Year: 2015

RESEARCH | December 17, 2015

(In)secure iOS Mobile Banking Apps – 2015 Edition

By Ariel Sanchez
Two years ago, I decided to conduct research in order to obtain a global view of the state of security of mobile banking apps from some important banks. In this blog post, I will present my latest results to show how the security of the same mobile banking apps has evolved.

(more…)

RESEARCH | December 9, 2015

Maritime Security: Hacking into a Voyage Data Recorder (VDR)

By Ruben Santamarta
In 2014, IOActive disclosed a series of attacks that affect multiple SATCOM devices, some of which are commonly deployed on vessels. Although there is no doubt that maritime assets are valuable targets, we cannot limit the attack surface to those communication devices that vessels, or even large cruise ships, are usually equipped with. In response to this situation, IOActive provides services to evaluate the security posture of the systems and devices that make up the modern integrated bridges and engine rooms found on cargo vessels and cruise ships. [1]

 

There are multiple facilities, devices, and systems located on ports and vessels and in the maritime domain in general, which are crucial to maintaining safe and secure operations across multiple sectors and nations.

 

Port security refers to protecting all of these assets from acts of piracy, terrorism, and other unlawful activities, such as smuggling. Recent activity appears to demonstrate that cyberattacks against this sector may have been underestimated. As threats evolve, procedures and policies must improve to take these new attack scenarios into account. For example,https://www.federalregister.gov/articles/2014/12/18/2014-29658/guidance-on-maritime-cybersecurity-standards

 

This blog post describes IOActive’s research related to one type of equipment usually present in vessels, Voyage Data Recorders (VDRs). In order to understand a little bit more about these devices, I’ll detail some of the internals and vulnerabilities found in one of these devices, the Furuno VR-3000.

 

What is a Voyage Data Recorder?

(http://www.imo.org/en/OurWork/Safety/Navigation/Pages/VDR.aspx ) A VDR is equivalent to an aircraft’s ‘BlackBox’. These devices record crucial data, such as radar images, position, speed, audio in the bridge, etc. This data can be used to understand the root cause of an accident.

 

Real Incidents

Several years ago, piracy acts were on the rise. Multiple cases were reported almost every day. As a result, nation-states along with fishing and shipping companies decided to protect their fleet, either by sending in the military or hiring private physical security companies.

On February 15, 2012, two Indian fishermen were shot by Italian marines onboard the Enrica merchant vessel, who supposedly opened fire thinking they were being attacked by pirates. This incident caused a serious diplomatic conflict between Italy and India, which continues to the present. https://en.wikipedia.org/wiki/Enrica_Lexie_case

 

‘Mysteriously’, the data collected from the sensors and voice recordings stored in the VDR during the hours of the incident was corrupted, making it totally unusable for authorities to use during their investigation.  As this story, from Indian Times, mentions the VDR could have provided authorities with crucial clues to figure out what really happened.

 

Curiously, Furuno was the manufacturer of the VDR that was corrupted in this incident. This Kerala High Court’s document covers this fact: http://indiankanoon.org/doc/187144571/ However, we cannot say whether the model Enrica Lexie was equipped with was the VR-3000. Just as a side note, the vessel was built in 2008 and the Furuno VR-3000 was apparently released in 2007.

 

Just a few weeks later, on March 1, 2012, the Singapore-flagged cargo ship MV. Prabhu Daya was involved in a hit-and-run incident off the Kerala Coast. As a result, three fishermen were killed and one more disappeared and was eventually rescued by a fishing vessel in the area. Indian authorities initiated an investigation of the accident that led to the arrest of the MV. Prabhu Daya’s captain.

During that process, an interesting detail was reported in several Indian newspapers.

http://www.thehindu.com/news/national/tamil-nadu/voyage-data-recorder-of-prabhu-daya-may-have-been-tampered-with/article2982183.ece

 

So, What’s Going on Here?

From a security perspective, it seems clear VDRs pose a really interesting target. If you either want to spy on a vessel’s activities or destroy sensitive data that may put your crew in a difficult position, VDRs are the key.

 

Understanding a VDR’s internals can provide authorities, or third-parties, with valuable information when performing forensics investigations. However, the ability to precisely alter data can also enable anti-forensics attacks, as described in the real incident previously mentioned.

 

As usual, I didn’t have access to the hardware; but fortunately, I played some tricks and found both firmware and software for the target VDR. The details presented below are exclusively based on static analysis and user-mode QEMU emulation (already explained in a previous blog post). [2]
 
Figure: Typical architecture of a VR-3000

 

Basically, inside the Data Collecting Unit (DCU) is a Linux machine with multiple communication interfaces, such as USB, IEEE1394, and LAN. Also inside the DCU, is a backup HDD that partially replicates the data stored on the Data Recording Unit (DRU). The DRU is protected against aggressions in order to survive in the case of an accident. It also contains a Flash disk to store data for a 12 hour period. This unit stores all essential navigation and status data such bridge conversations, VHF communications, and radar images.

 

The International Maritime Organization (IMO) recommends that all VDR and S-VDR systems installed on or after 1 July 2006 be supplied with an accessible means for extracting the stored data from the VDR or S-VDR to a laptop computer. Manufacturers are required to provide software for extracting data, instructions for extracting data, and cables for connecting between a recording device and computer.

 

The following documents provide more detailed information:
After spending some hours reversing the different binaries, it was clear that security is not one of its main strengths of this equipment. Multiple services are prone to buffer overflows and command injection vulnerabilities. The mechanism to update firmware is flawed. Encryption is weak. Basically, almost the entire design should be considered insecure.
 

Take this function, extracted from from the Playback software, as an example of how not to perform authentication. For those who are wondering what ‘Encryptor’ is, just a word: Scytale.

 

Digging further into the binary services we can find a vulnerability that allows unauthenticated attackers with remote access to the VR-3000 to execute arbitrary commands with root privileges. This can be used to fully compromise the device. As a result, remote attackers are able to access, modify, or erase data stored on the VDR, including voice conversations, radar images, and navigation data.

VR-3000’s firmware can be updated with the help of Windows software known as ‘VDR Maintenance Viewer’ (client-side), which is proprietary Furuno software.

 

The VR-3000 firmware (server-side) contains a binary that implements part of the firmware update logic: ‘moduleserv’

 

This service listens on 10110/TCP.

 

Internally, both server (DCU) and client-side (VDR Maintenance Viewer, LivePlayer, etc.) use a proprietary session-oriented, binary protocol. Basically, each packet may contain a chain of ‘data units’, which, according to their type, will contain different kinds of data.

 

Figure: Some of the supported commands
‘moduleserv’ several control messages intended to control the firmware upgrade process. Let’s analyze how it handles a ‘SOFTWARE_BACKUP_START’ request:
An attacker-controlled string is used to build a command that will be executed without being properly sanitized. Therefore, this vulnerability allows remote unauthenticated attackers to execute arbitrary commands with root privileges.
Figure: ‘Moduleserv’ v2.54 packet processing
Figure: ‘Moduleserv’ v2.54 unsanitized system call

 

At this point, attackers could modify arbitrary data stored on the DCU in order to, for example, delete certain conversations from the bridge, delete radar images, or alter speed or position readings. Malicious actors could also use the VDR to spy on a vessel’s crew as VDRs are directly connected to microphones located, at a minimum, in the bridge.

