Exclusive Interview: Hacking The iPhone Through SMS

We recently chatted with security expert Charlie Miller from Independent Security Evaluators about the recently-disclosed iPhone vulnerability that would have allowed a malicious hacker to take control of an iPhone through a series of carefully crafted SMS messages.

Alan: Thanks for taking the time to chat, Charlie. Why don’t you start by telling us a little bit about the SMS vulnerability?

Charlie: The iPhone bug has to do with telling the phone there is a certain amount of data, and then not sending it as much as you said you would. The function that reads the data starts returning -1 to indicate an error, but the other parts of the program don't check for this error and actually think the -1 is data from the message. This shows how complex it can be to write secure code, as separately, each part of the program looks correct, but the way they interact is dangerous!

Anyway, depending on what you send, different bad things can happen. At one point, you can get it to exit because it is about to allocate -1 bytes (which is viewed as 0xffffffff--a very large number). This is a denial of service that will knock the phone off the network temporarily.  

During my BlackHat talk, we kept sending this denial of service message every 10 seconds to a volunteer from the audience to keep him off the network.  As an unfortunate consequence, the messages were getting cued up on the network and his phone was still getting knocked off hours after the talk. He has since gotten back up and running.

Alan: Note to our readers: whenever Charlie says he needs a volunteer, don’t make eye contact. So, how did you send the message? Were you sending it through the SMS interface of another iPhone or doing something like emailing the “telephone number@attwireless” approach?

Charlie: To send the SMS over the carrier network, we had a small application on our attack iPhone that would talk to the modem using GSM AT commands. For testing and finding the bugs, we used this really cool injection framework that my co-presenter Collin Mulliner wrote, which lets you test SMS message implementations by only sending data over TCP. This prevents you from having to send data over the carrier network and doesn't cost anything, and also lets you test many messages very quickly.

Alan: So how do you go from a denial-of-service to a full-on exploit?

Charlie: The worst case has to do with how the program handles concatenated messages. This is a way to send more than 140 bytes at a time. You can send a long message in a series of messages and the phone will reconstruct it into a one long string. It accesses an array based on a value from the data. In the case where it thinks it reads -1, it actually accesses the memory before the array, not in the array. By setting things up just right and being tricky, you can actually leverage this to gain complete control of the device.

The entire attack takes just over 500 messages, although the victim doesn't know they are being sent because they don't show up on the phone. Most of these messages have to do with setting things up "just right." Sixteen of them actually access the array out of bounds.

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  • burnley14
    Wow, don't make Charlie angry. He can take over your phone remotely and kill you with it.
  • ethaniel
    Unless he hacks Chuck Norris's iPhone. That would be the end of him. :P
  • ossie
    As usual, mr. Charlie "no more free bugs" just likes to overemphasize his findings - free advertising is always great - but it seems his greediness isn't finding the proper nourishment (read cash from blackmailed manufacturers).
    Crashing an equipment is one thing (getting easier in these days of consumerism induced fast paced "innovation"), but taking it over is in a whole different lot.
    Why didn't he demo the iPhone takeover code at BH? I'm sure he would have liked to really impress the audience, but, as it needs a lot of very careful setup, the chances for failure would have been way too high. There are a lot of unexpected events which could have taken place in a real environment (read through the network), as opposed to a laboratory environment (frame injection without external disturbance), which would impede the "golden sequence" to reach it's victim in the desired way (out of order message delivery is just one, which comes quickly to mind).
  • downer88
    ethanielUnless he hacks Chuck Norris's iPhone. That would be the end of him.

    Chuck Norris doesn't use a phone, he uses his "outside" voice!

    Seriously, no offense but I though mobile phone exploits were nothing new.
  • Anonymous
    This should be considered a nice and very credible rebuttal to the ridiculous interview with Joanna Rutkowska... Charlie is a real security expert, and he says Mac security sucks. Take note, Apple fanboys.
  • steiner666
    downer88Chuck Norris doesn't use a phone, he uses his "outside" voice!


    and of course "jailbroken" iphones couldn't take down a network, how stupid must ppl really be to believe Apple/AT&Ts shit
  • anonymousdude
    Charlie_FangirlThis should be considered a nice and very credible rebuttal to the ridiculous interview with Joanna Rutkowska... Charlie is a real security expert, and he says Mac security sucks. Take note, Apple fanboys.

    The safety of a Mac lies in its market share. Less market share less atacks,viruses,trojans, etc. That's why people using linux hardly ever have a problem with security.
  • Anonymous
    anonymousdude: Linux has all but idiot-proof security, low-level exploits are very difficult, there are package repositories that have everything you could ever need without resorting to potentially untrustworthy 3rd party downloads, and they were doing Microsoft's UAC long before Microsoft, and far better and less annoying. Not to mention, they have a far better scheme for handling execute bits and possible remote execution of arbitrary code. An OS is only as good as the idiot who's using it, but Linux has done by far the best job of idiot-proofing an OS, if it hits 99% marketshare, it will still have a fraction of the problems Windows and OSX do, and there are viruses for OSX, ask Apple who recommend MULTIPLE antiviruses be installed on Macs. Out of tens of thousands of free, open source Linux packages, there are hardly any antiviruses or firewalls even available for Linux, because it is actually for real, not necessary. No shit...
  • Anonymous

    OS X is built on UNIX the same as Linux. Please do some research before you spout about things you obviously no nothing about. Otherwise quite wasting the time of everyone that reads the comments.

