 6 months ago now and show the attack too… show you how it can be used and, uh, the work that we’ve been able to do with it. So hand over to Paul to, uh, share some information. >> Okay! Uh, hello. So, uhm, Alex has given you a bit of history, uhm, and I’m gonna give you a little, a little bit more history. So bear with us until we get to the fun, new stuff. Uhm, so just to introduce PAC files for people who haven’t heard about them before. Uhm, so, a, uh, PAC files exist because, uh, large companies have very complex internal networks; lots of different proxies, and they need some way to be able to figure out which proxy to connect to depending on the site you, you want to visit.
Uhm, and they’re various other things as well so , uh, DNS, uhm, lookups with, uh, will lose the, uh, uh, DN suffix and look the like WPAD dot internal dot company or whatever. Uh, and there’s also, uhm, NETBIOS, LLMNR and all of that as well. So there are lots of way that WPAD can work. So the WPAD attacks are very well known, uhm, they’re, uh, a whole bunch of tools that will make it very simple to inject, uh, or spoof WPAD responses, uhm, and if you can do that you can then target, uh, one machine or a whole bunch of machines and hijack all that traffic and root, root their traffic, uh, their web traffic through their malicious proxy.
So that means that all plaintext, uh, non-HTTPS traffic can be modified or viewed by the attacker. Uhm, so, this is a bit, a bit, we quite enjoy reading the WPADs it can be set minimally, it can be set at the WPAD protocol does not create any new executing weaknesses – kind of famous last words there. Uhm, did you want to…? >> Oh, yea, yes. >> So, yea, just really quick, uhm, overview of how this thing get, uh, pushed out, so, a laptop or network ask router for, uh, HTTPS options through to the, can correspond to the option 2 5 2, uhm, which is the URL to, uh, a PAC file which the system then go download and use as it’s PAC file chooses the proxies to get to the internet. Alternatively the, uh, if , if it doesn’t receive, a, a PAC file through that it’ll do a DNS lookup for WPAD dot search domain – so the search domain that was, uhm, either preconfigured or was pushed out of the HSTS.
If the router, uh, responds to that it can then respond with the IP of the mal, of the host which can serve, uhm, a PAC file and in this case will also be serving malicious PAC files. Uhm, the last method is from uh a network with a malicious activist on the network not actually on the router. So if the system still haven’t got a, uhm, a PAC file it’ll send out a Link Local Multicast Name Resolution request for WPAD.
So if you ever washed up on a Windows network you’ll see loads of request for things like WPAD, uhm, just being broadcast to other systems on network. If any other system on that network responds that system, sorry, the the user’s system will use that response, uhm, uh, to go and grab the, uh, PAC file from from the IP address given there.
I think that got to… So, uhm, Windows has had WPAD turned on by default, uhm, and this is even in Home edition so this is a very, kind of, corporate thing. There’s no reason to have this on your home network but it’s still in Windows 10 enabled by default. Uhm, local network attackers can, can exploit this and there are tools that Paul shared a link to earlier. But, fortunately again, with these HTTP, HTTPS and HSTS traffic there’s theoretically at this point nothing the attacker could be able to do our connections to, uh, kind of get our data. And that’s what we’re gonna, gonna show you next. So, throughout this research, uhm, we also follow the trend of naming our vulnerabilities and we, we’ve got a few, kind of projected titles and this was one of my favourites: “breaking WPAD”. Uhm, Paul actually did the, uhm, did the posters and I think probably spent more time on that than his actual talk… But, uhm..
Hang back… >> Okay, uh, a little bit theory before we get to the really fun stuff. Uhm, so what does a PAC attack look like? So a typical PAC script might look like this… So the idea is that there’s three different proxies and depending on, uhm, uh, what your, the host name ends in or routes, uh, the browser to one of the proxies. So every PAC script has to define this function, this exact name called “find proxy for URL” and it takes two parameters, uh, the full URL and the host name. So most, uh, most PAC scripts will look at a host and make a decision based on, on a suffix and say use this, use this proxy or this proxy.