 

However, compromising the DCU is not enough to cover an attacker’s tracks, as it only contains a backup HDD, which is not designed to survive extreme conditions. The key device in this anti-forensics scenario would be the DRU. The privileged position gained by compromising the DCU would allow attackers to modify/delete data in the DRU too, as this unit is directly connected through an IEEE1394 interface. The image below shows the structure of the DRU.
Figure: Internal structure of the DRU

Before IMO’s resolution MSC.233(90) [3], VDRs did not have to comply with security standards to prevent data tampering. Taking into account that we have demonstrated these devices can be successfully attacked, any data collected from them should be carefully evaluated and verified to detect signs of potential tampering.

 

IOActive, following our responsible disclosure policy, notified the CERT/CC about this vulnerability in October 2014. The CERT/CC, working alongside the JPCERT/CC, were in contact with Furuno and were able to reproduce and verify the vulnerability. Furuno committed to providing a patch for their customers “sometime in the year of 2015.” IOActive does not have further details on whether a patch has been made available.
 
References
————–

RESEARCH | November 25, 2015

Privilege Escalation Vulnerabilities Found in Lenovo System Update

By Sofiane Talmat
Lenovo released a new version of the Lenovo System Update advisory (https://support.lenovo.com/ar/es/product_security/lsu_privilege) about two new privilege escalation vulnerabilities I had reported to Lenovo a couple of weeks ago (CVE-2015-8109, CVE-2015-8110). IOActive and Lenovo have issued advisories on these issues.
 

Before digging into the details, let’s go over a high-level overview of how the Lenovo System Update pops up the GUI application with Administrator privileges.
 
Here is a discussion of the steps depicted above:


1 – The user starts System Update by running the tvsu.exe binary which runs the TvsuCommandLauncher.exe with a specific argument. Previously, Lenovo fixed vulnerabilities that IOActive discovered where an attacker could impersonate a legitimate caller and pass the command to be executed to the SUService service through named pipes to gain a privilege escalation. In the newer version, the argument is a number within the range 1-6 that defines a set of tasks within the dll TvsuServiceCommon.dll

 

2 – TvsuCommandLauncher.exe then, as usual, contacts the SUService service that is running with System privileges, to process the required query with higher privileges.

 

3 – The SUService service then launches the UACSdk.exe binary with System privileges to prepare to execute the binary and run the GUI interface with Administrator privileges.

 

4 – UACSdk.exe checks if the user is a normal unprivileged user or a Vista Administrator with the ability to elevate privileges.

 

5 – Depending on user privileges:

 

    • For a Vista Admin user, the user’s privileges are elevated.
    • For an unprivileged user, UACSdk.exe creates a temporary Administrator account with a random password which is deleted it once the application is closed.

The username for the temporary Administrator account follows the pattern tvsu_tmp_xxxxxXXXXX, where each lowercase x is a randomly generated lower case letter and each uppercase X is a randomly generated uppercase letter. A 19-byte, random password is generated.


Here is a sample of a randomly created user:    



6 – Through tvsukernel.exe binary, the main Lenovo System Update GUI application is then run with Administrator privileges. 




BUG 1 : Lenovo System Update Help Topics Privilege Escalation
The first vulnerability is within the Help system and has two entry points by which a user can open an online help topic that starts an instance of Internet Explorer.

1 – The link in the main application interface 

 
 

2 – By clicking on the Help icon at top right and then clicking Settings
 

 

 

 
Since the main application Tvsukernel.exe is running as Administrator, the web browser instance that starts to open a Help URL inherits the parent Administrator privileges.
From there, an unprivileged attacker has many ways to exploit the web browser instance running under Administrator privileges to elevate his or her own privileges to Administrator or SYSTEM.
BUG 2 : Lenovo System Weak Cryptography Function Privilege Escalation
Through a more technical bug and exploitable vulnerability, the temporary administrator account is created in specific circumstances related to Step 5b in the overview.
The interesting function for setting the temporary account is sub_402190 and contains the following important snippets of code:
 
 
The function sub_401810 accepts three arguments and is responsible for generating a random string pattern with the third argument length.
 
Since sub_401810 generates a pattern using RAND, the initialization of the seed is based on the addition of current time and rand values and defined as follows:
 
 
 
Once the seed is defined, the function generates the random value using a loop with RAND and division/multiplication with specific values.
 
Rather than posting the full code, I’ll note that a portion of those loops looks like the following:
 
 
 
The first call to this function is used to generate the 10-letter suffix for the Administrator username that will be created as “tvsu_tmp_xxxxxXXXXX”
 
Since it is based on rand, the algorithm is actually predictable. It is possible for an attacker to regenerate the same username based on the time the account was created.
 
To generate the password (which is more critical), Lenovo has a more secure method: Microsoft Crypto API (Method #1) within the function sub_401BE0. We will not dig into this method, because the vulnerability IOActive discovered is not within this function. Instead, let’s look at how Method #2 generates a password, if Method #1 fails.
 
Let’s return to the snippets of code related to password generation:
 
 
 
We can clearly see that if function sub_401BE0 fails, the execution flow fails back using the custom RAND-based algorithm (defined earlier in function sub_401810) to generate a predictable password for the temporary Administrator account. In other words, an attacker could predict the password created by Method #2.
 

This means an attacker could under certain circumstances predict both the username and password and use them to elevate his or her privileges to Administrator on the machine.
RESEARCH | November 19, 2015

Breaking into and Reverse Engineering iOS Photo Vaults

By Michael Allen

Every so often we hear stories of people losing their mobile phones, often with sensitive photos on them. Additionally, people may lend their phones to friends only to have those friends start going through their photos. For whatever reason, a lot of people store risqué pictures on their devices. Why they feel the need to do that is left for another discussion. This behavior has fueled a desire to protect photos on mobile devices.

One popular option are photo vault applications. These applications claim to protect your photos, videos, etc. In general, they create albums within their application containers and limit access with a passcode, pattern, or, in the case of newer devices, TouchID.

I decided to take a look at some options for the iOS platform. I did a quick Google search for “best photo vaults iOS” and got the following results:
 
Figure 1: Search results for best iOS photo vaults


I downloaded the free applications, as this is what most typical users would do. This blog post discusses my findings.
Lab Setup
  • Jailbroken iPhone 4S (7.1.2)
  • BurpSuite Pro
  • Hex editor of choice
  • Cycript

Applications Reviewed
  • Private Photo Vault
  •  Photo+Video Vault Keep Safe(My Media)
  •  KeepSafe

I will cover the common techniques I used during each iOS application assessment. Additionally, I will take a deeper look at the Private Photo Vault application and get into some actual reverse engineering. The techniques discussed in the reverse engineering section can be applied to the other applications (left as an exercise for the reader).
Note: Unless otherwise stated, all commands are issued from Mac OS after having ssh’d into the jailbroken mobile device.
 
