Android and iOS devices are today a prime target for hackers, and for a good reason, two of the main factors of the perfect attack are combined while exceeding any of the attacker's expectations.
This article is about the ironha1l Tool Suite I have created. This article is intended to provide an understandable explanation about the problematic I faced during my research to develop ironha1l. You will also find in this article a lot of relevant information if you are a jailbreak beginner. Most of the information here are part of my own research but also comes from external sources. I tried to remain as reliable as possible. Feel free to comment my work!
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- 10/10/2012 – ironha1l sources available!
Why attacking smartphones with smartphones?
The primary factor is the quality and relevance of the information available on iOS and Android devices. Smartphones like the iPhone and the Galaxy SIII to name but a few, have been created to assist a large majority of our daily activities. Consequently, they contain a huge amount of data about our life and habits such as address book, pictures, emails, text messages, GPS location data history and much more. We can also find web browser history and all cache, credentials and data of third party applications such as online banking applications.
The second factor is accessibility, and even more so, the huge amount of attack vectors. These operating systems are mainly used in mobile phone devices and provide many access points for potential attacks. First of all, the mobile aspect of these devices can be used for data injections via the baseband, meaning injections via 3G/Edge/GSM protocols with text messages and voice calls. And even further, some attacks can be made on SIM cards, for example spoofing adapters are mainly used today for unlocking. More wireless access points such as WiFi, Bluetooth, IrDa, NFC constitute a large part of the vector attack panel and can be used to remote access the targeted device. Finally, some last attack vectors such as USB, serial port, SD card reader, audio port, touchscreen and camera provide to the attacker some physical and potentially vulnerable access points.
https://www.youtube.com/watch?v=JTOsiGXnILU
About the PoC scenario and its limitations
The main idea I had about a smartphone security related scenario was to show the two aspects described in this foreword. The revolutionary aspect of these mobile operating systems in term of functionality versus their incredible weakness in term of security. Therefore, the attacker is equipped with an Android 4.0 (Ice Cream Sandwich) smartphone in the aim to access sensitive data of an iOS unjailbroken device such as iPhone 3GS/4, iPod Touch 3G/4G or iPad according to the limera1n exploit limitations. The iOS version does not matter here, as the limera1n exploit does not depend of the operating system version running on the device. The attacker has only one constraint, which is to use the USB port of both devices to inject data and proceed to the data theft from Android. The aim of the attacker is to get the maximum amount of sensitive data available on the iOS device, such as pictures, emails, contacts, etc. The attack must be fast and discreet (a few minutes), and must be cancellable at any time. The use of an Android smartphone as been preferred for these reasons, due to its discretion, offensive functionalities and performances.
In this article, the term iDevice is used to refer to any iOS devices vulnerable to the limera1n exploit.
Bypassing iOS security
Before going further it is important to enumerate some of the main security features available on iOS. The same goes for the architecture security features, particularly the boot process and partitioning system.
iOS partitioning system and its biggest security feature
All iDevices have the particularity to contains a 8GB to 64GB flash memory split in two distinct partitions. The first one in read only contains the operating system iOS while the other one is dedicated to user data and have read and write permissions. The data partition contains user documents, applications, pictures, and other various user files. This flash memory is hardware encrypted using an AES-256 crypto-processor soldered on the iDevice motherboard right on the path between flash memory and RAM. Meaning that anything that comes from the flash memory to go in RAM is decrypted and anything that comes from RAM to go in the flash memory is encrypted. Nothing can transit without being encrypted/decrypted by the crypto-processor, thus you cannot manually extract the flash memory and read data from it, because everything is encrypted with AES-256.
UID (Unique ID) and GID (Group ID) are two keys soldered inside the crypto-processor and used to encrypt or decrypt. These keys are only accessible by the crypto-processor itself, they cannot be software requested or dumped (hypothetically a covert channel attack could do the trick). The UID key is unique for any iDevice and is not registered in Apple Databases (but we do not have proof for that), the GID key is the same for iDevices of the same class, meaning for example that any iPhone 3GS will have the same GID key but each one will have a unique UID key. On top of that, these keys can be combined in addition to the passcode key (derived from the user passcode to unlock the iDevice) or any other external key, which creates various protection classes.
