Embedded Linux Devices: Understanding the Threat Landscape

A look into the various types of attacks that embedded Linux systems are vulnerable to and know how to recognize and prevent them

Introduction

Like other types of Linux systems, Embedded Linux systems are vulnerable to a wide range of security threats. These systems are particularly susceptible to attack because they often have less powerful hardware and fewer resources than traditional Linux systems, making it harder to detect and defend against security threats. Additionally, specific classes of embedded systems are often deployed in remote and hard-to-reach locations, making it difficult to apply security updates and patches. Furthermore, many embedded systems have a long life cycle and may not be updated with the latest security patches and features, which makes them easy targets for attackers.

Some of the most common types of security threats that Embedded Linux systems face include the following:

Remote code execution (RCE)

This attack allows an attacker to execute arbitrary code on a remote system by exploiting vulnerabilities in the system's software or firmware. The attacker can use these vulnerabilities to gain unauthorized access to the system or perform other malicious actions. RCE vulnerabilities can be found in many different types of software, including the Linux kernel, libraries, and applications. Examples of known RCE vulnerabilities in Embedded Linux systems include:

1. Shellshock: This is a vulnerability in the Bash shell, a command-line interpreter commonly used in Linux and other Unix-like operating systems. The vulnerability allows an attacker to execute arbitrary code by injecting commands into the environment variables used by the Bash shell.
2. Ghost: This is a vulnerability in the GNU C library (Glibc), a widely-used library that provides essential system functions for Linux and other Unix-like operating systems. The vulnerability allows an attacker to execute arbitrary code by sending a specially-crafted request to a system that uses the vulnerable version of Glibc. This vulnerability was discovered in 2015 and affected many Embedded Linux systems.
3. Dirty Copy-On-Write: This vulnerability in the Linux kernel allows an attacker to gain write access to read-only memory mappings, which can be used to execute arbitrary code. This vulnerability affected all Linux-based systems,?including Android devices, that used older versions of the?Linux kernel?created before 2018.
4. Heartbleed: This vulnerability in the OpenSSL library is commonly used to provide secure communications for many different types of software. The vulnerability allows an attacker to access sensitive information, such as passwords and encryption keys, by sending a specially-crafted request to a system that uses the vulnerable version of OpenSSL. This vulnerability was discovered in 2014 and affected many Embedded Linux systems.

These are just a few examples of known RCE vulnerabilities that have previously affected Embedded Linux systems. Many other similar vulnerabilities have been discovered and continue to be found.

Man-in-the-Middle (MitM)

This attack occurs when an attacker intercepts and alters network traffic between two parties. This can be done by positioning themselves between the two parties by physically connecting to the network or exploiting vulnerabilities in the network infrastructure. On Linux systems, MitM attacks can occur in several ways. Some examples include:

1. ARP spoofing: This attack involves sending spoofed ARP (Address Resolution Protocol) messages on a local network to map the attacker's IP address to the target's MAC (Media Access Control) address. This allows the attacker to intercept and alter network traffic between the target and other devices on the network.
2. DNS spoofing: This attack involves intercepting and altering DNS (Domain Name System) requests and responses. This can redirect traffic to a malicious website, intercept sensitive information, or perform other malicious actions.
3. SSL/TLS spoofing: This attack involves intercepting and altering SSL/TLS (Secure Sockets Layer/Transport Layer Security) traffic. This can intercept sensitive information, such as login credentials and financial information, or perform other malicious actions.

A vulnerability in the Linux kernel allows an attacker to intercept and alter network traffic by exploiting a TCP/IP stack bug. This vulnerability was discovered in 2016 and affected many Embedded Linux systems.

Denial of service (DoS) attack?

An attack that aims to make a system or network resource unavailable to its intended users by overwhelming it with a large number of requests. This can be accomplished by using various techniques, such as flooding the system with many packets, exhausting system resources, or exploiting vulnerabilities in the system's software or firmware. On Linux systems, DoS attacks can occur in several ways. Examples include:

1. TCP/UDP flooding: This type of attack involves flooding the system with a large number of TCP or UDP packets. This can exhaust system resources, such as CPU and memory, and cause the system to crash or become unresponsive.
2. HTTP flooding: This attack involves flooding the system with many HTTP requests. This can exhaust system resources, such as CPU and memory, and cause the system to crash or become unresponsive.
3. SYN flooding: This type of attack involves flooding the system with a large number of SYN packets. This can exhaust system resources, such as CPU and memory, and cause the system to crash or become unresponsive.

A Distributed Denial of Service (DDoS) attack on a Linux-based home router flooded the router's CPU and memory with many packets, causing it to crash and become unresponsive. This attack was discovered in 2018 and affected many home routers that use Embedded Linux.

