Terminals used in other countries, especially in Europe, use a different communications protocol called OPI (Open Payment Initiative) that is similar to ZVT, but lacks the remote management functionality that attackers can abuse.
However, some terminal manufacturers added proprietary extensions to OPI to implement that functionality, because they like the comfort of remote management, Nohl said. "At least we've seen this in a few cases. We can't guarantee that it's widespread, but every implementation of OPI that we've looked at had extensions that brought back remote manageability, and like in ZVT, it wasn't secure."
With magnetic stripe data and associated PIN numbers attackers can clone payment cards and perform fraud, even in countries where chip-protected (EMV) cards are widely deployed.
EMV-capable terminals still support magstripe-based transactions for cards that don't have a chip, and verifying whether the card has a chip or not is usually done by checking a specific bit stored on the magnetic stripe. So an attacker can simply change that bit on his cloned card, Nohl said.
Another attack that the SRLabs team found possible through ZVT is to force a terminal to associate with a different merchant account, like one controlled by a hacker, and which would receive all the money from transactions performed through that terminal.
This can be done by a man-in-the-middle attack through a password-protected command that instructs the terminal to change its ID to one that the payment processor associates with a different merchant. The password is the same for all terminals tied to a specific processor, the SRLabs researchers found.
When the terminal ID changes, the processor will send a new configuration back to the terminal including the new merchant's transaction limits and banner -- the merchant identifying information that appears on the printed receipts. The attacker can actually intercept this information and change it so that receipts retain the old merchant's banner, while the money is funneled to the different account controlled by the attacker.
A third attack is possible through the Poseidon protocol that's also widely used in Germany and in some other countries like France, Luxembourg and Iceland. This protocol is used by terminals to communicate with the backend servers of payment processors and is a variation of an international standard called ISO 8583.
Payment terminals require a secret key to authenticate with payment processors over the Poseidon protocol. However, like with ZVT, payment terminal manufacturers implemented the same authentication key across all of their terminals, SRLabs found.
This error can be abused to steal money from merchant accounts. While most transactions add money to such accounts in exchange for goods or services, there are a few that can cost merchants money, for example transaction refunds or top-up vouchers like those used to recharge prepaid SIM cards.
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