These protection classes are then used to encrypt some user data on top of the already hardware encrypted flash memory. Thus, if you successfully access the data partition, some files will remain encrypted with either the passcode key or other external keys combined to the UID key, which is the case for emails for example. So once the iDevice is locked, files are completely secured due to the missing passcode key. And brute-forcing the passcode key can only be achieved on the iDevice, because the decrypt function is called inside the crypto-processor which combine the given key with the UID key.
According to iOS Hacker’s Handbook it takes about 18 minutes in the worst case scenario to bruteforce a 4 digits passcode (iOS default scheme), which is even worse if the user changes his passcode for a alphanumerical passcode (in that case it can take years to bruteforce). There are no time limitations in case you bruteforce the passcode directly by calling the decrypt function of the crypto-processor. But in the case you attempt to manually bruteforce the passcode directly from the iOS unlock screen you will face these limitations that exponentially increase when a wrong passcode is entered.
Fortunately for attackers, only a few amount of data files are encrypted using the passcode key. Most of the files remain unencrypted, and some protections I talked about here were implemented during the iOS development. Meaning that old iOS versions are less protected that the newest ones, unfortunately the ones I presented here are all integrated to iOS 5.
Various exploits but only one goal
There are three categories of exploits on iOS, each one refers to a particular boot module of iOS.
- Bootrom (also called SecureROM by Apple) Exploits
- iBoot Exploits
- Userland Exploits
Bootrom exploits are the most powerful, because the bootrom is the first piece of code executed on the iDevice boot process. This bootrom is read only and cannot be updated nor modified, it is soldered on the iDevice. Thus a bootrom vulnerability cannot be fixed by Apple on existing and already sold devices. Actually there are only one bootrom exploit, which is called limera1n and created by George Hotz. This bootrom vulnerability has not been patched by Apple until the next hardware revision with Apple A5 processors and upper (meaning iPhone 4S, iPad 2, etc.) only iPhone 3GS/4, iPod Touch 3G/4G and iPad are vulnerable. The limera1n exploit breaks the signature check for any elements of the boot process, meaning you can boot with an alternated or custom boot chain. In addition to that a bootrom exploit can be used to decrypt Apple GID encrypted files contained in IPSW archives (used to restore or upgrade iDevices). IPSW contains iOS and various GID encrypted data, that can be decrypted using with such an exploit by calling the crypto-processor function that uses the GID key. Attackers can then patch and alter these decrypted files for their own purpose, inject and boot with these files by the use of limera1n.
iBoot is the boot process part that launches the iOS kernel. These kind of vulnerabilities can lead to an untethered Jailbreak. Finding a vulnerability at this level is as powerful as a bootrom vulnerability in term of functionalities. Unfortunately such a vulnerability can be quickly patched by Apple in a next iOS update. iBoot vulnerabilities are not used in ironha1l, but it is important to have in mind the entire boot process for the next part of this article.
Finally, userland vulnerabilities are at the top level of iOS at the same level of running iOS applications. Exploiting such a vulnerability is very hard, and only allows the attacker to access mobile (or root) privileges. But yet, the attacker needs first to get out of the sandboxed application where the vulnerability was exploited. I will not talk more about this kind of exploit here.
DFU mode
The DFU mode (Device Firmware Update) is a special mode in which the device loads a specific code from the bootrom. This mode is also available in the Nintendo DS for example, and is not Apple property. This executed code allows the device to accept boot elements from the sync port of the iDevice (I prefer calling it the USB port). This DFU mode is mainly used when the device is software bricked, and even if the classic restore mode of the iDevice is broken. The DFU mode once detected by iTunes will receive boot elements from it. Those elements are from the IPSW archive, and are composed of iBSS, iBEC, DeviceTree, KernelCache and Ramdisk. The ramdisk file is a container which contains a very basic version of iOS only used to flash the device with a new iOS version sent by iTunes. This ramdisk is a very good basis for an attacker to access the iDevice partitions.