  • Anonymous
    rorosdad: Obviously you know nothing about UNIX or Linux or the inner-workings of OSX. UNIX operating systems follow a standard called POSIX. There is quite a bit of room for differences in how they are implemented. The BSD kernel OSX stole is not the same kernel that Linux uses, besides, most of the security doesn't necessarily happen in the kernel, user interaction happens in the desktop and window managers. Is there package managers for OSX like Synaptic or Adept? Is anybody at Apple smart enough to thwart low-level exploits, or do they only hire "trend-settings hipsters" to be developers? You obviously don't know much about OSes, maybe you should try to educate yourself before acting defiant to me.
  • Anonymous
    @rorosdad: So let me see if I understand your logic correctly:

    UNIX is an OS standard developed in the 70s

    Linux and OSX are both based on UNIX, therefore:

    Both must have equally good security, and:

    It doesn't matter how much OSX's developers suck, because if they screwed anything up, it wouldn't be UNIX anymore, because UNIX is perfect and unhackable.

    If I'm not mistaken, isn't Charlie Miller(subject of this interview) a hacker famous for pwning OSX? Do any of his exploits ever work on Linux? Hasn't he been quoted as saying that Linux and Windows are both much harder to hack than OSX? Isn't Apple's uber-shi.t Safari browser a liability in itself?
  • matt87_50
    "Charlie: I found the bug by sending in thousands of malformed SMS messages to the device, a process known as fuzzing."

    Apple's QA should have done this, this is similar to a Soak test, QA's bread and butter.

    oh and i'm sorry, what? "I can't fault them too much, it was hard to find". yes it would be hard to find, but to call it in the first place and not check the return type? to code it in such a way that it will only work if there is no error in the SMS (expected size == actual size).

    If i was worried about security at all, I would NOT buy a device coded like this. trusting a hardware buffer overrun protection system to handle all your problems? just pathetic!

    Good to see him call BS on the apple jailbreak argument!
    while I bet apple was all too happy to take his advice on how to patch the iphone, they will just ignore him on this point.
  • Anonymous
    @Synonymous Dude

    "...but Linux has done by far the best job of idiot-proofing an OS..."

    Yes, typing "tar zxvf blahblahblah-1.1-x86.gz cd /usr/bin/blah" is so "idiot-proof" that everyone will be doing it.
  • Anonymous
    vitalDude: Last time I checked, most distros come with a WinRAR-esque utility where you can double-click, extract, etc... Just like you would in Windows, although if you're talking about installing stuff with GNU Make, I doubt most Linux noobs would be installing stuff outside of package managers.

    Epic fail.
  • sdbryan
    rorosdads_dadrorosdad: ... Is anybody at Apple smart enough to thwart low-level exploits, or do they only hire "trend-settings hipsters" to be developers? ...

    It seems that you have never been to a Mac developer conference. I only bother to make that observation because the comment about "trend-setting hipsters" in reference to Apple's Mac OS team is so comical. It might be true about marketing people at Apple but it was easy to observe that as the api level got lower, the engineer from Apple got larger (wider rather than taller) and more disheveled. [Obviously being a trend-setting hipster was not a criterion for choosing personnel]. Any technology company that has been a significant player for well over thirty years is going to have its ups and downs but it is absurd to dismiss its engineering bona fides.
  • Anonymous
    sdbryan: Apples engineers are so good that they failed at writing their own OS, so they stole BSD because it was literally the only thing they could steal and then make closed-source. As a byproduct of this, they don't even have expertise of their own OS. The Windows API is pretty slick since .NET came out, but since not even Apple properly understands the inner-workings of OSX, they have buggy APIs, which is why nobody can properly port an application to OSX, anything that is cross-platform runs 1000x better on Windows, and much faster.
  • Anonymous
    @Ive_seen_the_promised_land: WRONG! OSX originated from NextOS which was an operation system developed by Steve Jobbs's break-away company called NextStep. The monolithic/micro kernel hybrid and base libraries come from a merged NextOS and BSD. The BSD libraries in use were not stolen and still remain open source. Apple help to maintain these libraries. The rest of the operating system including the UI is based on NextOS. NextStep merged with Apple. Many of the designs by NextStep became the modern day Apple designs. The Windows API is not slick - just look at the object model... hideous. No one ports windows applications to OSX because .NET "point and click" programmers can't program in an environment that is not "Visual" nor can they comprehend Java, Objective C or any other slightly intellectually challenging language like Ruby or Scala that allow you to program in a non-imperative way. Recursion? What's that?
  • Anonymous
    bottoms: If I understand you correctly, you're saying that Visual Studio makes programming entirely too easy? Of course, that kind of pointless elitism is consistent with Macs and their users. I'm a MS-hating Linux fanboy, but I can admit that Visual Studio raised the bar for IDEs, it is hard to use something lesser after you've used VS. Thankfully, there is Monodevelop, so I can still write C#/.NET apps in Linux without having to resort to more archaic IDEs that require ninja-like concentration skills for the entire coding session.