Linux Malware: Common Types & How to Stay Safe

Linux is known for its robust security features: it’s open source, powerful, and gives you a lot of room to experiment. Sadly, even Linux isn’t immune to malware attacks.

The reality is that no system is entirely immune to threats. A growing concern for Linux users is the rise of malicious software (or malware) specifically designed to target Linux-based systems. That’s why understanding malware protection for Linux has become essential. In this guide, we’ll help you identify the biggest malware threats you can run into and how to protect yourself against them, including getting a VPN for Linux.

Common Types of Linux Malware

Let’s first start with what Linux malware is. In simple terms, it’s the collective name for various types of malicious software that target Linux operating systems. It can range from ransomware to botnets, to cryptojacking malware with malicious purposes like data theft, file encryption, or system disruption. Linux malware exploits system vulnerabilities, and primary delivery mechanisms include email attachments, infected software downloads, compromised websites, and weak network security protocols.

We’ve seen a significant rise in Linux malware in recent years, with the highly evasive SYMBIOTE shared object (SO) library that executes privilege escalation attacks being one of the worst of the bunch. Let’s look at the different types of Linux malware first and discuss how to spot them before getting into fending them off. 

Linux Malware Targeting Linux Devices

Linux malware comes in various forms, each with a unique MO. Here are some of the most common types that target your Linux system:

1. Trojans 

One of the most common types of Linux malware is the Trojan horse. Named after the mythological wooden horse used by the Greeks to infiltrate Troy, Trojan horses disguise themselves as legitimate software or files, tricking you into unknowingly installing them. Once inside your system, Trojan horses can perform a variety of malicious activities, such as stealing your sensitive information, modifying files, or even taking control of your system.

1. Worms

Worms can cause significant damage to your system. Unlike viruses that require user interaction to spread, worms are self-replicating programs that can spread across networks without user input. Once a worm infects your Linux system, it can consume system resources, slow down your network performance, and even infiltrate your other connected devices.

1. Botnets

Botnets are networks of infected computers controlled by a central command and control (C&C) server. They’re often used to carry out large-scale attacks, such as distributed denial of service (DDoS) attacks or spam distribution. Your Linux system can become part of a botnet if it’s infected with malware that lets an attacker control it remotely. IoT devices (including those you use at home) with poorly configured network security protocols are especially susceptible to becoming part of botnets.

Cybercriminals can exploit a router, security camera, or any other connected Linux device in your home with malware to take over these devices. They then use your devices to help launch various cyber attacks. These botnets are a popular option for DDoS attacks; like the Mirai botnet, which launched one of the biggest DDoS attacks in the past decade at Dyn, a major DNS provider. The attack used devices like printers, smart TVs, and even baby monitors as part of its botnet.

Another popular use of a router botnet is to run a proxy server on infected routers. The proxy lets cybercriminals conceal their activity by using and hiding behind your IP address. Both of these services are in high demand in cybercrime, and botnet operators often infect networks and then sell them to cybercriminals.

1. Ransomware

Ransomware has become a major concern for Linux users in recent years. This type of malware encrypts your files or locks you out of your system, demanding a ransom payment in exchange for restoring access. Ransomware attacks can have devastating consequences, leading to data loss, financial loss, and even reputational damage.

1. NAS Ransomware

Remember the days when your computer would get hijacked, and the attackers would ask you to fork over a few hundred bucks in ransom just to get your files back? That threat is back but with a twist: Now, cybercriminals are targeting your home file servers and NAS devices, too.

This type of ransomware targets your operating system by either guessing weak passwords or exploiting vulnerabilities in the software installed on your NAS devices. Once inside, the ransomware encrypts files stored on your NAS, making them inaccessible to you until you’ve given in to the attacker’s demands.

1. Rootkits

Rootkits are a particularly insidious type of Linux malware that can go undetected for long periods. These malicious programs are designed to gain root access to your Linux system, giving the attacker complete control over your device and the ability to hide their presence. Rootkits often exploit vulnerabilities in the operating system or other software to gain access and can be extremely difficult to detect and remove.

1. Cryptojackers

Cryptojackers are a modern breed of cybercriminals capitalizing on the cryptocurrency boom. They use sneaky software to mine cryptocurrencies on your device without your consent, a practice known as cryptojacking. Cryptojackers exploit your devices’ processing power to mine coins like Bitcoin or Monero for personal gain by infecting your machine, smart devices, or networks with malware that runs in the background. 

