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iOS and Android juice jacking defenses have been trivial to bypass for years

SON OF JUICE JACKING ARISES

New ChoiceJacking attack allows malicious chargers to steal data from phones.

Dan Goodin
–

Apr 28, 2025 7:00 am

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Credit:

Aurich Lawson | Getty Images

Credit:

Aurich Lawson | Getty Images

About a decade ago, Apple and Google started updating iOS and Android, respectively, to make them less susceptible to “juice jacking,” a form of attack that could surreptitiously steal data or execute malicious code when users plug their phones into special-purpose charging hardware. Now, researchers are revealing that, for years, the mitigations have suffered from a fundamental defect that has made them trivial to bypass.

“Juice jacking” was coined in a 2011 article on KrebsOnSecurity detailing an attack demonstrated at a Defcon security conference at the time. Juice jacking works by equipping a charger with hidden hardware that can access files and other internal resources of phones, in much the same way that a computer can when a user connects it to the phone.

An attacker would then make the chargers available in airports, shopping malls, or other public venues for use by people looking to recharge depleted batteries. While the charger was ostensibly only providing electricity to the phone, it was also secretly downloading files or running malicious code on the device behind the scenes. Starting in 2012, both Apple and Google tried to mitigate the threat by requiring users to click a confirmation button on their phones before a computer—or a computer masquerading as a charger—could access files or execute code on the phone.

The logic behind the mitigation was rooted in a key portion of the USB protocol that, in the parlance of the specification, dictates that a USB port can facilitate a “host” device or a “peripheral” device at any given time, but not both. In the context of phones, this meant they could either:

Host the device on the other end of the USB cord—for instance, if a user connects a thumb drive or keyboard. In this scenario, the phone is the host that has access to the internals of the drive, keyboard or other peripheral device.

Act as a peripheral device that’s hosted by a computer or malicious charger, which under the USB paradigm is a host that has system access to the phone.

An alarming state of USB security

Researchers at the Graz University of Technology in Austria recently made a discovery that completely undermines the premise behind the countermeasure: They’re rooted under the assumption that USB hosts can’t inject input that autonomously approves the confirmation prompt. Given the restriction against a USB device simultaneously acting as a host and peripheral, the premise seemed sound. The trust models built into both iOS and Android, however, present loopholes that can be exploited to defeat the protections. The researchers went on to devise ChoiceJacking, the first known attack to defeat juice-jacking mitigations.

“We observe that these mitigations assume that an attacker cannot inject input events while establishing a data connection,” the researchers wrote in a paper scheduled to be presented in August at the Usenix Security Symposium in Seattle. “However, we show that this assumption does not hold in practice.”

The researchers continued:

We present a platform-agnostic attack principle and three concrete attack techniques for Android and iOS that allow a malicious charger to autonomously spoof user input to enable its own data connection. Our evaluation using a custom cheap malicious charger design reveals an alarming state of USB security on mobile platforms. Despite vendor customizations in USB stacks, ChoiceJacking attacks gain access to sensitive user files (pictures, documents, app data) on all tested devices from 8 vendors including the top 6 by market share.

In response to the findings, Apple updated the confirmation dialogs in last month’s release of iOS/iPadOS 18.4 to require a user authentication in the form of a PIN or password. While the researchers were investigating their ChoiceJacking attacks last year, Google independently updated its confirmation with the release of version 15 in November. The researchers say the new mitigation works as expected on fully updated Apple and Android devices. Given the fragmentation of the Android ecosystem, however, many Android devices remain vulnerable.

All three of the ChoiceJacking techniques defeat the original Android juice-jacking mitigations. One of them also works against those defenses in Apple devices. In all three, the charger acts as a USB host to trigger the confirmation prompt on the targeted phone.

The attacks then exploit various weaknesses in the OS that allow the charger to autonomously inject “input events” that can enter text or click buttons presented in screen prompts as if the user had done so directly into the phone. In all three, the charger eventually gains two conceptual channels to the phone: (1) an input one allowing it to spoof user consent and (2) a file access connection that can steal files.

An illustration of ChoiceJacking attacks. (1) The victim device is attached to the malicious charger. (2) The charger establishes an extra input channel. (3) The charger initiates a data connection. User consent is needed to confirm it. (4) The charger uses the input channel to spoof user consent.

Credit:
Draschbacher et al.

Credit:

Draschbacher et al.

It’s a keyboard, it’s a host, it’s both

In the ChoiceJacking variant that defeats both Apple- and Google-devised juice-jacking mitigations, the charger starts as a USB keyboard or a similar peripheral device. It sends keyboard input over USB that invokes simple key presses, such as arrow up or down, but also more complex key combinations that trigger settings or open a status bar.

The input establishes a Bluetooth connection to a second miniaturized keyboard hidden inside the malicious charger. The charger then uses the USB Power Delivery, a standard available in USB-C connectors that allows devices to either provide or receive power to or from the other device, depending on messages they exchange, a process known as the USB PD Data Role Swap.

A simulated ChoiceJacking charger. Bidirectional USB lines allow for data role swaps.

Credit:
Draschbacher et al.

A simulated ChoiceJacking charger. Bidirectional USB lines allow for data role swaps.

Credit:

Draschbacher et al.

With the charger now acting as a host, it triggers the file access consent dialog. At the same time, the charger still maintains its role as a peripheral device that acts as a Bluetooth keyboard that approves the file access consent dialog.

The full steps for the attack, provided in the Usenix paper, are:

1. The victim device is connected to the malicious charger. The device has its screen unlocked.

2. At a suitable moment, the charger performs a USB PD Data Role (DR) Swap. The mobile device now acts as a USB host, the charger acts as a USB input device.

3. The charger generates input to ensure that BT is enabled.

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