Very simple. So, like I said, there’s this one function called “find proxy for URL” and, and according to the spec it takes full URL and the host name as parameters and returns the string. And in this case it returns direct which means don’t use any proxy. Uhm, so… It’s the full URL that gets passed into this, uh, PAC scripts which is potentially a malicious PAC script.
Can anyone see the problem yet? So the full HTTPS URL is now known by this attack- uh attackers piece of code and its potentially malic- malicious. h So what can we do with that and why is that kind of bad? So java scripts in the PAC file isnt like java script in the website you dont have the full range of functions to uh put stuff on the screen and talk to the dom and all that kind of stuff. These are the functions uh this is essentially the API uh that PAC scripts have access to and the two that really stand out to us is DNSresolve and isresolvable so DNS resolve as you might expect takes the host name and returns an API address and isresolvable takes a host name and returns true or false so these are interesting because they let the PAC scripts talk to the outside world so we have sensitive data going in and we now have a way to communicate with the outside world.
So putting it altogether here is our very simple malicious PAC script uh and what it does is it takes the uh takes the URL checks if its uh HTTPS and therefor potentially sensitive um it then uh uh appends dot leak onto the end so in this case dot leak is uh a domain thats controlled by the attacker and then it replaces all the special characters with this uh dot.
Uh so uh for example we have a sensitive URL there with a with a nice authtoken in and this the scripts will uh convert it into the string and then um uh do a DNS look up and the attacker receives this uh sensitive token but to the um back to their DNS server so thats the attack. Uh and of course um if you cant fit it in a tweet then its not a real vulnerability and it fits uh very nicely into a tweet there. Uh so going back to the uh variable attack the malicious gateway so um as we said before uh malicious gateway can uh can incept any plain text HTTP traffic easy but if were talking HTTPs then uh this hacker cant incept that HTTPS traffic. But if we now are leaking every single HTTPS url uh so the uh malicious gateway uh tells your laptop to use a malicious PAC script and now its leaking at all the HTTPS URLs um and then the https traffic is going to the server so you can sniff HTTPs URLs and modify the plain sec- plain text HTTPs traffic.
So just to kind of uh sum this up in a nutshell. Um PAC files allow attacker controlled java script to see every single HTTPS URL before it gets requested by the browser the PAC file can then leak that data to an attacker by DNS so the whole point of HTTPS is to protect uh sensitive data on untrusted networks but with a WPAD and Pac uh an attacker essentially can do an end-run around HTTPs. Uh this is the second title we have but this is my favorite one APACalypse now uh Im quite pleased with that one. Okay so demo time. >>Right you might have to bare with us on this we uh we didnt realize we wouldnt have any ethernet connection up here so were acutally trying to do these demos live through uh the wifi on my phone, well see if it works >>If it works there will be a miracle okay so the set up we have is on the right we have a a VM which is the the victim and on the left we have our, uh, attacker with a, a fancy, uh, control panel.
So I’m gonna open up Chrome. So at this point the malicious gateway has already sent the message PAC file and you can see at the bottom here we’re already getting tons of URLs being leaked, uh, by, by Chrome. So, uh, I am now going to search for something. So, uh, everything you do on Google goes to direct GPS as you can see, as I was, as I was type, as I was searching, as I was typing it’s being leaked to the attacker and appearing on their side. Uhm, and now I can browse to Wikipedia which is HTTPS, uhm, I can just browse around Wikipedia. And, uh,the, tire’s load, you get so much, so much traffic here at the bottom with all the URLs being leaked, uh, and at the top they’re kind of pulling out the interesting stuff.
Not the pages that you are actually visiting. That’s that… I can search for something else. So again, DefCon site is HTTPS, uhm, yea. So… there we go, yea. So that’s what we can do, literally just be leaking, a, leaking everything. And… Thank you! Uhm, so, yeah, most websites these days are HTTPS and, uh, we can see that stuff now with this attack which is quite nice. Right, I’mmm now gonna hand over toooo, uh, no! Not yet.