Private Photo Vault
The first application I looked at was Private Photo Vault. As it turns out, there have been several write-ups about the security, or lack thereof, of this application (see the references section for additional details). Because those write ups were published some time ago, I wanted to see if the developers had corrected the issues. As it turns out, the app was still vulnerable to some of the issues at the time of writing this post.
Bypassing the Lock Screen
When the app launches, the user is presented with the following screen:
Figure 2: Private Photo Vault Lock Screen
 
Bypassing this lock screen was trivial. The first step is to identify the Photo Vault process and then attach to it with cycript. For those not familiar with cycript, the following is taken from the cycript.org site:
“Cycript allows developers to explore and modify running applications on either iOS or Mac OS X using a hybrid of Objective-C++ and JavaScript syntax through an interactive console that features syntax highlighting and tab completion.”
To identify the Photo Vault process we issue the following commands:
ps –e | grep “Photo”
And then attach to it as shown:
cycript –p PhotoVault
 
 
 
Figure 3: Attaching to PhotoVault process with cycript
We then print the current view hierarchy using recursiveDescription by issuing the following command:
[[UIApp keyWindow] recursiveDescription]
 
 
 
Figure 4: Current View Hierarchy with recursiveDescription
 
Reviewing the current view hierarchy, we see a number of references to PasswordBox. Let’s see if we can alter what is being displayed. To do that we can issue the following command:
[#viewAddress setHidden:YES].
In this case we are testing the first PasswordBox at 0x15f687f0.
Figure 5: Hiding the first password input box
 
After executing the command we note that the first PasswordBox disappeared:
Figure 6: First password box hidden
Great, we can alter what is being displayed. Having obtained the current view, we now need to determine the controller. This can be accomplished with nextResponder as shown below. See references for details on nextResponder and the whole MVC model.
In a nutshell we keep calling nextResponder on the view until we hit a controller. In our case, we start with [#0x15f687f0 nextResponder] which returns <UIView: 0x15f68790> and then we call nextResponder on that like [#0x15f68790 nextResponder]. Eventually we hit a controller as shown:
Figure 7: Determining the View Controller
 
The WhiteLockScreenViewController controller seems to be responsible for the view. Earlier I dumped the class information with class-dump-z (not shown here). Examining the class revealed an interesting method called dismissLockScreen. Could it be that easy? As it turned out, it was. Simply calling the method as shown below was enough to bypass the lock screen:
Figure 8: Bypassing the lock screen with dismissLockScreen
 
Insecure Storage
During the setup I entered a passcode of 1337 to “protect” my photos. The next step, therefore, was to determine how the application was storing this passcode. Browsing the application directory revealed that the passcode was being stored in plaintext in the com.enchantedcloud.photovault.plistfile in /var/mobile/Applications/A025EF5F-ED84-4D82-A23D-BBCFE183F539/Library/Preferences.
As a side note I wonder what would be the effect of changing “Request Pin = 0”? It may be worth investigating further.
Figure 9: Passcode stored in plaintext
 
Not only is the PIN stored in plaintext, but the user has the option to password protect their albums. This again is stored in plaintext in the Albums.plist plist file.
Figure 10: Album password stored in plaintext
No Encryption
As if this wasn’t bad enough, the stored photos were not encrypted. This has already been pointed out elsewhere. Surprisingly enough, it remains the case as at the time of this writing. The pictures are stored in the /0 directory:
Figure 11: Location of unencrypted photos
 
 
 
Figure 12: Unencrypted view of stored photo
Reverse Engineering Private Photo Vault
Ok, so we have seen how to bypass the lock screen using cycript. However, let’s say that you wanted to go “under the hood “in order to achieve the same goal.
You could achieve this using:
  • IDA Pro/Hopper
  • LLDB
  • Usbmuxd
  • Debugserver

Environment Setup
Attach the mobile device to your host machine and launch tcprelay (usbmuxd directory) using the following syntax:
tcprelay.py  -t  <remote-port-to-forward><local-port-to-listen>
 
 
 
Figure 13: Launching tcprelay for debugging via USB
Tcprelay allows us to debug the application over USB as opposed to wifi, which can often be slow.
SSH into the device, start the debugserver, and attach to the PhotoVault process. Issue the following command:
debugserver *:8080 –a “PhoyoVault”
 
 
 
Figure 14: Launching debugserver on the mobile device
 
Launch lldb from your host machine, and connect to the listening debug server on the mobile device by issuing the following command from within lldb:
process connect connect://localhost:8080
 
 
 
Figure 15: Connecting to debugserver with lldb
Decrypt Binary
Now that the environment is configured, we can start debugging. Decrypt the binary and open it in IDA. I used the following command to decrypt the binary:
DYLD_INSERT_LIBRARIES=dumpdecrypted_armv7.dylib /var/mobile/Applications/A025EF5F-ED84-4D82-A23D-BBCFE183F539/PhotoVault.app/PhotoVault mach -o decryption dumper
 
 
 
Figure 16:Decrypting the PhotoVault binary
At this point I usually check to see if the binary is a FAT binary (i.e. it supports many devices). The command for that is: otool –hV PhotoVault.decrypted
 
 
 
Figure 17: Determining if the binary is a FAT binary
 
If it is indeed a FAT binary, I strip the architecture for my device. Given I am running an iPhone 4S, I ran the following command:
lipo -thin armv7 -output PhotoVault-v7 PhotoVault.decrypted.
The PhotoVault-v7 binary is what we will analyze in IDA or Hopper (see the reference section for instructions on configuring lldb and debugserver).
Earlier we established that WhiteLockScreenViewController was the controller responsible for the lock screen. This will become important in a bit. If we enter an incorrect password, the application prints “Wrong Passcode – Try Again”. Our first step, therefore, is to find occurrences of this in IDA.

Figure 18: Searching for occurrences of “Wrong Passcode”
We see several occurrences, but any reference to WhiteLockScreenViewController should be of interest to us. Let’s investigate this more. After a brief examination we discover the following:

Figure 19: Examining WhiteLockScreenViewController customKeyboardButtonPressed
 
At 0013A102, the lockScreen:isPasswordCorrect method is called, and at 0013A114 the return value is checked. At 0013A118 a decision is made on how to proceed. If we entered an incorrect passcode, the application will branch to loc_13A146 and display “Wrong Passcode” as shown in the snippet below. 
Figure 20: Wrong Passcode branch we need to avoid
Obviously, we want the application to branch to 0013A11A, because in that branch we see references to a selRef_lockScreen_didEnterCorrectPassword_ method.
Figure 21: Branch we are interested in taking
Let’s set breakpoint at 0013A110, right before the check for the return value is done. Before we can do that, we need to account for ASLR, so we must first determine the ASLR Offset on the device.
Figure 22: Breakpoint will set at 0013A110
To accomplish this we issue the following command from within our lldb session:
image list –o -f
The image is loaded at 0xef000 so the address we need to break on is the 0x000ef000 + 0013A110.
Figure 23: Determining ASLR offset
We set a breakpoint at 0x229110 with the following command: br s -a 0x229110.
From this point breakpoints will be calculated as ASLR Offset + IDA Offset.
 
