Month: March 2015

Running Invisible in the Background in iOS 8

Since iOS 8’s release, a number of security improvements have been made since publishing my findings last July. Many services that posed a threat to user privacy have been since closed off, and are only open in beta versions of iOS. One small point I made in the paper was the threat that invisible software poses on the operating system:

“Malicious software does not require a device be jail- broken in order to run. … With the simple addition of an SBAppTags property to an application’s Info.plist (a required file containing descriptive tags iden- tifying properties of the application), a developer can build an application to be hidden from the user’s GUI (SpringBoard). This can be done to a non-jailbroken device if the attacker has purchased a valid signing certificate from Apple. While advanced tools, such as Xcode, can detect the presence of such software, the application is invisible to the end-user’s GUI, as well as in iTunes. In addition to this, the capability exists of running an application in the background by masquerading as a VoIP client (How to maintain VOIP socket connection in background) or audio player (such as Pandora) by add- ing a specific UIBackgroundModes tag to the same property list file. These two features combined make for the perfect skeleton for virtually undetectable spyware that runs in the background.”

As of iOS 8, Apple has closed off the SBAppTags feature set so that applications cannot use that to hide applications, however it looks like there are still some ways to manipulate the operating system into hiding applications on the device. I have contacted Apple with the specific technical details and they have assured me that the problem has been fixed in iOS 8.3. As for now, however, it looks like iOS 8.2 and lower are still vulnerable to this attack. The attack allows for software to be loaded onto a non-jailbroken device (which typically requires a valid pairing, or physical possession of the device) that runs in the background and invisibly to the SpringBoard user interface.

The presence of a vulnerability such as this should heighten user awareness that invisible software may still be installed on a non-jailbroken device, and would be capable of gathering information that could be used to track the user over a period of time. If you suspect that malware may be running on your device, you can view software running invisibly with a copy of Xcode. Unlike the iPhone’s UI and iTunes, invisible software that is installed on the device will show up under Xcode’s device organizer.

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Testing for the Strawhorse Backdoor in Xcode

In the previous blog post, I highlighted the latest Snowden documents, which reveal a CIA project out of Sandia National Laboratories to author a malicious version of Xcode. This Xcode malware targeted App Store developers by installing a backdoor on their computers to steal their private codesign keys.

Screen Shot 2015-03-10 at 2.09.50 PM

So how do you test for a backdoor you’ve never seen before? By verifying that the security mechanisms it disables are working correctly. Based on the document, the malware apparently infects Apple’s securityd daemon to prevent it from warning the user prior to exporting developer keys:

“… which rewrites securityd so that no prompt appears when exporting a developer’s private key”

A good litmus test to see if securityd has been compromised in this way is to attempt to export your own developer keys and see if you are prompted for permission.

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The Implications of CIA’s Jamboree

Early this morning, The Intercept posted several documents pertaining to CIA’s research into compromising iOS devices (along with other things) through Sandia National Laboratories, a major research and development contractor to the government. The documents outlined a number of project talks taking place at a closed government conference referred to as the Jamboree in 2012. The projects listed in the documents included the following pieces.


Rocoto, a chip-like implant that would likely be soldered to the 30-pin connector on the main board, and act like a flasher box that performs the task of jailbreaking a device using existing public techniques. Once jailbroken, a chip like Rocoto could easily install and execute code on the device for persistent monitoring or other forms of surveilance. Upon firmware restore, a chip like Rocoto could simply re-jailbreak the device. Such an implant could have likely worked persistently on older devices (like the 3G mentioned), however the wording of the document (“we will discuss efforts”) suggests the implant was not complete at the time of the talk. This may, however, have later been adopted into the DROPOUTJEEP implant, which was portrayed as an operational product in the NSA’s catalog published several months ago. The DROPOUTJEEP project, however, claimed to be software-based, where Rocoto seems to have involved a physical chip implant.


Strawhorse, a malicious implementation of Xcode, where App Store developers (likely not suspected of any crimes) would be targeted, and their dev machines backdoored to give CIA injection capabilities into compiled applications. The malicious Xcode variant was capable of stealing the developer’s private codesign keys, which would be smuggled out with compiled binaries. It would also disable securityd so that it would not warn the developer that this was happening. The stolen keys could later be used to inject and sign payloads into the developer’s own products without their permission or knowledge, which could then be widely disseminated through the App Store channels. This could include trojans or watermarks, as the document suggests. With the developer keys extracted, binary modifications could also be made at a later time, if such an injection framework existed.

In spite of what The Intercept wrote, there is no evidence that Strawhorse was slated for use en masse, or that it even reached an operational phase.

NOTE: At the time these documents were reportedly created, a vast majority of App Store developers were American citizens. Based on the wording of the document, this was still in the middle stages of development, and an injection mechanism (the complicated part) does not appear to have been developed yet, as there was no mention of it.

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