>> You can keep going. >> Okay, so, passively, uh, seeing this data as the user browses is quite nice, but, were impatient. As an attacker they may be connected to our malicious hotspot only for a short amount of time. So, the challenge we set ourselves was to actively steal as much data as possible. Using only URLs. Now remember, this attack doesn’t let us completely vacate the GPS, we can’t see everything, uhm, we can only see the URLs including the path networking string. We don’t get any, uh, post data, we don’t get any cookies, any headers, we don’t get the responses, uh, uh, response bodies. Uhm, so we have this, uh, kind of superpower but it’s a really limited super power. Uhm, but, yea… limitation is good, let’s just be creative. Uh, and, one of the key things is that because there is not a 100 percent HTTPS yet, uh, the malicious gateway can still inject stuff into, into the HTTP pages. So we can, we can get the user to visit our malicious web page and then start messing with our browser.
Uh, for example, captive portal pages which I’m sure everyone has encountered, uhm, since they’ve been in Vegas. Okay, so, we came up with a few basic techniques, uhm, that let use do pretty much everything that you’ve seen in the demo so far and in the demos that we’re gonna show you. So one of the simplest ones that works really really well is taking advantages through to vdirect. So, uhm, the idea is that we make the user’s browser visit a known URL, uhm, that’s not sensitive and that URL redirects to sensitive URL with sensitive information that we can then steal.
So, for example, if you are logged into Google and you go to this URL, uh, so plus dot Google dot com slash mesos posts. If you’re logged in it redirects to a u, a, a URL with your user ID in it. So, now we know who you are on Google, uh, the same goes for Reddit – we can get your Reddit username if you’re logged in there.. And, uh, very simple way to do this, uhm, is Literally just to, uh, put let’s say, an image tag, uh, on a page, and uh, won’t be visible and it’s not even an image but the browser doesn’t care or go and request that URL and then we can leak that via, uh, via DNS. So, for example, uhm, that would be sent to the attacker would get the username for Facebook.
So that’s the first technique. The second technique, uh, we’re gonna use, uhm, which you’ll see in a demo is, uh, soon. is dealing with kind of, one time auth tokens, so perhaps we, you know, do this, uh, redirect, uh, so the user’s browser redirects to a URL we can leak the token but the problem is the attacker wants to use that token and if the user’s browser get that first then that token’s no good to us anymore, if it’s a one time token. So the attacker wants to use it, they want to stop the us, the victim browser from requesting it. So the PAC scripts, uhm, as well as just leaking the data we can say actually if the URL matches this, uh, uh, exact pattern, uhm, then return a proxy that doesn’t exist the user’s browser won’t be able to, uhm, resolve the proxy that URL won’t get fetched but we can still leak it to the attacker to use that data. Now the third trick we came up with, uhm, which was, was which quite fun, is um essentially what we want to do is get, uh, load a page that the user is logged into and that page will have loads of, uh, stuff on it we want to get.
And it will be loading lots of URLs that we want to, we want to leak. But we don’t want the user to know that this is happening, uhm, so… Uh, in the past things like iframe should be really good for this we could quote a, a tiny invisible iframe, load the URL in there and we’d get all this, this stuff loaded. Uhm, but iframes tend not to work these days because most sites use the X-frame-options which says “Don’t allow this site to be framed” so we came across, uh, something called “pre-render”. So pre-render is something that Chrome, uh, uhm, invented first, uh, and is now Edge as well. Uhm and essentially what it does, uh, assist HTML type here and what it says is “Uh, completely load this page in a kinda hidden, in a hidden window, uhm, offscreen. Uhm, load it so it’s ready so when the user actually clicks that link it’ll all be pre-rendered and ready to go and it’ll appear really quickly.” So, uhm, like Google uses this, uses this, so the first often the first hit on a Google search results will be pre-rendered so when you click it it looks like it just magically appears really quickly.