Figure 24: Setting the breakpoint
With our breakpoint set, we go back to the device and enter an arbitrary passcode. The breakpoint is hit and we print the value of register r8 with p $r8.
 
 
 
Figure 25: Examining the value in register r8
Given the value of zero, the TST.W R8, #0xFF instructions will see us taking the branch that prints “Wrong Passcode”. We need to change this value so that we take the other branch. To do that we issue the following command: register write r8 1
 
 
 
Figure 26: Updating the r8 register to 1
 
The command sets the value of register r8 to 1. We are almost there. But before we continue, let’s examine the branch we have taken. In that branch we see a call to lockScreen_didEnterCorrectPassword. So again, we search IDA for that function and the results show it references the PasswordManager class.
Figure 27: Searching IDA for occurences of lockScreen_didEnterCorrectPassword
 
We next examine that function where we notice several things happening:
Figure 28: Examining lockScreen_didEnterCorrectPassword
 
In short, in this block the application reads the PIN stored on the device and compares it to the value we entered at 0012D498. Of course this check will fail, because we entered an incorrect PIN. Looking further at this function revealed a call to the familiar dismissLockScreen. Recall this is the function we called in cycript earlier.
Figure 29: Branch with dismissLockScreen
 
It seems then that we need to take this branch. To do that, we change the value in r0  so that we get our desired result when the TST instruction is called. This ends up tricking the application into thinking we entered the correct PIN. We set a breakpoint at 0012D49C (i.e. the point at which we test for the return value from isEqualToString). Recall we are still in the lockScreen_didEnterCorrectPassword method of the PasswordManager class.
Figure 30: Point at which the PIN is verified
We already know the check will fail, since we entered an incorrect PIN, so we update the value in r0 to 1.
Figure 31: Updating r0 register to 1 to call dismissLockScreen
When we do that and continue execution, the dismissLockScreen method is called and the lock screen disappears, granting us access to the photos. So to recap the first patch allows us to call lockScreen_didEnterCorrectPassword. And then the second patch allows us to call dismissLockScreen, all with an arbitrary pin.
Let’s now look at the other applications.
My Media
Insecure Webserver
This was a very popular application in the app store. However, it suffered from some of the same vulnerabilities highlighted previously. What is interesting about this application is that it starts a web server on port 5555, which essentially allows users to manage their albums.
Figure 32: Web server started on port 5555
Browsing to the address results in the following interface:
Figure 33: My Media Wifi Manager
 
The first thing I noticed was that there was no authentication. Anybody on the same network could potentially gain access to the user’s albums. Looking a little deeper revealed that the application was vulnerable to common web application vulnerabilities. An example of this is stored cross-site scripting (XSS) in the Album name parameter:
Figure 34: Stored XSS in Album name
Insecure Storage
Again, the photos were not encrypted (verified using the hex editor from earlier). Photos and videos were stored in the following location:
/var/mobile/Applications/61273D04-3925-41EF-BD63-C2B0BC128F70/Library/XFFile/Decoy/1/Picture/Album1
Figure 35: Insecure storage of photos
On the device, this looks like the following:
Figure 36:Albums and photos on device
 
One of the features of these password-protected photo vaults is the ability to setup decoys. If the user chooses to create a decoy, then when the decoy password is entered it takes them to a “fake” album. I created a decoy in this application and found that the photos were also not encrypted (not that I expected them to be). I created a decoy album and added a photo. The decoy photos were stored in the following location:
/var/mobile/Applications/B73BB177-CEB7-4576-BDFC-2408A0369D42/Library/XFFile/Decoy/2/Picture/Decoy Album
The application stored user credentials in an unencrypted sqlite database. The passcode required to access the application was 1234 and was tied to the administrative account as shown. This was the passcode I chose when I was configuring the application. I also created a decoy user. These credentials were stored plaintext in the users table.
Figure 37: Extracting credentials with sqlite
 
KeepSafe
 
Bypassing the Lock Screen
Again bypassing the lock screen was trivial.
Figure 38: KeepSafe LockScreen
 
The lock screen could be bypassed by calling the showMainStoryboard method from the KeepSafe.AppDelegateclass. Again we attach to the process with cycript and this time we get the instance methods:
Examining the instance methods reveals the following methods:
And calling the showAccountStoryboard or showMainStoryboard methods as shown bypasses the lock screen: 
Figure 39: Bypassing the lock screen
 
The application also allows the user to password protect each album. Each album is synced to the cloud.
Figure 40: KeepSafe cloud storage
I discovered that the password for the albums was returned in plaintext from the server as shown:
Figure 41: Album password return in plaintext from the server
 
An attacker could therefore not only bypass the lockscreen but he could obtain the passcode for password protected albums as well.
Conclusion
Ok so let’s do a quick recap on what we were able to accomplish. We used:
  • cycript to bypass the lock screens
  • sqlite to extract sensitive information from the application databases
  • plutil to read plist files and access sensitive information
  • BurpSuite Pro to intercept traffic from the application
  • IDA Pro to reverse the binary and achieve results similar to cycript

The scary part of this is that, on average, it took less than 30 minutes to gain access to the photos and user credentials for each application. The only exception was the use of IDA, and as we highlighted, we only did that to introduce you to and get you comfortable reading ARM assembly. In other words, it’s possible for an attacker to access your private photos in minutes.
In all cases it was trivial to bypass the lock screen protection. In short I found:
  • No jailbreak detection routines
  • Insecure storage of credentials
  • Photos stored unencrypted
  • Lock screens are easy to bypass
  • Common web application vulnerabilities

Let me hasten to say that this research does not speak to ALL photo vault applications. I just grabbed what seemed to be the most popular and had a quick look. That said, I wouldn’t be surprised if others had similar issues, as developers often make incorrect assumptions (believing users will never have access to the file system).
What are some of the risks? First and foremost, if you are running these apps on a jailbroken device, it is trivial to gain access to them. And in the case of My Media, even if you are not on a jailbroken device, anyone could connect to the media server it starts up and access your data.
More importantly though is the fact that your data is not encrypted. A malicious app (some of which have popped up recently) could gain access to your data.
The next time you download one of these apps, keep in mind it may not be doing what you think it is doing. Better yet, don’t store “private” photos on your device in the first place.
References:
  1. http://www.zdziarski.com/blog/?p=3951
  2. Hacking and Securing iOS Applications: Stealing Data, Hijacking Software, and How to Prevent It
  3. http://www.cycript.org/
  4. http://cgit.sukimashita.com/usbmuxd.git/snapshot/usbmuxd-1.0.8.tar.gz
  5. http://resources.infosecinstitute.com/ios-application-security-part-42-lldb-usage-continued/
  6. https://github.com/stefanesser/dumpdecrypted
  7. https://developer.apple.com/library/ios/technotes/tn2239/_index.html#//apple_ref/doc/uid/DTS40010638-CH1-SUBSECTION34
  8. https://developer.apple.com/library/ios/documentation/UIKit/Reference/UIResponder_Class/#//apple_ref/occ/instm/UIResponder/nextResponder

ADVISORIES |

Lenovo TVSUkernel Escalation of Privileges

By Sofiane Talmat

The Lenovo System Update allows least-privileged users to perform system updates. To do this, System Update includes the System Update service (SUService.exe). This service runs as the privileged SYSTEM user, creates a temporary user account with Administrator privileges, and starts a GUI application (Tvsukernel.exe) with the new Administrator account. Once the application is closed, the temporary Administrator account is appropriately deleted. However the GUI application contains links to online support and privacy help topics, which, when clicked, start a web browser instance under the temporary Administrator account to display the online topic.

