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Bypassing Passcodes in iOS

Last week, a story was going around explaining how to brute-force an iOS password. Basically, the trick was to plug the phone into an external keyboard and trying every PIN at once:

We reported Friday on Hickey’s findings, which claimed to be able to send all combinations of a user’s possible passcode in one go, by enumerating each code from 0000 to 9999, and concatenating the results in one string with no spaces. He explained that because this doesn’t give the software any breaks, the keyboard input routine takes priority over the device’s data-erasing feature.

I didn’t write about it, because it seemed too good to be true. A few days later, Apple pushed back on the findings — and it seems that it doesn’t work.

This isn’t to say that no one can break into an iPhone. We know that companies like Cellebrite and Grayshift are renting/selling iPhone unlock tools to law enforcement — which means governments and criminals can do the same thing — and that Apple is releasing a new feature called “restricted mode” that may make those hacks obsolete.

Grayshift is claiming that its technology will still work.

Former Apple security engineer Braden Thomas, who now works for a company called Grayshift, warned customers who had bought his GrayKey iPhone unlocking tool that iOS 11.3 would make it a bit harder for cops to get evidence and data out of seized iPhones. A change in the beta didn’t break GrayKey, but would require cops to use GrayKey on phones within a week of them being last unlocked.

“Starting with iOS 11.3, iOS saves the last time a device has been unlocked (either with biometrics or passcode) or was connected to an accessory or computer. If a full seven days (168 hours) elapse [sic] since the last time iOS saved one of these events, the Lightning port is entirely disabled,” Thomas wrote in a blog post published in a customer-only portal, which Motherboard obtained. “You cannot use it to sync or to connect to accessories. It is basically just a charging port at this point. This is termed USB Restricted Mode and it affects all devices that support iOS 11.3.”

Whether that’s real or marketing, we don’t know.

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Perverse Vulnerability from Interaction between 2-Factor Authentication and iOS AutoFill

Apple is rolling out an iOS security usability feature called Security code AutoFill. The basic idea is that the OS scans incoming SMS messages for security codes and suggests them in AutoFill, so that people can use them without having to memorize or type them.

Sounds like a really good idea, but Andreas Gutmann points out an application where this could become a vulnerability: when authenticating transactions:

Transaction authentication, as opposed to user authentication, is used to attest the correctness of the intention of an action rather than just the identity of a user. It is most widely known from online banking, where it is an essential tool to defend against sophisticated attacks. For example, an adversary can try to trick a victim into transferring money to a different account than the one intended. To achieve this the adversary might use social engineering techniques such as phishing and vishing and/or tools such as Man-in-the-Browser malware.

Transaction authentication is used to defend against these adversaries. Different methods exist but in the one of relevance here — which is among the most common methods currently used — the bank will summarise the salient information of any transaction request, augment this summary with a TAN tailored to that information, and send this data to the registered phone number via SMS. The user, or bank customer in this case, should verify the summary and, if this summary matches with his or her intentions, copy the TAN from the SMS message into the webpage.

This new iOS feature creates problems for the use of SMS in transaction authentication. Applied to 2FA, the user would no longer need to open and read the SMS from which the code has already been conveniently extracted and presented. Unless this feature can reliably distinguish between OTPs in 2FA and TANs in transaction authentication, we can expect that users will also have their TANs extracted and presented without context of the salient information, e.g. amount and destination of the transaction. Yet, precisely the verification of this salient information is essential for security. Examples of where this scenario could apply include a Man-in-the-Middle attack on the user accessing online banking from their mobile browser, or where a malicious website or app on the user’s phone accesses the bank’s legitimate online banking service.

This is an interesting interaction between two security systems. Security code AutoFill eliminates the need for the user to view the SMS or memorize the one-time code. Transaction authentication assumes the user read and approved the additional information in the SMS message before using the one-time code.

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New iPhone OS May Include Device-Unlocking Security

iOS 12, the next release of Apple’s iPhone operating system, may include features to prevent someone from unlocking your phone without your permission:

The feature essentially forces users to unlock the iPhone with the passcode when connecting it to a USB accessory everytime the phone has not been unlocked for one hour. That includes the iPhone unlocking devices that companies such as Cellebrite or GrayShift make, which police departments all over the world use to hack into seized iPhones.

“That pretty much kills [GrayShift’s product] GrayKey and Cellebrite,” Ryan Duff, a security researcher who has studied iPhone and is Director of Cyber Solutions at Point3 Security, told Motherboard in an online chat. “If it actually does what it says and doesn’t let ANY type of data connection happen until it’s unlocked, then yes. You can’t exploit the device if you can’t communicate with it.”