Uhm, so what this, what this lets us do is, uh, load a known URL, uhm, that fetches other sensitive stuff. So for example, if I load, uhm, your Facebook photo album or your Google photos page, uhm, it’ll go and request, uhm, all the thumbnails of all your photos, uhm… Now these, uh, these URLs, uhm, are always on CDMs so they’re over HTTPS but they’re not authenticated at all so they have these long, random-looking URLs which are impossible to guess. Uhm, but if we tear that URL and, uhm, load it in another browser, uhm, you don’t even need cookies, you don’t need to be logged in… you can see, you can, you can get that data. Uhm, so pre-render’s good for that and you will see, uh, some demos of that in a sec. Right, over to you… >> Good, so let’s see if we can, uh, we can, uh, see this in practice. So, find RDM again, so in this case we have the, uhm, same as before – the user’s there but, we’ve, uh, we’ve managed to force them to a, a webpage we control and are able to inject content into.
We’ve chosen a particularly complicated, secure, uh, captive portal so we’ll be on there for a little while. On the attacker’s side we can, uhm, we can start the attack so hopefully if I click this button here we’ll start to see, uh, information coming back from that user’s browser session so we’ve already been able to grab their, uhm, Google ID, Facebook ID and name from Google. >> Hope it’s working… >> This is where we cross our fingers and hope the next bit works. >> Yup. Yea… come’on. You can do it! >> Fine! So it looks like, uhm, pulling the google images hasn’t worked this time. >> Show the video…
>> Uhm, I might rerun it. But we can also, you can also get their Twitter ID, uh, LinkedIn ID and their, uh, employment from LinkedIn, GitHub ID. This, I mean this, I mean this is just a really small subset of, of services we were querying here. Uhm, but, there’s a lot lot more we can do with that. I’ll just try rerunning it – see if we, see if we can get anything else or not.
But essentially that allows any captive portal to completely denom, deanonymize the user. Here we go! The images as well… Deanonymize the user that’s connected, connected to their gateway and get all sorts of what we would call, I guess, public but sensitive information about that user. Uh, and you can see we can also get onto these images. Uh… Oops, we can achieve a full-sized image just cause, cause it’s served on a, from a CVN, they’re all there. And we can, we just grab those files, and, and, kind of get all that offline data from them. So… number two! We, we’ve done well so far! So, just, just to summarise that… so, uhm, if you force the user to, uh, request a webpage or URL we can get identifying information from it, we can then use that, uh, those IDs and usernames to kind of get further information.
So it’s a bit of a, bit of a cycle going on there but that’s kinda the overview of, of how everything works. So kind of getting the information about who somebody is is good and we, we were chuffed with that. We thought “Right, we’re really on to something!” But we can do better. And so we kinda… doing this research over a period of months and kinda just, these things, ideas are coming up so as, as we’re going through. And one of the things we were quite interested to look at is, is OAuth. So, uhm, OAuth for those who don’t know, is a, a way of allowing a third party to authenticate users to your website. So there’s some, some really OAth writers, Facebook seems to be one of the biggest, uh, Twitter, LinkedIn, Google, Yahoo, Microsoft, and these services allow websites to hand off the authentication to these essential authorities.
So, you, you would all have seen it “Sign-in to this site… Sign-in with Facebook, sign-in with Google”. Uh, you just click those buttons, if you’re logged into Facebook or Google automatically you’re logged into that site without having to type in your username and password. This is, this is great from a, from a usability perspective you don’t need to remember another set of credentials – it just all works. Theoretically anyway… Uhm, OAuth has a number of ways of passing tickets and, and tokens between the, the, I guess the client application and the central OAuth server.