As a result, an attacker who is unprivileged can exploit the web browser instance that is running as Administrator to elevate his or her own privileges to Administrator or SYSTEM. (more…)

ADVISORIES |

Lenovo System Update Created an Insecure Random Administrator Password

By Sofiane Talmat

This vulnerability allows a local unprivileged user to elevate privileges to Administrator or SYSTEM. Since the user is running the System Update is an unprivileged user, the SUService that is running as System will run the UACsdk.exe binary to create a temporary Administrator account to run the GUI application (Tvsukernel.exe). (more…)

EDITORIAL | October 16, 2015

Five Reasons Why You Should Go To BruCON

By Alejandro Hernandez

BruCON is one of the most important security conferences in Europe. Held each October, the ‘Bru’ in ‘BruCON’ refers to Brussels, the capital of Belgium, where it all started. Nowadays, it’s held in the beautiful city of Ghent, just 55 mins from its origin. I had the chance to attend this year, and here are the five things that make it a great conference, in my opinion.

You can check out BruCON’s promo video here: https://www.youtube.com/watch?v=ySmCRemtMc4.
1. The conference
Great talks presented by international speakers; from deeply technical talks, to threat intelligence and other high-level stuff. You might run into people and friends from Vegas or another security conference.
A circular and well illuminated stage. You better not be caught taking a nap, unless you want a picture of yourself sleeping on the Internet.

(Shyama Rose talking about BASE jumping and risk)

While paid trainings take place two or three days before the conference, free workshops are available to the public during the two-day conference.

(Beau Woods (@beauwoods) giving a cool workshop named:

«Escalating Privileges Through Better Communication»)

While at BruCON, I presented my research on security deficiencies in electroencephalography (EEG) technologies. EEG is a non-invasive method of recording electrical brain activity (synaptic activity between neurons) taken from the scalp. EEG has increasingly been adopted across different industries, and I showed how the technology is prone to common network and application attacks. I demonstrated brain signal sniffing and data tampering through man-in-the-middle attacks, as well as denial-of-service bugs in EEG servers. Client-side applications that analyze EEG data are also prone to application flaws, and I showed how trivial fuzzing can uncover many of them. You can find the related material here: slides, demos (videos) [resource no longer available], and my live talk (video).
2. The city
The medieval architecture in Ghent will enchant you. It’s a really cool city, everywhere you look. Full of restaurants, cafes, and of course, pubs. Students from all ages also make this city full of vibe. You can easily spend two more days and enjoy all Ghent has to offer.
All of this is just around the corner from the venue.
3. The b33r
I’m not a b33r connoisseur, but most of the beers I tasted while in Ghent were, according to my taste, really good. Belgium is catalogued as one of the best beer countries in the world, which speaks for itself. In a nice gesture by the conference organizers, speakers were given a single bottle of a hard-to-find beer, Westvleteren 12, which has been rated as “the best beer in the world.” I have no idea know how they got them, as the brewer does not produce large amounts of this beer and only sells it to a select few people.
Beer at the venue, beer between talks, and there was even a night where we mixed good beer with ice cream. It was interesting.
4. The venue
The conference is held in the heart of the city, near all the hotels, just two or three blocks from where you’re most likely to stay. The organizers thought out every single detail to help you arrive right on time at the venue.
The main hall is perfect for networking and serves b33r, coffee, and food all day, not only during specific hours.
A renowned hacker DJ is dropping some bass or a pianist girl (computer scientist who wrote code for Google) took turns to make those moments even better.

 

Wouldn’t be a good conference without a Wall of Sheep; it was RickRolled though ;D
(Picture taken by @sehnaoui)
The party venue, just three blocks from the stage, had a good hacker ambience and a good sound atmosphere created by two well-known DJs: @CountNinjula & @KeithMyers.

 

(Picture taken by @wimremes)
5. The old video game consoles
If you’re not interested in a talk, or simply bored, just head upstairs and travel back in time with a whole hall of old consoles. “Here comes a new challenger” are accepted…as long as there’s b33r or money involved.

 

 

 
Well, that’s it, another great security conference for you to consider in the future.
Finally, thanks to all this year’s organizers and volunteers. Perhaps you’ll join in next year 😉

 

(Photo taken by @SenseiZeon)
Cheers!

ADVISORIES | September 28, 2015

Harman-Kardon UConnect Vulnerability

By Chris Valasek & Charlie Miller

UConnect 8.4AN/RA3/RA4 are vehicle-based infotainment systems. UConnect systems are integrated in certain makes of Chrysler, Dodge, Jeep, and Ram vehicles.

The UConnect infotainment system allowed an unauthenticated connection from other access points on the Sprint Network. An attacker could issue commands to other components within the vehicle through the infotainment system. (more…)

RESEARCH | September 22, 2015

Is Stegomalware in Google Play a Real Threat?

By Alfonso Muñoz
For several decades, the science of steganography has been used to hide malicious code (useful in intrusions) or to create covert channels (useful in information leakage). Nowadays, steganography can be applied to almost any logical/physical medium (format files, images, audio, video, text, protocols, programming languages, file systems, BIOS, etc.). If the steganographic algorithms are well designed, the hidden information is really difficult to detect. Detecting hidden information, malicious or not, is so complex that the study of steganalytic algorithms (detection) has been growing. You can see the growth in scientific publications (source: Scholar Google) and research investment by governments or institutions.
In fact, since the attacks on September 11, 2001, there has been a lot of discussion on the possibility of terrorists using this technology. See:
 
 
 
 
In this post, I would like to illustrate steganography’s ability to hide data in Android applications. In this experiment, I focus on Android applications published in Google Play, leaving aside alternative markets with lower security measures, where it is easier to introduce malicious code.
 
 
Is it possible to hide information on Google Play or in the Android apps released in it?
 
The answer is easy: YES! Simple techniques have been documented, from hiding malware by renaming the file extension (Android / tr DroidCoupon.A – 2011, Android / tr SmsZombie.A – 2012, Android / tr Gamex.A – 2013) to more sophisticated procedures (AngeCryption – BlackHat Europe October2014).
 
Let me show some examples in more depth:
 
 
Google Play Web (https://play.google.com)
 
Google Play includes a webpage for each app with information such as a title, images, and a text description. Each piece of information could conceal data using steganography (linguistic steganography, image steganography, etc.). In fact, I am going to “work” with digital images and demonstrate how Google “works” when there is hidden information inside of files.
 
To do this, I will use two known steganographic techniques: adding information to the end of file (EOF) and hiding information in the least significant bit (LSB) of each pixel of the image.
–      
 
          PNG Images
 
You can upload PNG images to play.google.com that hide information using EOF or LSB techniques. Google does not remove this information.
 