This is part of a bunch of security enhancements in iOS 12:

Other enhancements include tools for generating strong passwords, storing them in the iCloud keychain, and automatically entering them into Safari and iOS apps across all of a user’s devices. Previously, standalone apps such as 1Password have done much the same thing. Now, Apple is integrating the functions directly into macOS and iOS. Apple also debuted new programming interfaces that allow users to more easily access passwords stored in third-party password managers directly from the QuickType bar. The company also announced a new feature that will flag reused passwords, an interface that autofills one-time passwords provided by authentication apps, and a mechanism for sharing passwords among nearby iOS devices, Macs, and Apple TVs.

A separate privacy enhancement is designed to prevent websites from tracking people when using Safari. It’s specifically designed to prevent share buttons and comment code on webpages from tracking people’s movements across the Web without permission or from collecting a device’s unique settings such as fonts, in an attempt to fingerprint the device.

The last additions of note are new permission dialogues macOS Mojave will display before allowing apps to access a user’s camera or microphone. The permissions are designed to thwart malicious software that surreptitiously turns on these devices in an attempt to spy on users. The new protections will largely mimic those previously available only through standalone apps such as one called Oversight, developed by security researcher Patrick Wardle. Apple said similar dialog permissions will protect the file system, mail database, message history, and backups.

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Impersonating iOS Password Prompts

This is an interesting security vulnerability: because it is so easy to impersonate iOS password prompts, a malicious app can steal your password just by asking.

Why does this work?

iOS asks the user for their iTunes password for many reasons, the most common ones are recently installed iOS operating system updates, or iOS apps that are stuck during installation.

As a result, users are trained to just enter their Apple ID password whenever iOS prompts you to do so. However, those popups are not only shown on the lock screen, and the home screen, but also inside random apps, e.g. when they want to access iCloud, GameCenter or In-App-Purchases.

This could easily be abused by any app, just by showing an UIAlertController, that looks exactly like the system dialog.

Even users who know a lot about technology have a hard time detecting that those alerts are phishing attacks.

The essay proposes some solutions, but I’m not sure they’ll work. We’re all trained to trust our computers and the applications running on them.

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Another iPhone Change to Frustrate the Police

I recently wrote about the new ability to disable the Touch ID login on iPhones. This is important because of a weirdness in current US law that protects people’s passcodes from forced disclosure in ways it does not protect actions: being forced to place a thumb on a fingerprint reader.

There’s another, more significant, change: iOS now requires a passcode before the phone will establish trust with another device.

In the current system, when you connect your phone to a computer, you’re prompted with the question “Trust this computer?” and you can click yes or no. Now you have to enter in your passcode again. That means if the police have an unlocked phone, they can scroll through the phone looking for things but they can’t download all of the contents onto a another computer without also knowing the passcode.

More details:

This might be particularly consequential during border searches. The “border search” exception, which allows Customs and Border Protection to search anything going into the country, is a contentious issue when applied electronics. It is somewhat (but not completely) settled law, but that the U.S. government can, without any cause at all (not even “reasonable articulable suspicion”, let alone “probable cause”), copy all the contents of my devices when I reenter the country sows deep discomfort in myself and many others. The only legal limitation appears to be a promise not to use this information to connect to remote services. The new iOS feature means that a Customs office can browse through a device — a time limited exercise — but not download the full contents.

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iOS 11 Allows Users to Disable Touch ID

A new feature in Apple’s new iPhone operating system — iOS 11 — will allow users to quickly disable Touch ID.

A new setting, designed to automate emergency services calls, lets iPhone users tap the power button quickly five times to call 911. This doesn’t automatically dial the emergency services by default, but it brings up the option to and also temporarily disables Touch ID until you enter a passcode.

This is useful in situations where the police cannot compel you to divulge your password, but can compel you to press your finger on the reader.

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Security Vulnerabilities in Mobile MAC Randomization

Interesting research: “A Study of MAC Address Randomization in Mobile Devices When it Fails“:

Abstract: Media Access Control (MAC) address randomization is a privacy technique whereby mobile devices rotate through random hardware addresses in order to prevent observers from singling out their traffic or physical location from other nearby devices. Adoption of this technology, however, has been sporadic and varied across device manufacturers. In this paper, we present the first wide-scale study of MAC address randomization in the wild, including a detailed breakdown of different randomization techniques by operating system, manufacturer, and model of device. We then identify multiple flaws in these implementations which can be exploited to defeat randomization as performed by existing devices. First, we show that devices commonly make improper use of randomization by sending wireless frames with the true, global address when they should be using a randomized address. We move on to extend the passive identification techniques of Vanhoef et al. to effectively defeat randomization in 96% of Android phones. Finally, we show a method that can be used to track 100% of devices using randomization, regardless of manufacturer, by exploiting a previously unknown flaw in the way existing wireless chipsets handle low-level control frames.

Basically, iOS and Android phones are not very good at randomizing their MAC addresses. And tricks with level-2 control frames can exploit weaknesses in their chipsets.

Slashdot post.

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