Uh, but one of the more, uhm, common implementations i, uh, using URL parameters via, through 3 0 2 redirect over HTTPS. So, we thought can we force this, uh, users to attempt to OAuth authenticator, large range of services intercept the, uhm, the final authentication token and replay that ourselves. And that’s something we’re also gonna attempt to demonstrate. So, again, users still here, trying to fill out their, uhm, Uhm, their form password overtake. They’re gonna be there awhile, uhm, so we, we kicked off the next attack and you can see this one’s particularly quick. It’s a roamer using 3 0 2 redirect, we’re not trying to do the pre-render pages which we have to do in serial, so, only one at a time. This, this is going quick – lighting fast! Uhm, from the, from the attacker’s console we have now got all of these potential, uhm, OAuth sessions, so if I for example open coded and then an incognito window, theoretically… good, that bit worked. Yip! Brilliant! I’m now, now logged into, to codepen as a user with that, uhm, bin, bin on there…
Keep going, we’ve got loads of other services, so for example developed on Mozilla, got that account, someone’s interested, dunno if anyone’s used ForShared before but, it’s a, uhm, cloud storage platform so we can grab that and then start grabbing their files from, from that platform. And we’ve got full control of these accounts at this point. So, uhm, we’re just logged in as if we were those users. Those are going well now… >> Yea. >> Alright! S… So back to the slides. So this is, this could be done passively, we could wait for the user to log in but, as Paul mentioned, we’re kind of impatient. So we can force this and you. if you’re using the 3 0 2 lookups you can actually force, uhm, a large number of, uh, authentication attempts against a large number of services very, very quickly. Uhm, the user won’t say anything necessarily when they, uhm, go to log back into that service.
Uh, they, in our experience they haven’t, they won’t see “Failed login attempt” to this or anything else. So, it, it’s pretty blind from the user’s side of things. And it does allow attackers to gain full control over the victim’s account. >> Okay, so, uh, we’ve shown you a few demos, which we were quite pleased with but we wanna go even further, so, uhm, we wanna, so we’ve to learn some of the, uh, kind of, uh, accounts the Facebooks doesn’t care about, I mean, they tend to use OAuth for things that you just can’t be bothered to create an account. But we wanna go after the, uh, the good stuff.
So when they attempt to get into your Google account now. So, uh, the way that, uhm, Google works is quite interesting and they’ve got lots of different domains. And, you can’t share cookies between top-level domains. So, what happens is when you log into Google, uh, most of your cookies, uh, go up to the main Google dot com domain and, uh, when you go to another website, like YouTube or Blogger or one of the regional Google search sites, uh, then, uh, there will be a kind of first party SSO, so, uh, we use, uh, the say Google dot co UK will ask the main site, uh, for an auth token and it will use a 3 0 2, 3 0 2 redirect so we can steal that. So, like this, uhm, so we’d go “accounts dot Google dot com; please log me into Google dot co dot UK” and it’ll say “Okay, you, you’re logged in, that’s fine; here’s a redirect, here’s auth token”.
And it will go and set the redirect on the, the local site. So, uhm, and then you’re logged into Google dot, Google co UK. Kay, and… uh, ah gee! Uh, the second thing, the second demo we’re gonna see, uh, is, uh, stealing stuff from Google Drive. So, again, when you download stuff from Google Drive there’s a few different ways it worked depending on how you got the file, uhm, so we’re looking in this case at files which have been emailed to you and that you, uhm, saved to your Google Drive. Uh, so, uh…. What happens when you, uh, clicked download the document? Uh, as you start off from “Drive dot Google dot com” uhm, and then it redirects to a redirect to “Google user content dot com” which is, uhm, uh, unauthenticated but uses uses and auth token. Uhm, and it kinda does this, uh, kind of redirect back and forth between the two different sites. Uh, eventually we can get the auth token essentially, uhm, and download the documents. So, I’m gonna show you, uh, that domain…
Uhm, I should point out that none of these are vulnerabilities in, like, google or any of those. So of all sites, this is just, this is just because, uh, we can, uh, steal the HTTPS URLs. Okay, so we will click this button and we’ll see… there we go! So, uhm, we can see the URL here has got the , uh, uh, the auth token in it and all I’m gonna do is literally just open that URL in a private browsing window… So, there we go, I’m now logged in to Google dot co dot UK. So, like I said, this isn’t your main Google account, uhm, we haven’t got, like, the crown jewels but we can still do quite a lot of stuff.