For example, I created a sample app (automatically generated – https://play.google.com/store/apps/details?id=com.wMyfirstbaskeballgame) and uploaded several images (which you can see on the web) with hidden messages. In one case, I used the OpenStego steganographic tool (http://www.openstego.com/) and in another, I added the information at the end of an image with a hex editor.
 
The results can be seen by performing the following steps (analyzing the current images “released” on the website):
Example 1: PNG with EOF
 
 
Step 2: Loot at the end of the file 🙂
Example 2: PNG with LSB
 
 
Step 2: Recover the hidden information using Openstego (key=alfonso)
 
JPEG Images
If you try to upload a steganographic JPEG image (EOF or LSB) to Google Play, the hidden information will be removed. Google reprocesses the image before publishing it. This does not necessarily mean that it is not possible to hide information in this format. In fact, in social networks such as Facebook, we can “avoid” a similar problem with Secret Book or similar browser extensions. I’m working on it…
 
https://chrome.google.com/webstore/detail/secretbook/plglafijddgpenmohgiemalpcfgjjbph?hl=en-GB
 
In summary, based on the previous proofs, I can say that Google Play allows information to be hidden in the images of each app. Is this useful? It could be used to exchange hidden information (covert channel using the Google Play). The main question is whether an attacker could use information masked for some evil purpose. Perhaps they could use images to encode executable code that “will exploit” when you are visiting the web (using for example polyglots + stego exploits) or another idea. Time will tell…
 
 
 
APK Steganography
 
Applications uploaded toGoogle Play are not modified by the market. That is, an attacker can use any of the existing resources in an APK to hide information, and Google does not remove that information. For example, machine code (DEX), PNG, JPEG, XML, and so on.
 
 
Could it be useful to hide information on those resources?
 
An attacker might want to conceal malicious code on these resources and hinder automatic detection (static and dynamic analysis) that focuses on the code (DEX). A simple example would be an application that hides a specific phone number in an image (APT?).
 
The app verifies the phone number, and after a few clicks in a specific screen on a mobile phone, checks if the number is equal to that stored in the picture. If the numbers match, you can start leaking information (depending on the permissions allowed in the application).
 
I want to demonstrate the potential of Android stegomalware with a PoC. Instead of developing it, I will analyze an active sample that has been on Google Play since June 9, 2014. This stegomalware was developed by researchers at Universidad Carlos III de Madrid, Spain (http://www.uc3m.es). This PoC hides a DEX file (executable code) in an image (resource) of the main app. When the app is running, and the user performs a series of actions, the image recovers the “new” DEX file. This code runs and connects to a URL with a payload (in this case harmless). The “bad” behavior of this application can only be detected if we analyze the resources of the app in detail or simulate the interaction the app used for triggering the connection to the URL.
 
Let me show how this app works (static manual analysis):
Step 1: Download the APK to our local store. This requires a tool, such as an APK downloader extension or a specific web as http://apps.evozi.com/apk-downloader/
Step 2. Unzip the APK (es.uc3m.cosec.likeimage.apk)
Step 3. Using the Stegdetect steganalytic tool (https://github.com/abeluck/stegdetect) we can detect hidden information in the image “likeimage.jpg”. The author used the F5 steganographic tool (https://code.google.com/p/f5-steganography/).
 
es.uc3m.cosec.likeimageresdrawable-hdpilikeimage.jpg
likeimage.jpg : f5(***)
Step 4. To analyze (reverse engineer) what the app is doing with this image, I use the dex2jar and jd tools.
Step 5. Analyzing the code, we can observe the key used to hide information in the image. We can recover the hidden content to a file (bicho.dex).
java -jar f5.jar x -p cosec -e bicho.dex likeimage.jpg
 
Step 6. Analyzing the new file (bicho.dex), we can observe the connection to http://cosec-uc3m.appspot.com/likeimage for downloading a payload.
 
Step 7. Analyzing the code and payload, we can demonstrate that it is inoffensive.
ZGV4CjAzNQDyUt1DKdvkkcxqN4zxwc7ERfT4LxRA695kAgAAcAAAAHhWNBIAAAAAAAAAANwBAAAKAAAAcAAAAAQAAACYAAAAAgAAAKgAAAAAAAAAAAAAAAMAAADAAAAAAQAAANgAAABsAQAA+AAAACgBAAAwAQAAMwEAAD0BAABRAQAAZQEAAKUBAACyAQAAtQEAALsBAAACAAAAAwAAAAQAAAAHAAAAAQAAAAIAAAAAAAAABwAAAAMAAAAAAAAAAAABAAAAAAAAAAAACAAAAAEAAQAAAAAAAAAAAAEAAAABAAAAAAAAAAYAAAAAAAAAywEAAAAAAAABAAEAAQAAAMEBAAAEAAAAcBACAAAADgACAAEAAAAAAMYBAAADAAAAGgAFABEAAAAGPGluaXQ+AAFMAAhMTUNsYXNzOwASTGphdmEvbGFuZy9PYmplY3Q7ABJMamF2YS9sYW5nL1N0cmluZzsAPk1BTElDSU9VUyBQQVlMT0FEIEZST00gVEhFIE5FVDogVGhpcyBpcyBhIHByb29mIG9mIGNvbmNlcHQuLi4gAAtNQ2xhc3MuamF2YQABVgAEZ2V0UAAEdGhpcwACAAcOAAQABw4AAAABAQCBgAT4AQEBkAIAAAALAAAAAAAAAAEAAAAAAAAAAQAAAAoAAABwAAAAAgAAAAQAAACYAAAAAwAAAAIAAACoAAAABQAAAAMAAADAAAAABgAAAAEAAADYAAAAASAAAAIAAAD4AAAAAiAAAAoAAAAoAQAAAyAAAAIAAADBAQAAACAAAAEAAADLAQAAABAAAAEAAADcAQAA
 
The code that runs the payload:
 
Is Google detecting these “stegomalware”?
 
Well, I don’t have the answer. Clearly, steganalysis science has its limitations, but there are other ways to monitor strange behaviors in each app. Does Google do it? It is difficult to know, especially if we focus on “mutant” applications. Mutant applications are applications whose behavior could easily change. Detection would require continuous monitoring by the market. For example, for a few months I have analyzed a special application, including its different versions and the modifications that have been published, to observe if Google does anything with it. I will show the details:
Step 1. The mutant app is “Holy Quran video and MP3” (tr.com.holy.quran.free.apk). Currently at https://play.google.com/store/apps/details?id=tr.com.holy.quran.free

Step 2.  Analyzing the current and previous version of this app, I discover connections to specific URLs (images files). Are these truly images? Not all.

Step 3. Two URLs that the app connects to are very interesting. In fact, they aren’t images but SQLite databases (with messages in Turkish). This is the trivial steganography technique of simply renaming the file extension. The author changed the content of these files:

Step 4. If we analyze these databases, it is possible to find curious messages. For example, recipes with drugs.

Is Google aware of the information exchanged using their applications? This example does not cease to be a mere curiosity, but such procedures might violate the policy of publication of certain applications on the market or more serious things.
 