Cryptojacking’s popularity stems from its low risk and ease of execution compared to traditional cybercrimes, making it an attractive option for bad actors.

Understanding Linux Malware Attacks 

Linux systems, while generally considered more secure than popular counterparts, are increasingly targeted by malware. In fact, some reports suggest Linux-based ransomware attack attempts surged by over 60%  in recent years. These attacks use various tactics to infiltrate your system. As an example, some malware is designed for specific targets while others are let loose to see who takes the bait (also known as the spray-and-pray technique). Let’s look at the more common elements of many types of Linux malware attacks:

• Delivery: The malware sneaks onto your system through email attachments, compromised sites, infected downloads, or exploited vulnerabilities in your connection or software.
• Execution: Once inside, the malware runs its malicious code. The code’s purpose and function depend on the specific malware and its creator’s goals.
• Privilege Escalation (Optional): Some malware types attempt to gain higher-level permissions (like root access) to your system. This gives the attacker greater control and the ability to cause more damage, and it also makes the malware harder to detect or remove.
• Propagation (Optional): Certain malware strains aim to spread across the local network to other vulnerable systems it can find. Attackers do this hoping to find more valuable data to use or hold for ransom, or to add more devices to their botnet.
• Malicious Activity: This is where the malware’s intended purpose comes into play.  Expect data theft, file encryption, unexplained changes to your files or software, account password changes, or devices becoming slow with spikes in data usage.
• Concealment: Malware attacks are typically crafty, using techniques like rootkits or mimicking legitimate system processes to hide their presence.
• Communication with C&C: Most types of malware connect to a C&C (or C2) server run by the attacker. This lets attackers send updates, issue new commands, and extract stolen data.

Are there any warning signs you can look for that may indicate you’re under attack? Yes, and we’ll look at them next. 

How Do You Spot a Linux Malware Attack?

Detecting Linux malware can be challenging as malware developers are getting exceptionally good at hiding their tracks. That said, some subtle signs that may indicate a malware infection on your Linux system are easier to spot if you know what to look for. Just be careful to not instantly assume your system is compromised when you notice any of these signs. A hardware or software issue may be the real culprit and not a malicious attacker bent on ruining your day.

Unusual Network Activity

If you notice unusual network traffic, high bandwidth consumption without any legitimate reason, or unexpected connections to unknown IP addresses, it’s time to investigate further. Keep an eye on your network logs and monitor any suspicious activity. An increase in outbound connections or data transfers could indicate that your system has been compromised.

Slow Performance

Is your computer suddenly running slower than usual? Are you experiencing frequent crashes or freezes? These could be signs that malware has infiltrated your system. Malware can interfere with essential system functions or programs, causing crashes or freezes as the system struggles to cope. It can also consume system resources like processing power and memory, leaving less for other programs to run smoothly. This may make your device’s responses feel sluggish compared to what you’re used to. So, if your Linux system runs significantly slower than usual, it’s worth investigating further.

Unexpected Pop-Ups or Ads

If you start seeing an excessive number of pop-ups or ads, even on websites you don’t normally see them on, it could be a sign of an adware infection. Adware is a type of malware that displays unwanted advertisements. It can be intrusive and may disrupt your browsing experience. More importantly, it can also be a way for attackers to steal your personal information or redirect you to malicious websites.

Unexplained Changes

If you notice unauthorized changes to your system settings, files, or programs, it’s essential to investigate the cause. Pay attention to any strange files or directories that have appeared out of nowhere. Malware often disguises itself in unsuspecting locations, so keep an eye out for anything unusual.

If you suspect your Linux device is infected with malware, you should take immediate action to prevent further damage to your system and data. We’ve got some tips on how to deal with an attack next. 