To put your iDevice in DFU mode, you first need to connect it to a USB host device, to boot the iDevice while maintaining the HOME and POWER button pressed during 8 seconds, then release the POWER button only while maintaining the HOME button still pressed. After some seconds, the iDevice should be in DFU mode. This mode is visually indistinguishable, only the host device knows if the connected iDevice is in DFU mode as it receives a DFU notification.
In 2012, George Hotz publish his limera1n exploit which allows the use of unsigned boot elements on vulnerable iDevices. This vulnerability is a memory overflow in the bootrom. With such an exploit, jailbreakers are able to modify the iOS ramdisk used in DFU mode, for example by editing the /sbin/launchd binary which is used to launch other binaries and scripts at boot, such as mounting partitions in read and write mode. This launchd binary will be used for example to execute sshd on our ramdisk.
Tumbling down the rabbit hole
* This part is dedicated to the development and creation of the ironha1l and DFOwn tools. Those tools were created to inject and execute a custom ramdisk containing a SSH server on a targeted iDevice using an Android device.*
USB reverse
As previously described, what is interesting for us is to exploit the bootrom vulnerability with limera1n in order to inject a custom boot chain on the targeted iDevice. Actually, jailbreak software such as Redsn0w can do that, but our aim here is quite different as we intend to do it with an Android phone, and there are no such existing tools for this operating system.
We have two choices. The first one is to modify existing and open source jailbreak tools and port them for Android platform. The second choice is to create a totally new tool optimized for Android. Given the aim to have a mastered full tool suite, and because I had time to learn and I love challenges, I decided to give a try to the second alternative. Consequently, USB reverse engineering in DFU mode was required to establish how data is sent to the iDevice and what are the USB transfer modes, headers and commands used for all the steps of the boot chain.
It is first necessary to create an USB debug environment or as I like to call it, a Man In The Middle USB. There are several ways to do this, either you can directly reverse each element of the boot chain to understand how the following elements must be injected, or you can modify the Mac OS or Windows USB driver to activate the USB debug mode, you can also use a sniffer device between attached to your USB cable, or you can even directly use a Windows Virtual Machine on your Linux system. In this last case the use of Wireshark running on Linux will do the trick, as it can sniff USB communications, especially in our case the USB communications between iTunes running in the Windows VM with our attached USB iDevice. This last method is quite buggy, but allows us to see the USB communication protocol quite easily.
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The full description of the DFU mode is in the meantime available in the Universal Serial Bus Device Class Specification for Device Firmware Upgrade publication. With the help of this documentation and various USB headers and requests sniffed with Wireshark, the exact iTunes behavior for data transfer in DFU mode has been established. It is important to note that all communications are in clear text, same apply for commands sent to the iDevice which are associated to each part of the boot process. Another observation, is that header values are specific to Apple and not documented.
Development of libironha1l and ironha1l
The biggest step in this project was to create the ironha1l tool and its library libironha1l. This library provides functions to inject data to the iDevice in DFU mode and is strictly based on libusb. The principal advantage of this last point is the portability of libusb, and its compatibility with Android. ironha1l is the application that coordinates all the various injections of our custom boot chain, based on the DFU protocol reverse established previously. Meaning the injection of iBSS, iBEC, DeviceTree, KernelCache and Ramdisk modified files. These custom files can be extracted and automatically created using the iPhone-dataprotection tool suite of Sogeti.
The development of ironha1l and libironha1l lasted 3 months and contains more than 1000 lines of code. ironha1l and libironha1l are written in C. The ironha1l tool also comes with the limera1n exploit and payload (sources available on the Jailbreak community Wiki).
During the development, a number of difficulties came to light. The first one and the most difficult was the ramdisk size. During the first attempts to inject a custom ramdisk it has been established that a ramdisk size higher than ~10 MB could not be executed on the iDevice, unfortunately a ramdisk containing a SSH server cannot handle such a limited size. The solution was in fact, to alter a bit in the control transfer header specific to the ramdisk. This solution was established after many days by testing ramdom and various header values. Unfortunately it is still unknown why does this bit value bypass the size limitation.
