字幕表 動画を再生する 英語字幕をプリント So my name is Bogdan Alecu. And the topic for today will be "Business Logic Flaws in Mobile Operators Services." For those that don't know me, everything is about me. I work as a systems administrator as a day job. And during my free time, when I have it, I like to break into a lot of mobile stuff. I started on this particular journey a couple of years ago with GSM networks by using my old Nokia phone and continued with voice over IP and got to GSM and mobile phones. If you want to keep in touch with me, you can find me on Twitter or on my Web site. So the goals for today would be for you to have a really high overview regarding the SIM toolkit. What it is. How we will exploit it. Then a couple of business logic flaws I've identified on some carriers. And I think you're going to find them really interesting. And also in the end if there is a way to protect you from this that I'm going to show you. We're going to call these HTTP headers, data traffic, extra digit and a summary at the end. So who has heard about SIM toolkit? Okay. To keep it simple, think about it as a platform for the carriers in order that they use it in order to install applications on your SIM card. This is how SIM toolkit looks like on an Android device. On some other devices you might find in them like an extra menu with the carriers namely like Orange, Vodafone and so on. And from this SIM toolkit menu, you can find things like exchange rates, the weather, how is the weather like or calling customer support. So different activities. And if you think about it, it's a pretty good thing. Because you have these applications on your SIM card. And no matter what phone you use and you put your SIM card in, you'll still have this application. So you don't need to install anything else in order to have them. Since this application sits on your SIM card, the carrier has a way to update these applications or modify or delete them and so on. So for example, if the customer support number changes, the carrier will send an over-the-air update which is basically a text message to your SIM card saying that the SIM card should update the phone number for the customer support. This message is kind of special message, a comment message. And in order to have this comment message, they may use the SMS of the user data header. The same user data header is used in cases like when you go over the 160 characters limit and do concatenated messages. So you have two messages which are concatenated into one message. And this makes use of the user data header and of course also in cases for -- who remembers the old Nokia ringtones? They also used user data headers. This is how the comment packet looks like for such a SIM toolkit SMS. So as I -- you have the user data header, then other fields like comment packet, link comment, header link, security parameter indicator and so on. The most important one that I want you to keep in mind this security indicator. The number you see below represents the number of bytes each element has. So this -- all of these specifications can be found on GSM specs. In order to also have this comment, you also add other two important fields. Data coding scheme and protocol ID. By setting the protocol ID to 7F, it means that you do a SIM data download and data coding scheme to F6 means that this type of text message is directly addressed to your SIM card. So according to the GSM specification, what will happen when you receive such a comment message, the phone will transparently pass this SIM message this comment message through your SIM card and will not alert you in any other way so basically when your carriers sends this message saying okay I want to update the number for the customer support, you will have no idea that you have just got a text message. And I told you keep in mind security parameter indicator. So you are setting this comment. But you need some kind of acknowledgement to know that this comment message has been received. And this is called proof of receipt which can be set in the first two bits. If you set it for example to 01 it means you always want to get a proof of receipt. So no matter if there was an error or there wasn't any error, you will always get a proof of receipt. And how you get it, you set it in the bit number 6, and there are two ways of getting this proof of receipt back. By SMS submit which means by a regular text message which is sent by our SIM card or by SMS delivery report which is like a delivery report when you send a text message and you want to know if the target person has received your text message. So again, we have this structure. And we need to fill in the elements. The user data header the protocol ID, the data coding scheme I have presented you. And then the others. And as you would imagine in order to make this update of the customer support number, you need to have some proper security keys. But if you look at this example, you will see that ciphering keys that are KIC are set to zero. Because I do not care about ciphering keys at all. Why? Because of the security parameter indicator. If we drill down to this security parameter indicator you will see the first two bits are set to 01 meaning that I want to get a proof of receipt, always get a proof of receipt. And I want to get it by text message. So basically when -- if I'm going to send this text comment message to you, what will happen, it will get to your phone. The phone will pass it to the SIM card. The SIM card will try to execute it. It will see that I don't have any proper security keys. But in return, it will send me back a text message without you controlling it, without you even knowing it. And in order to make sure that how the things are like, here is the screen shot of a wire shark capture. And as you see the comment is to send short message. It has been initiated by the card application toolkit so it wasn't a human initiated action. So SIM card automatically replies to the sending number. There's nothing in your inbox, nothing in your outbox. Basically you will have no idea that your SIM card has just sent a text message back to me. Only if you look at the -- on your bill, on your call records you will see that sometimes your SIM card has just sent a text message to someone. So let's see it in action. so here I have the destination number. I have the user data header. The binary data, the fields that I filled