Malware?Attack

A type of software designed to perform malicious actions on a computer or network. Malware attacks on embedded Linux systems can occur in several ways, including viruses, trojans, worms, and other types of malicious software. Some well-known and documented attacks have:

"Linux.Wifatch," a worm that targeted embedded Linux devices, was discovered in 2014 and is specifically designed to infect IoT devices running embedded Linux. Once installed, the worm could gain unauthorized access to the device, steal sensitive information, or perform other malicious actions.

A trojan known as "Linux/Ebury," targeted Linux systems were discovered in 2011 and designed to infect Linux servers. Once installed, the trojan can gain unauthorized access to the server, steal sensitive information, or perform other malicious actions.

A malware family known as Mirai primarily targets IoT devices running embedded Linux, and it was first discovered in 2016. Once installed, it can be used to gain unauthorized access to the device, steal sensitive information, or perform other malicious actions.

Physical attacks?

Any attempt to physically access the embedded system and tamper with it. This can include a wide range of activities, such as:

1. Tampering with hardware components: This can include opening the device to access internal features, such as memory, storage, or processors, and modifying or replacing them with malicious components.
2. Connecting to the system's serial console can allow an attacker to access the system's command line interface and execute arbitrary commands or code.
3. Attempting to boot the system from an external device can allow an attacker to bypass the system's built-in security mechanisms and gain access to the system's firmware or operating system.
4. Side-channel attacks: This type of attack involves extracting sensitive information from the?embedded system by measuring its physical properties, such as power consumption, electromagnetic radiation, or sound.
5. Supply chain attacks occur when a malicious actor attacks an embedded device during manufacturing or when it's shipped.

Detection and Prevention

Recognizing and preventing such attacks can be accomplished through a combination of technical and non-technical strategies.

Technical strategies include the following practices:

1. Deploying firewalls, intrusion detection systems, antivirus and anti-malware software, and other security tools to prevent and detect attacks. Keeping these tools and software updated with the latest security patches.
2. Regularly monitoring system logs: Monitoring system logs can help detect unusual or malicious activity, such as unauthorized access attempts or changes to system files.
3. Implementing security best practices: This includes implementing secure coding practices, hardening the system's configuration, and implementing secure protocols and encryption for network communication.
4. Regularly updating the system: Keeping the system up-to-date with the latest security patches can help prevent known vulnerabilities from being exploited by attackers.
5. Physical security: Implementing physical security controls, such as tamper-evident seals, can help prevent physical tampering with the system.
6. Implementing a secure boot process: A secure boot process can help ensure that only authorized software is running on the system, and it prevents the execution of malicious code during the boot process.
7. Conducting penetration testing: Regular penetration testing can help identify vulnerabilities in the system and areas that need improvement.

It's important to note that security is a continuous process, and it's essential to regularly review and update the security controls to ensure that they effectively detect and prevent attacks on embedded Linux systems.

Non-technical strategy refers to the administrative, organizational, and management practices used to protect an organization's information and technology assets. These could include:

1. Security policies and procedures: Having clear and well-defined security policies and procedures in place can help ensure that employees and other stakeholders understand their roles and responsibilities in protecting the organization's information and technology assets.
2. Risk management: Identifying and assessing potential risks to the organization's information and technology assets can help develop security policies and procedures and implement technical and non-technical controls.
3. Employee training and awareness: Providing employees with training and awareness on security best practices and the risks associated with different types of security threats can help ensure they can effectively protect the organization's information and technology assets.
4. Incident response plan: A well-defined incident response plan can help ensure the organization is prepared to respond to and recover from security incidents effectively.
5. Access controls: Implementing access controls, such as authentication and authorization, can help ensure that only authorized individuals can access the organization's information and technology assets.
6. Third-party management: Ensuring that third-party vendors and service providers with access to the organization's information and technology assets comply with the organization's security policies and procedures.
7. Compliance: Ensuring that the organization is compliant with relevant laws, regulations, and industry standards can help ensure that the organization's information and technology assets are protected.
8. Regular Audit: Regularly auditing the organization's information and technology assets, including the security controls in place, can help identify vulnerabilities and areas that need to be improved.

All listed policies must be an integral part of the overall security strategy, as they help establish the framework for the protection of the systems and provide a way to measure the effectiveness of the technical controls.

summary

Embedded Linux systems are widely used in critical infrastructures such as industrial control systems, home routers, IoT devices, and many others. However, these systems are not immune to security threats and attacks. This article provides an overview of the various episodes embedded Linux systems are vulnerable to. Attacks can have serious consequences, including financial loss, reputational damage, and loss of sensitive information. Organizations must have incident response plans and regularly train employees on best practices to strengthen defenses against threats.