Two more issues, this time related to limera1n, came to light during the libironha1l development. The first one is that limera1n consists of two elements, the source code and the payload. The limera1n payload is unfortunately not documented and is not open source, but it is easily extractable from Jailbreak tools such as RedSn0w. To extract this payload you need to apply the same reverse process as describer in the USB reverse part of this article. Meaning using Redsn0w in a Windows Virtual Machine on your Linux platform and dump all USB transmissions with Wireshark in Man In The Middle. Once the payload dumped, it has been tested and once again came another problem.
The limera1n exploit is based on the principal buffer overflow vulnerability of the bootrom, but unfortunately a USB control command must be sent to the iDevice during the injection process of the payload, so that the payload can be executed. If the control command reaches the iDevice too late, the payload is not executed. Le biggest problem is that generally the USB commands cannot overlap with one another with libusb, and this it is not possible to send the specific USB control command without interrupting the previous injection. The trick and the solution is to play with reception timeouts (acknowledgment replies), the payload is sent to the iDevice with a big timeout and due to its big size the iDevice will take a certain amount of time to deal with it. During this short amount of time (1 to 10 milliseconds), the control command that executes the payload must be sent, this time with a timeout lower than 10 milliseconds to match the iDevice process timing (ideally 1 millisecond).
Here is the prototype of ironha1l:
usage: ./ironha1l -h (help)
[-v verbose_level{0,1,2,3}] [-d libusb_debug_level{0,1,2,3}]
[-l limera1n_file] [-i iBSS_file] [-b iBEC_file]
[-t DeviceTree_file] [-r Ramdisk_file] [-k KernelCache_file]
[-c iBSS_command]
[-z idBus]
Once our tool working and injecting correctly all elements of our customized boot chain, the iDevice boots on our ramdisk containing a SSH server. Meanwhile, on the client side we need to find a way to connect to this SSH server via USB. Fortunately this task is not a real big deal. The MobileDevice framework of Apple (included in iTunes for Windows) contains a daemon called usbmuxd. This daemon is typically what we need as it creates a TCP tunnel over USB to communicate with the iDevice services (in our case the ssh server). Of course, the usbmuxd used by Apple is not open source, but a bunch of great developers have created a usbmuxd version open source that comes with iproxy which is used for port forwarding. So combining usbmuxd with iproxy creates a local port that communicate through USB directly with the SSH socket in listening mode on the iDevice. It was not a big deal to port usbmuxd and iproxy for Android, as these tools are working under Linux. It should also be noted that this open source project is not maintained by Apple, thus each time a new device comes out usbmuxd must be updated by developers and apparently this is not an easy task. In our case our targeted iDevices are all working and supported by the latest version of usbmuxd.
The application portability is a very important aspect, it has been decided to directly integrate libusb and usbmuxd in ironha1l. Before compiling, a script downloads, patches and configures the latest libusb and usbmuxd version. The ironha1l tool suite is compatible with Linux, UNIX, BSD, Mac OS and Android.
Android port and GUI application DFOwn
Since the ICS version, Android supports USB host, which allows to connect to the USB port a USB device such as USB storage, mouse, etc. using a micro USB to USB host adaptor.
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The first thing to do with Android was to root the OS, which is the easiest hacking task ever. The second step was to make sure DFU mode is well detected by Android. For this task either we can use lsusb ported on Android using Android SDK, or we can also use the devices tool contained in the ironha1l tool suite. The USB enumeration has been made on two devices, a SAMSUNG Galaxy SII and a SAMSUNG Galaxy Nexus, both under Android 4.0.3. It appeared that the Galaxy SII could not detect any iDevice in DFU mode (other modes were successfully detected). Even after multiple testings using different USB devices, even with a self-powered USB HUB the problem was still there and was not identified. Fortunately the Galaxy Nexus was working perfectly well under Android 4.0.3. Thus for the next part of the development this smartphone was used.