Figure: Recipes inside the file io.png (SQLite database)

In summary, this small experiment shows that we can hide information on Google Play and Android apps in general. This feature can be used to conceal data or implement specific actions, malicious or not. Only the imagination of an attacker will determine how this feature will be used…


Disclaimer: part of this research is based on a previous research by the author at ElevenPaths
RESEARCH | September 15, 2015

The iOS Get out of Jail Free Card

By Michael Allen
If you have ever been part of a Red Team engagement, you will be familiar with the “Get out of Jail Free Card”. In a nutshell, it’s a signed document giving you permission to perform the activity you were caught doing. In some instances, it’s the difference between walking away and spending the night in a jail cell. You may be saying, “Ok, but what does a Get out of Jail Free Card have to do with iOS applications?”

Well, iOS mobile application assessments usually occur on jailbroken devices, and application developers often implement measures that seek to thwart this activity. The tester often has to come up with clever ways of bypassing detection and breaking free from this restriction, a.k.a. “getting out of jail”. This blog post will walk you through the steps required to identify and bypass frequently recommended detection routines. It is intended for persons who are just getting started in reverse engineering mobile platforms. This is not for the advanced user.

Environment Setup
§  Jailbroken iPhone 4S (iOS 7.xx)
§  Xcode 6.4 (command-line tools)
§  IDA Pro or Hopper
§  Mac OS X
 
Intro to ARM Architecture
Before we get started, let’s cover some very basic groundwork. iOS applications are compiled to native code for the ARM architecture running on your mobile device. The ARM architecture defines sixteen 32-bit general-purpose registers, numbered from R0-R15. The first 12 are for general-purpose usage, and the last three have special meaning. R13 is denoted as the stack pointer (SP), R14 the link register (LR), and R15 the program counter (PC). The link register normally holds the return address during a function call. R0-R3 hold arguments passed to functions with R0 storing the return value. For the purposes of this post, the most important takeaway is that register R0 holds the return value from a function call. See the references section for additional details on the ARM architecture.
Detecting the Jailbreak
When a device is jailbroken, a number of artifacts are often left behind. Typical jailbreak detection routines usually involve checking for those artifacts before allowing access to the application. Some of the checks you will often see include checking for:
  • Known file paths
  • Use of non-default ports such as port 22(OpenSSH), which is often used to connect to and administer the device
  • Symbolic links to various directories (e.g. /Applications, etc.)
  • Integrity of the sandbox (i.e. a call to fork() should return a negative value in a properly functioning sandbox)

In addition to the above, developers will often seek to prevent us from debugging the process with the use of PT_ATTACH_DENY, which prevents the use of the ptrace() system call (a call used in the debugging of iOS applications). The point is, there are a multitude of ways developers try to thwart our efforts as pen testers. That discussion, however, is beyond the scope of this post. You are encouraged to check out the resources included in the references section. Of the resources listed, The Mobile Application Hackers Handbook does a great job covering the topic.

Simple PoC
We begin with bypassing routines that check for known file paths. This approach will lay the foundation for bypassing the other checks later on. To demonstrate this, I wrote a very simple PoC that checks for the existence of some these files. In the event one is found, the program prints out a message stating the device is jailbroken. In a real world scenario, the application may perform a number of actions that include, but are not limited to, preventing you from accessing the application entirely or restricting access to parts of the application.
Figure 1: Jailbreak detection PoC
 
If you have a jailbroken device and would like to test this for yourself, you can use clang – the Clang C, C++, and Objective-C compiler to compile it from your Mac OS host. Refer to the man page for details on the following command.
clang -framework Foundation -arch armv7 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk/ jailbreak.c -o jailbreak -miphoneos-version-min=5.0
Once compiled, simply copy the binary to your jailbroken device and execute it from the command line. On a side note, Objective-C is a strict superset of C, and in most instances you will see jailbreak detections implemented in C/C++. A sample run of the program reveals that the device is jailbroken:
Figure 2: PoC execution showing device is jailbroken
 
One of the first steps during an assessment is static analysis on the binary. Let’s begin by viewing the symbols with the following command nm jailbreak

Figure 3: Static analysis – extracting symbol information
 
Luckily for us, symbols have not been stripped, and based on the above, the _isJailBrokenmethod looks like the function responsible for determining the state of the device.
Figure 4: Examining the binary in IDA
 
The isJailBrokenmethod is called at 0000BE22, after which the value in R0 is compared to 0. Recall from earlier that the return value from a function call is stored in the R0 register. Let’s confirm this in gdb. We will set a break point at 0000BE28the BEQ (branch if eq) instruction and examine the contents of the R0 register.

Figure 5: Examining the contents of the R0 register

As expected the value at R0 is 1, and the program takes the branch that prints the message “Device is JAILBROKEN”. Our goal then is to take the other branch. Let’s examine the isJailBroken function.

Figure 6: isJailBroken function analysis

At 0000BEA0, the stat function is called, and at 0000BEA8, R0 is compared to 0. If the value is not zero, meaning the path hasn’t been found, the program processes the next file path in the jbFiles[] array shown in the PoC earlier on. However, if the path was found, we see R0 is set to 1 before the program returns and eventually exits.

Figure 7: Determining where R0 register is set

This above snippet corresponds to the following section in our PoC:

Figure 8: R0 gets set to 1 if artifact found
 
So if we update this, and instead of moving 1 in R0 we move a 0, we should be able to bypass the jailbreak detection check and thus get of jail. Let’s make this modification and run our binary again.
Figure 9: Updating R0 register to 0
 
Linking this to our PoC, it is the equivalent of doing:
Figure 10: Effect of setting R0 to 0
 
In other words, the isJailBroken function will always return 0. Let’s set another breakpoint after the comparison like we did before and examine the value in R0. If we are right, then according to the following snippet, we should branch to loc_BE3C and defeat the check.
Figure 11: PoC snippet
 
As expected the value is now 0, and when we continue program execution we get our desired result.

Figure 12: Bypassing the detection
 
But what if the binary has been stripped?
Earlier we said that we were lucky because the binary was not stripped, so we had the symbol information. Suppose however, that the developer decided to make our job a bit more difficult by stripping the binary (in our case we used strip <binaryname>). In this case, our approach would be a bit different. Let’s first look at the stripped binary using the nm tool:
Figure 13: Stripped binary
 
And then with gdb on the jailbroken mobile device:
Figure 14: Examining the stripped binary in gdb
 
It should be immediately clear that we now have a lot less information to work with. In the case of gdb, we now see “No symbol table is loaded”. Where has our isJailBrokensymbol gone? Let’s push ahead with our analysis by running strings on the binary.
Figure 15: Extracting strings from the binary
 
Ok, so we seem to be getting closer as we can see some familiar messages. Let’s head back to IDA once again:
Figure 16: Disassembled stripped binary
 
This certainly looks different from what we saw when the symbols were included. Nonetheless, let’s find the references to the strings we saw earlier. You can use the strings view in IDA and then use Ctrl+X to find all references to where they are used.
Figure 17: Locating references to the status message
 
Navigating to the highlighted location, we again see the familiar CMP R0, #0:
Figure 18: Locating CMP R0, #0
 