So if I search for, like, uhm, my email… I can’t type… Uhm, so we get a summary of what’s in your gmail inbox, I can’t click on those but, you know, I can still see, yea I see a summary, I can view my photos… uh, I can do my home address, there we go. Uh, I can do my location… Uhm, my location isn’t working… Okay! Uh, but, another thing we can do, if you, if you happen to have, uhm. Location history turned on on your phone, uhm, then Google is basically tracking you everywhere you go. And… because, uhm, google maps is, kind of, again, regional – it’s not the main Google dot com site, you can get your timeline. Come on! Please start working. So you can see everywhere we’ve been in Vegas. All the best places we’ve been…
Uhm, and so, uh, where did we go today, ah, it’s being a bit slow but anyway. Uh, we thought that was quite nice. Thank you. Yea, right, we’ve gotta get on. Okay, so I’ll hand it back to … >> You want to do the Google drive demo quickly? >> Oh, Google drive, yes! Thank you, right. Uh… okay So Google drive, click the last button, and hopefully we some stuff popup. Here we go, so you can see all the URLs going through the bottom, uh, now the attacker’s server is going to download those, uh, to the server and then we can load some of these things. Did? How did you get… Alright, uh, so yea, so you know, if you’ve added some passwords to your account, some pdf. Uh, that’s someone else… Uhm, that’s some passwords there. Right… >> Great! So that last demo, that’s, that was all Paul’s work. Uh, he spent ages doing that and I thought well I can’t let him have the best demo this talk. So, I spent a little while looking around and thought I’ll try Facebook.
There’s got to be a way to get into somebody’s Facebook account, right? And… there was! And up until about three days ago this worked. It was only when I went to record a video of showing stealing somebody’s Facebook account using, uh, OAuth that it all stopped working and Facebook broke it. So, I don’t have a demo of that I’m afraid, uhm, Facebook didn’t break it in the sense that they fixed it they just broke it.
So, the attack was through the forgotten password functionality, there’s an implicit authorization between Facebook and Microsoft’s OAuth. So if you’ve signed up to Facebook with a Microsoft account you can hit, uhm, forgotten my password, type in your email address and as an option to just… reset it via the OAuth authentication to Microsoft. Uhm, but that now asks you to log back into your Facebook account so it’s a reset your password, you have to log into your facebook account. Anyway, uhm, so I’ll move on from that.
So one of the kind of key points we thought we were gonna get from this is people turning around and saying “So what I use a VPN?”. VPNs allow us to kind of travel safely over hostile networks and, uh, kind of should protect us in this and this area. Right? So, just to go back to our previous examples, so, let’s just, uhm, gateway, uhm, with the user’s connection over a VPN user channels through to that VPN ser, server and then all traffic gets out to the, to the, uh, intercept from that VPN server. So the attacker can’t sniff HTTPS URLs or they can’t intercept traffic. Using the PAC break, similar sort of thing, we tell, we tell where the pack file is, they’ve got their secure tunnel set up but the PAC is situated on the local network. There’s no route from the VPN server to, uh, to where we’re hosting the PAC file and then the user, because the user browser can’t find the PAC file it’ll just ignore it and disconnect directly off of the internet. So what if we moved the, uh, web server hosting the PAC file to the internet? So we, so we, tell the, uh, the client that the PAC file is on an internet accessible, uhm, server, they connect to that VPN server, they can now access that PAC file and connect to the internet.
So, at this point we are sniffing the URLs as we were before but we can go one better than this. What are PAC files supposed to do? They’re supposed to specify a proxy, so if we stick our proxy server on the internet as well… we’ve now got the user’s traffic coming out of that VPN endpoint leaking the, uh, HTTPS URLs to our, to our DNS server proxying all of their HTTP traffic before it’s even hit the intended, uhm, the intended target. This kinda blew my mind, this is really quite cool! Yea…
Shouldn’t work like that, should it? So, many VPN clients do not actually clear the proxy settings obtained via their WPAD. Uhm, we tried a few and I’ll run through this, uhm, shortly. Uh, the, the traffic’s travelled all the way from the VPN end-point through our proxy on the internet before it hits the, uhm, the intended destination. So, the effect itself on this…over VPN is effected. They are working on a fix but to this point it has not been released…
Uhm, and this, so there’s no way of mitigating this through an open VPN server configuration. “Private internet access” I dunno who uses private internet access in this room for, uh, for VPN configuration… Uh, we reported these issues to them as well as open VPN they have fixed it… so they are based, uh, uh, their client’s based on open VPN but they’ve been implemented client’s site fix to disable the really bad, to kinda, to kinda fix this. Uh, and, uh, kinda more corporate, uh, VPN solutions for example Sysco only connects, actually have an option to say push your own proxy or kind of completely wipe all proxies settings before, before coming this way. Uhm, the windows built in VPN clients aren’t vulnerable to this, they actually looks like they’ve thought about this issue and have disabled the WPAD by default on these.