Android is a Linux based operating system, the compilation of ironha1l tool suite with Android SDK was almost instantaneous. There was only some very basic problems such as the creation of specific Makefiles for Android. The ironha1l binaries were thus sent to the Galaxy Nexus device to be used later with the JAVA GUI application DFOwn. The tools ironha1l, usbmuxd and iproxy have been manually tested and were working perfectly well. The custom boot chain was injected and the Android device can communicate with the SSH server of the Android loaded ramdisk. The iDevice partitions were accessible after mounting in read and/or write, it is thus possible to alter or download files from them directly from our Android smartphone. As described previously, some files such as email database are encrypted and cannot be decrypted without knowing the iDevice passcode, which is not the case for pictures and movies for example, or text message database and contact database.
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The DFOwn JAVA application was created to provide a easy and fast way to use ironha1l and pwn (understand limera1n exploit + custom boot chain injection) the attached iDevice in DFU mode. DFOwn does not currently integrate a SFTP client which thus require the user to use its own SFTP client such as AndFTP to access the iDevice data.
Conclusion
DFOwn and ironha1l are Proof of Concept applications, their goal is to prove an attacker can gain access to your iDevice smartphone files easily with minimal hardware such as an Android smartphone. DFOwn takes about 1 minute to complete the ironha1l boot process on an iDevice. The application is fast, quiet and easy to use. Transfers can go up to 1.5 Mo/s depending of the iDevice and Android device used, which allows the attacker to get a large amount of files very quickly.
Sources Available HERE!
References
- http://images.apple.com/ipad/business/docs/iOS_Security_May12.pdf – iOS Security, Apple
- https://code.google.com/p/iphone-dataprotection – iPhone-dataprotection Sogeti ESEC
- http://theiphonewiki.com/wiki/index.php?title=Grabbing_IMG3_Keys – Jailbreak Community Wiki, Grabbing IMG3 Keys
- http://theiphonewiki.com/wiki/index.php?title=Let%27s_Get_Them_IMG3_Keys_/_IVs – Jailbreak Community Wiki, Let’s Get Them IMG3 Keys / IVs
- https://github.com/planetbeing/iphonelinux – iphonelinux, open source project of planetbeing (Yiduo David Wang)
- http://theiphonewiki.com/wiki/index.php?title=Baker_8B117_(iPhone_4) – iPhone 4 AES keys, Baker 8B117 (iPhone 4)
- http://theiphonewiki.com/wiki/index.php?title=GID-key – Jailbreak Community Wiki, GID-key
- http://www.usb.org/developers/devclass_docs/usbdfu10.pdf – Universal Serial Bus Device Class Specification for Device Firmware Upgrade
- http://theiphonewiki.com/wiki/index.php?title=Limera1n_Exploit – limera1n exploit source code by George Hotz
- http://cgit.sukimashita.com/usbmuxd.git – usbmuxd Linux source code
- http://android.serverbox.ch/?p=151 – Porting Libusb for Android on the Beagleboard in 5 steps
- http://news.softpedia.com/newsImage/Clean-iPhones-Also-Vulnerable-to-Attacks-Developer-Shows-2.jpg – SpyPhone application by Nicolas SERIOT
- http://www.lysesoft.com/products/andftp – AndFTP, a FTP, SFTP, SCP, FTPS client for Android devices
- Book – iOS Hacker’s Handbook by Charlie Miller, Dion Blazakis, Dino Dai Zovi, Stefan Esser, Vincenzo Iozzo, Ralf-Phillip Weinmann
- https://media.blackhat.com/bh-us-11/Esser/BH_US_11_Esser_Exploiting_The_iOS_Kernel_Slides.pdf – iOS Kernel Exploitation, by Stefan Esser
- http://antid0te.com/CSW2012_StefanEsser_iOS5_An_Exploitation_Nightmare_FINAL.pdf – iOS 5 An Exploitation Nightmare?, by Stefan Esser