And if we go to the highlighted sub_BE54, we end up in our isJailBroken function. From that point on, it’s a repeat of what we already discussed.
Ok, but the functions are now inline
Another practice that is often recommended is to inline your functions. This causes the compiler to embed the full body of the function, as opposed to making a function call. With this in mind, our modified isJailBroken function declaration now looks like this:
Figure 19: Declaring functions inline
 
Before we continue, let’s remind ourselves of what the disassembled binary looked like prior to this change:

Figure 20: Binary before inline function
 
Now, let’s examine the modified binary:
Figure 21: Modified binary with function now inline
The _isJailBrokenmethod has now been inlined, and we no longer see the call(bl) instruction at 0000BE22 as before. Note that the original function body is still stored in the binary:
Figure 22: Function body still stored despite being inline
 
To prevent this, some very astute developers will go a step further and make the function static thereby removing the function body. The new function declaration will now be:
Figure 23: Static inline function
 
Again let’s look at this in IDA.
Figure 24: Disassembled inline binary
 
Instead of R0 being set from a function call as we saw previously, it is set from a value read from the stack using the LDRcommand at 0000BE9C. On closer examination we see the R0 register being set at 0000BE8Aand 0000BE98 and then stored on the stack:
Figure 25: Disassembled inline binary
At this point it’s the same process as before, we just need to move a 0 into R0at location 0000BE8A. And the rest is history.
Let’s block debugging then
We hinted at this earlier, when we said that the ptrace() system call is used when debugging an application. Let’s examine one implementation often used by developers:
Figure 26: ptrace function declaration
 
Figure 27: ptrace implementation
 
See the references section for additional details and source of the above code snippet. If we run our modified binary on the device and try to debug it as we have been doing with gdb, we are presented with the following:
Figure 28: Unable to use gdb
We were stopped in our tracks. Also, keep in mind that the function was inlined and the binary stripped of symbols. Examining it in IDA reveals the following:

Figure 29: Disassembled binary with call to ptrace_ptr
Pay special attention to the highlighted area. Recall from earlier, we said function arguments are in registers R0-R3. The ptrace_ptr call takes four arguments the first being PT_DENY_ATTACH with a value of 31. The /usr/include/sys/ptrace.h header file reveals the list of possible values:
Figure 30: Snippet ptrace documentation
 
So what happens if we pass a value that is outside of the expected values? The parameter is set at 0000BDF2 and later passed as the parameter to ptrace_ptrat 0000BDFC. We see a value of 1F, which translates, to 31 in decimal. Lets update this to 0x7F.
Figure 31: Updating PT_DENY_ATTACH to random value
 
We copy the modified binary back to our device and have our bypass.
Figure 32: Bypassing PT_DENY_ATTACH
 
Another oft recommended technique for determining if a debugger is attached is the use of the sysctl()function. Now it doesn’t explicitly prevent a debugger from being attached, but it does return enough information for you to determine whether you are debugging the application. The code is normally a variation of the following:
Figure 33: Using sysctl()
When we run this from gdb, we get:
Figure 34: Output from running with sysctl()
Let’s pop this in IDA. Again the binary has been stripped and the checkDebugger function inlined.
Figure 35: Call to sysctl()
At 0000BE36we see the sysctl() function call and at 0000BE3A we see the comparison of register R0 to -1. If the call was not successful, then at 0000BE40 the program copies 1 to R0 before returning. That logic corresponds to:
Figure 36: Code snippet showing call to sysctl()
The fun begins when sysctl() was successful. We see the following snippet:
Figure 37: A look at the ternary operator
This corresponds to the following code snippet:
Figure 38: Ternary operator in our source code
When the application is being debugged/traced, the kernel sets the P_TRACED flag for the process where P_TRACED is defined in /usr/include/sys/proc.h as:
Figure 39: P_TRACED definition in /usr/include/sys/proc.h
 
So at 0000BE4Awe see the bitwise AND against this value. In effect, the loc_BE46 block corresponds to the above ternary operator in the return statement. What we want then is for this call to return 0.
If we change the instruction at 0000BE46 to a MOVS R0, 0 instead:
Figure 40: Patching the binary
 
When we run the program again we get
Figure 41: Successful bypass
 
Now, you may be asking, how did we know to update that specific instruction? Well, as we said, the loc_BE46 block corresponds to the use of the ternary operator in our code. Now don’t allow the compiler’s representation of the operator to confuse you. The ternary operator says if the process is being traced return 1 otherwise return 0. At 0000BE46 R0 is set to 1, and R0is also set at 0000BE5C.[EW1] However, in the latter case, the register is set in a conditional block. That block gets hit when the check returns 0. In other words, the process is not being traced. Let’s look at this in gdb. We will set a breakpoint at 0000BE5E, the point at which R0gets stored on the stack at [sp,#0x20].
Figure 42: Inspecting the R0 register
As you can see, R0has a value of 1, and this was set at 0000BE46 as discussed earlier. This value is then written to the stack and later accessed at 0000BE60 to determine if the process is being traced. We see the comparison against 0 at 0000BE62, and if it’s true, we take the path that shows we bypassed the debug check.
Figure 43: Reversing the binary
So, if we set a breakpoint at 0000BE60 and look what value was read from the stack, we see the following:
Figure 44: Examining the value in R0 that will be checked to determine if process is being debugged
This value(0x00000001) is the 1 that was copied to R0 earlier on. Hence, updating this to 0 helps achieve our goal.
Bringing down the curtains
Before we go, let’s revisit our very first example:
Figure 45: Revisiting first example
Recall we modified the isJailBroken function by setting register R0 to 0. However, there is a much simpler way to achieve our objective, and some of you would have already picked it up. The instruction at 0000BE28 is BEQ (branch if eq), so all we really need to do is change this to an unconditional jump to loc_BE3C. After the modification we end up with:
Figure 46: Updated conditional jump to unconditional jump
And we are done, however, we had to take the long scenic route first.
 
Conclusion
As we demonstrated, each time the developer added a new measure, we were able to bypass it. This however does not mean that the measures were completely ineffective. It just means that developers should implement these and other measures to guard against this type of activity. There is no silver bullet.
From a pen tester’s stand point, it comes down to time and effort. No matter how complex the function, at some point it has to return a value, and it’s a matter of finding that value and changing it to suit our needs.
Detecting jailbreaks will continue to be an interesting topic. Remember, however, that an application running at a lower privilege can be tampered with by one that is at a higher privilege. A jailbroken device can run code in kernel-mode and can therefore supply false information to the application about the state of the device.
Happy hacking.
 
References:
  1. http://www.amazon.com/The-Mobile-Application-Hackers-Handbook/dp/1118958500
  2. http://www.amazon.com/Practical-Reverse-Engineering-Reversing-Obfuscation/dp/1118787315
  3. http://www.amazon.com/Hacking-Securing-iOS-Applications-Hijacking/dp/1449318746
  4. https://www.owasp.org/index.php/IOS_Application_Security_Testing_Cheat_Sheet
  5. https://www.theiphonewiki.com/wiki/Bugging_Debuggers
  6. http://www.opensource.apple.com/source/xnu/xnu-792.13.8/bsd/sys/ptrace.h