L2TP and PPTP, uh, connections. Yea, oh, yea… This picture is, uh, Paul’s third work of art there, the rejected vulnerability title for, for this issue. Uh, so the next response “So what, I don’t use Windows?”. Uh, yea, actually other operating systems do use pattern PAC so… OSX does, iOS does, Android does. Okay, not by default, so it’s not quite as bad as on Windows but you do need to be aware of it. Uhm, I think that’s pretty much everything I covered. Yea… So, to mitigate this first thing you do on a Windows system is you turn off the WPAD. Seriously, turn off WPAD… Because, there’s no, there’s no good reason to have it on. So if you still need to use PAC, which a lot of organizations will, will need to do. Turn off WPAD… And configure an explicit URL for your PAS script so you can do this securely over HTTPS, uh, to an internal server or you can actually save it from a local file in Windows if you specify another registry key.
So we’ll just put it from the, the, uh, from the disk. And those are really the only two secure ways of, of doing, or distributing PAC files. Uh… to mitigate the VPN turn of WPAD! Only so many times you can say that… Uhm, VPN is safe if WPAD is enabled, uh, if the VPN environment requires a proxy server to get out to the internet then it effectively mitigates this issue. We can’t chain proxies using, using PAC as far as we’re aware. Uhm, or if the VPN server pushes in explicit proxy configuration the this, this won’t be an issue and that’s certainly an option on enterprise-level VPN solutions. So, the good news! We reported this issue to, uh, vendors back in March, and, uhm, and a lot of them have fixed it so Apple came out pretty quick, uh, releasing fixes, uh, for OSX and iOS, uh, and Apple TV.
Didn’t know they still did that but… Uhm, Google Chrome patched, just a few weeks ago. In fact I was setting up these demos and I couldn’t work out why they weren’t working the other day, it’s cause my, uh, my Chrome had automatically updated and I just had to downgrade it again. Uhm, Android patched, patched in July, uh, FireFox – waiting on a patch for this issue but it’s also not the default configuration if, in Firefox. So, it has to be explicitly enabled, uh, and Microsoft, uh, kind of a patch pending, again slightly different on Microsoft, certainly on, uhm, on Edge on Windows 10 it does some really funky caching stuff so, it’s really not quite as big as, as big as it deal with that. How long we got? We’ll run through it – two minutes. So we were actually not the first people to, to spot, to spot this issue, but we were the first to report it. So, there was a talk at Black Hat this year, literally last week on this exact same issue.
Uh, the guys didn’t report it to any vendors, for some reason. Uhm, the, then this, hope I’m pronouncing this right: Bas Venis, uhm, reported this issue to, to Google and FireFox literally two weeks after we did, uhm, so plenty of people looking in the same place. Uhm, there was a master’s thesis, uhm, from may this year which outlined this issue, uh, there was a Russian blog post from June last year outlining this issue, and there was a StackOverflow question from May last year outlining this issue. Lots of people have found this, nobody reported it to the vendors… interesting. Uhm, not sure if we got time for that slide… So, to summarize network based attackers can inject PAC scripts into browsers. PAC scripts can leak all HTTPS URLs via DNS to an attacker, at least on unpatched systems. We showed how to deanonymize users; steal OAuth tokens; access photos, personal data and documents. VPN wouldn’t necessarily prevent you from a malicious proxy…
No go turn of WPAD! >> Uhm, very quickly I just wanna say we’re gonna be releasing all the code for all the demos, uhm, like, as soon as we get back home and have had some sleep, uhm, so, it’ll be on GitHUb. Just watch our Twitter feeds and we’ll let you know when we’ve released it. If you’re interested. .