Boffins from the University of Birmingham and the University of Surrey exploited a series of vulnerabilities in an attack against iPhone owners using Apple Pay and Visa payment cards.
The researchers explained that the attack could allow an unauthenticated attacker to steal money from the targeted iPhone when it is configured to use Apple Pay and a Visa card in “transit mode.”
Experts pointed out that the attack also works against locked iPhones. Before going deep into the attack, let me introduce the “Express Transit” / “Express Travel” feature implemented in Apple Pay, which allows users to make a payment without having authorized the payment with Face ID or Touch ID.
This feature could be very useful while paying for public transportation.
The researchers attempted to simulate a similar scenario and emulated a ticket-barrier transaction by using a Proxmark device acting as a card reader communicating with the target iPhone and an Android phone with an NFC chip (acting as a card emulator) that communicated with a payment terminal.
In the attack scenario, hackers hold the reader emulator close to the targeted iPhone.
The attack devised by the researchers is an active man-in-the-middle replay and relay attack, the Proxmark replays the “magic bytes” to the iPhone to trick it into believing that it’s a ticket-gate transaction that doesn’t require any user action to authorize the payment.
In order to carry out the attack, the experts enabled offline data authentication for online transactions through specific settings, this step was necessary because some readers may have intermittent connectivity (e.g. transit system entries).
“The attack works by first replaying the Magic Bytes to the iPhone, such that it believes the transaction is happening with a transport EMV reader. Secondly, while relaying the EMV messages, the Terminal Transaction Qualifiers (TTQ), sent by the EMV terminal, need to be modified such that the bits (flags) for Offline Data Authentication (ODA) for Online Authorizations supported and EMV mode supported are set. Offline data authentication for online transactions is a feature used in special-purpose readers, such as transit system entry gates, where EMV readers may have intermittent connectivity and online processing of a transaction cannot always take place. These modifications are sufficient to allow relaying a transaction to a non-transport EMV reader, if the transaction is under the contactless limit.” the researchers explained. “In order to relay transactions over the contactless limit, the Card Transaction Qualifiers (CTQ), sent by the iPhone, need to be modified such that the bit (flag) for Consumer Device Cardholder Verification Method is set. This tricks the EMV reader into believing that on-device user authentication has been performed (e.g. by fingerprint). “
The researchers were also able to steal an amount of money over the limit of the contactless card transactions, they published a video PoC that demonstrates that was possible to steal steal £1,000 ($1,300) from a locked phone.
The the attack does not work if Apple Pay is used with Mastercard cards.
The experts shared their findings with both Visa and Apple and also provided recommendations on how to mitigate the attack. Both companies have yes to fix the vulnerabilities exploited by the experts because they believe that the attack method proposed by the researchers is impractical in the real world.
“While either Visa or Apple implement a fix for the problem, we recommend users to not use Visa as a transport card in Apple Pay. If your iPhone is lost or stolen, activate the Lost Mode on your iPhone, and call your bank to block your card.” conclude the experts.
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(SecurityAffairs – hacking, Apple Pay)