Responding to Malware Attacks on Linux

Your Linux systems can become targets for malware attacks, despite your best efforts. If you suspect your device is infected, follow these steps:

• Isolate the Affected System: Disconnect the infected device from the network to prevent the malware from spreading to other devices.
• Assess the Damage: Determine the extent of the infection. Identify any compromised files, unauthorized access, or other signs of the attack.
• Contain the Malware: Quarantine and analyze any suspicious files to understand the nature of the malware. This information can help in its removal and future prevention.
• Remove the Malware: Use reputable antivirus software or seek professional help to remove the malware from your Linux system. Ensure you follow the recommended removal procedures. 
• Restore from Backups: If possible, restore your Linux system from a clean backup to eliminate any remnants of the malware.
• Update Security Measures: After recovering from a malware attack, review and update your security measures to prevent future infections. Learn from the attack and implement additional preventive measures if necessary. For example, installing a VPN on your Linux, if you don’t have one, is a good option to improve your security arsenal. 

PIA’s Linux VPN encrypts your data in transit, shielding it from malware designed to steal information or exploit vulnerabilities. Our network has servers in 91+ countries, helping you strengthen your system’s defenses without sacrificing your online freedom. PIA’s built-in ad blocker, MACE, adds another layer of protection by blocking ads, trackers, and malicious domains.

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Overcoming Vulnerabilities in Linux Security: Best Practices

At this point, you’re probably wondering how to protect your Linux devices from malicious hackers. First, adopt a proactive security strategy. Keep yourself updated on the latest threats and consistently seek ways to enhance your Linux system’s security. Don’t forget about your IoT devices either. Remember, prevention is your strongest defense against malware. 

Here are ten best practices you can follow to better protect your Linux devices against potential malware attacks:

1. Change your admin passwords and device names for your router and IoT devices; don’t rely on default settings. Most manufacturers use the same default name and password for a range of devices, meaning criminals can easily guess these credentials. Cybercriminals exploit this by scanning for open ports and using lists of common logins to brute-force their way in.
2. Create strong, long passwords (think sentences rather than single words) and use unique passwords for every account. This practice enhances your security by reducing the risk of cybercriminals using your compromised password to get into multiple devices or accounts.
3. Use antimalware programs to protect against viruses, Trojans, and spyware. Make sure to regularly update the antivirus software and run scans to detect and prevent potential threats. PIA has an antivirus add-on that continuously scans your PC for malware, providing real-time protection against online attacks.
4. Implement security measures such as firewalls, ad blockers, whitelisting trusted applications, a sandbox, improved email security, and a zero-trust policy to prevent ransomware attacks.
5. Isolate sensitive parts of your network to reduce the chances of cybercriminals getting into your system through network vulnerabilities. Also, regularly perform vulnerability assessments to check for any weak spots in your system that attackers might exploit.
6. Limit cloud functionality for your home devices. If you don’t use the cloud functions of your NAS (such as WD My Cloud) or can do without them, it’s best to disable them completely and only access your NAS internally through your local network. This won’t just reduce your attack surface but will also protect you from incidents like data breaches on the manufacturer’s side.
7. NAS devices, routers, and even smart doorbells are like small servers. They come with extra features like hosting media, accessing files through FTP, connecting printers to home computers, and controlling them with commands through SSH. Only turn on the features you actually use to limit the attack surface on your network.
8. One of the most effective security measures you can adopt is to keep your Linux systems and software up-to-date. Regularly check for and apply updates to benefit from the latest security patches and improvements. For your home devices, regularly update the firmware for your router, NAS, and other devices.
9. Implement Security-Enhanced Linux (SELinux) to enhance your control over system access. SELinux is a mandatory access control system that restricts access beyond what traditional Linux permissions offer. This prevents malicious actors from easily gaining admin control over any system processes.
10. Regular penetration testing can help identify potential vulnerabilities in your system before attackers can exploit them. This proactive approach lets you address issues before they can be used against you.
11. Get a VPN to encrypt your traffic and mask your IP address. It makes it more difficult for attackers to intercept your data or track your online activity. A VPN can help protect against potential Linux malware attacks by securing your connection against Man-in-the-Middle attacks, cookie hijacking, SSL stripping, and unsecured public Wi-Fi networks.

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Final Thoughts on Linux Security 

Linux malware is a significant threat to Linux-based systems. It can steal your data, disrupt operations, or encrypt your files for ransom. To defend against these threats, it’s crucial to stay proactive and follow best practices. From updating your software to setting up strong passwords, every individual step strengthens your whole system’s security.

Investing in tools like an antimalware program and a reliable VPN for Linux adds an extra layer of protection that helps safeguard your system’s security and your privacy. By staying informed and taking preventive measures, you can effectively mitigate the risk of a Linux malware infection.

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