in. The protocol ID and the data coding scheme. And I have the target's phone. On this phone, this is a prepaid phone. And there is -- it's balance is zero so I have no credit on it. So it will try to send a text message. But since it has no balance, I will get a text message from the carrier saying: Hey, you don't have any credit. You need to refill. Now, once I submit this, it says sending. And there is no way to stop this. I can't push any button. The SIM card just sends -- tries to send a text message. You cannot control it. It keeps trying to send if I had a look at it I would have -- if I hadn't looked at it I would have no idea I just did this so if it's in your pocket you will have no idea your SIM card is trying to send a text message. And I also got some text messages from my carrier saying you do not have enough credit for sending SMS to this number. Please recharge your account. But I didn't send any text message by myself. The SIM card tried to do so. So maybe you will think that okay maybe this is not something -- I don't know -- important let's say. I can make your SIM card send the text message back to me. Well, maybe that's not a big deal. But let's think on some other way. Let's say there are services that allows you to send a text message from any number. So you can send someone a text message coming from whatever number you want. Now, let's say you also have a premium rate number. International premium rate number and you send a comment message coming from the premium rate number to some target phone number. What will happen, the target phone number will send back a text message to the premium rate number you have. So you're paying like a couple of cents for sending a text message. And in return you get 20 times more. So it's a pretty good conversion rate, right? And the target phone as I told you, some phones don't even though that there is a text message sending in progress. Even if you keep your eyes on them. So until you will get your monthly bill, you have no idea you have just sent text messages to premium rate numbers. Now let's talk a little bit about HTTP headers. The easiest way you can think about them is by identifying the browser you are using. So if you're browsing from Firefox let's say, that browser will have HTTP headers if you're browsing from Safari it will have other headers and so on. Now, with this in mind, there are some -- most of the carriers have a mobile page where you can find your balance, you can change your services, you can download ringtones, videos and whatever. This page addresses using am.carrier.com so the carrier name. If you try to access that page from your computer you will most probably get something like this. So they will detect that you're not connected to their network. And they will tell you: Okay, you have to connect to our network in order for us to show you the page. But in some cases, if you pretend to be browsing from a mobile device, they will display this page. So what I did was to use Firefox extension called user agents feature. And I identify myself as a Nokia 871 phone once I did that I got the display page the mobile page of the carrier. But it was just a general page because I was not authenticated so I could not see any balance. I could not download any ringtones. I couldn't do anything. Well, this is how -- the things where they start to get interesting. The operators, the carriers know how to charge based also on HTTP headers. So the idea was to well sniff all the traffic my phone does and see if there are any HTTP headers specifically in my phone number. But I failed that. Because there weren't any HTTP headers. Then after some monitoring I found a research paper called privacy leaks in mobile phone Internet access where he noticed that when someone from a mobile device was accessing his Web site, that carrier was also sending the phone number. So he did a list with all of the HTTP headers that the carrier was sending. And published it. And the carriers no longer -- are no longer sending these HTTP headers. Okay. So they are not sending the headers. But what if I will inject the headers in the traffic? So I chose a couple of HTTP headers which identified the phone number. And as their value, it is the phone number in international format so with the country code. So now I can access that mobile page of the carrier from my computer by identifying myself as a mobile device and I can also authenticate myself by injecting these HTTP headers. And what happens now? I can see anyone else's balance. I can change their subscription plan. I can reveal any other account. And stuff like this. Whatever carrier allows me to do so. And some carriers are even tieing up the phone number with the bank account so you can even see the bank details of that specific customer. But I didn't stop here. Remember when there was a time we had to call the Internet with our phones? Well, I was surprised to see that there are still carriers who still have CSD. So think about it just like a dialup connection from your phone. So the carrier has the dial-in number. You set up a dialup connection from your phone to that number. And you're browsing the Internet with 9.6 kilobits per second around 1 kilobyte per second pretty good speed right? But since it's just a phone call it also has the vulnerabilities of a phone call, which is are caller ID spoofing. Now, guess what was my reaction when I first set up that connection to a Voice over IP provider which was spoofing my caller ID and then forwarding the call back to the dial-in number and I was authenticated. So this is just the target phone. The screen of the target phone. And also I have connected mobile phone via Bluetooth because I want to have a GSM modem attached to my computer. So first I'm calling myself on my own number. With my own number. So this is what it means own number. So this works then I'm making up the connection as you see I'm using a pretty old Nokia phone and I'm connected to the carrier's network. What is the goal of this? Is, well, if I do the caller ID spoofing will I be authenticated like any other user and incur charges to that target account? So once I'm registering to the network, I'm going to check for my balance in order to see the initial balance and the after attack balance. So the current balance is 6.05 euros. Next I'm going to choose something to download. And I'm choosing some image.