Today we will take a first look at malware-based attacks on ATMs in general, while future articles will go into more detail on the individual subtopics.
ATMs have been robbed by criminal gangs around the world for decades. A successful approach since ~ 20 years is the use of highly flammable gas, which is fed into the ATM safe and ignited during a robbery. For an attacker, this is an inexpensive way to get the cash, but it also leads to great publicity and thus risk of being caught by security authorities. In addition, more and more vending machines are being equipped with systems that ink the money as soon as the machine is physically breached.
Since the beginning of the 2010s, there has been a trend for more and more criminal gangs to switch to non-violent methods without explosives. We are talking about so-called physical malware attacks. Here, malicious software is brought onto the PC inside the ATM, for example, via a USB stick. This malware-based attack usually results in all cash inside the safe being ejected via the regular dispensing mechanism (cash-out attack). A successful attack would effectively put the malware in full command over the ATM thereby rendering it almost impossible to stop them.
Another aspect that cannot be ignored is that an infected ATM often enables attacks on other devices or services within the network. For example, for research and testing purposes, we were able to develop a malware that attacked all ATMs within the network from an infected device (initial ATM). The result was simultaneous cash withdrawal from all ATMs within the shared network. It was also interesting here that other devices such as a Raspberry Pi connected to the same network could achieve the same results as well.
Even though during the Covid pandemic in 2020 such malware-based attacks on ATMs decreased, a clear increase has been visible since the beginning of 2022. Malware to attack specific types of devices can be purchased today for about 1000USD within the darknet.
To protect against such attacks, it is necessary to prevent malware from being installed and executed. Through years of research and experience in real projects, we have been able to help ATM manufacturers and banks protect their devices from such attacks.
Generally, an ATM consists of two components:
Safe
Cabinet
The computer inside the cabinet usually runs on the Windows operating system, which in turn runs the application for legitimate use of the ATM. A user / bank customer should not be able to break out of this application (e.g. via the touchscreen) to access the underlying system. For this purpose, Windows generally runs in the so-called Kiosk mode, which limits the input options only to the necessary user functions within the application.
Input values within the user application via the touchscreen or pin pad, for example, are in turn processed by the software and then transmitted to other devices such as the cash dispenser via corresponding commands. This communication between the user application and internal devices takes place via the XFS standard (Extensions for Financial Services). This standard provides an interface (API) for the Windows Hardware Manager via which all applications can access it.
When the user initiates a transaction such as a cash withdrawal, the bank’s processing center is also contacted, which validates the transaction and ultimately transmits the confirmation for withdrawal. The connection between the ATM and the processing center is generally made via a cable, but occasionally also wirelessly (WiFi or GSM).
Overview ATM
In general, we classify ATM vulnerabilities regarding malware attacks into three categories. The combination of vulnerabilities from these categories allows an attacker to dispense all cash or attack other systems on the same network in many cases.
Insufficient physical security
The first step for malware-based attacks is usually to open the cabinet in order to interact with the integrated computer via a plugged-in keyboard or special USB stick. Here, we came into contact with recurring security vulnerabilities in various assessments:
Computer inside the cabinet with open USB ports
Insufficient configuration of the system and peripheral devices
It is often the case that the XFS standard for communication between OS and peripherals is configured very insecurely. There is often no authentication at all between the peripherals and the OS. An attacker with access to the computer could execute malware to communicate with the cash dispenser, and thus cash-out all available money. In summary, we found the following recurring security flaws in the system and device configurations:
ATM allows breaking out of the banking application using a connected keyboard, exposing that the current user has full administrative access.
Insufficient network security
An attacker with access to the ATM’s network interface (e.g. Ethernet) can attack other systems or services within the network. In one of our scenarios, it was even possible to dispense cash from all ATMs within the network. In general, such scenarios are based on the following vulnerabilities:
Example – Bypassing outdated NAC (Network Access Control) with public tools
Due to the large number of possible vulnerabilities, individual malware-based attack scenarios often arise. The following figure shows general attack scenarios, which are also performed in our assessments.
In general, it is difficult to make all-encompassing recommendations for securing ATMs. Even in our current assessments, we are increasingly confronted with new and very individual security vulnerabilities. However, we can make general recommendations for securing ATMs against malware attacks, as some vulnerabilities are present on a regular basis:
Malware-based attacks that rely on physical access are becoming increasingly popular. Today, however, we can already see some security improvements in current assessments. However, our experience shows that the improvement within the last years is still insufficient. Many protections could still be circumvented to exploit initial vulnerabilities. This is usually not because manufacturers and banks deliberately avoid security precautions, but because the whole environment and its processes often do not allow simple security upgrades. Some examples are that to ensure proper network access control (NAC), all switches within all branches would have to be replaced, technical staff still needs an interface (e.g. USB) to perform administrative tasks on the ATM, etc.
In general, it turns out that criminal hacker gangs are always one step ahead and find ways to bypass current security measurements.
Alexander Poth
Alexander is a senior security consultant at NVISO. He regularly performs a variety of assessments, including IoT and embedded devices, Web and Mobile applications.