Like Unix systems, Linux implements a multi-user environment where users are granted specific privileges and there is some form of access control implemented. To gain control over a Linux system or to cause any serious consequences to the system itself, the malware would have to gain root access to the system.[2]
In the past, it has been suggested that Linux had so little malware because its low market share made it a less profitable target. Rick Moen, an experienced Linux system administrator, counters that:
[That argument] ignores Unix's dominance in a number of non-desktop specialties, including Web servers and scientific workstations. A virus/trojan/worm author who successfully targeted specifically Apache httpd Linux/x86 Web servers would both have an extremely target-rich environment and instantly earn lasting fame, and yet it doesn't happen.[3]
In 2008 the quantity of malware targeting Linux was noted as increasing. Shane Coursen, a senior technical consultant with Kaspersky Lab, said at the time, "The growth in Linux malware is simply due to its increasing popularity, particularly as a desktop operating system... The use of an operating system is directly correlated to the interest by the malware writers to develop malware for that OS."[4]
Tom Ferris, a researcher with Security Protocols, commented on one of Kaspersky's reports, stating, "In people's minds, if it's non-Windows, it's secure, and that's not the case. They think nobody writes malware for Linux or Mac OS X. But that's not necessarily true."[4]
Some Linux users do run Linux-based anti-virus software to scan insecure documents and email which comes from or is going to Windows users. SecurityFocus's Scott Granneman stated:
...some Linux machines definitely need anti-virus software. Samba or NFS servers, for instance, may store documents in undocumented, vulnerable Microsoft formats, such as Word and Excel, that contain and propagate viruses. Linux mail servers should run AV software in order to neutralize viruses before they show up in the mailboxes of Outlook and Outlook Express users.[1]
Because they are predominantly used on mail servers which may send mail to computers running other operating systems, Linux virus scanners generally use definitions for, and scan for, all known viruses for all computer platforms. For example, the open source ClamAV "Detects ... viruses, worms and trojans, including Microsoft Office macro viruses, mobile malware, and other threats."[5]
Cases of malware intended for Microsoft Windows systems posing a danger to Linux systems when run through compatibility layers such as Wine, while uncommon, have been recorded.[6]
Viruses and trojan horses
The viruses listed below pose a potential, although minimal, threat to Linux systems. If an infected binary containing one of the viruses were run, the system would be temporarily infected, as the Linux kernel is memory resident and read-only. Any infection level would depend on which user with what privileges ran the binary. A binary run under the root account would be able to infect the entire system. Privilege escalation vulnerabilities may permit malware running under a limited account to infect the entire system.
It is worth noting that this is true for any malicious program that is run without special steps taken to limit its privileges. It is trivial to add a code snippet to any program that a user may download and let this additional code download a modified login server, an open mail relay, or similar program, and make this additional component run any time the user logs in. No special malware writing skills are needed for this. Special skill may be needed for tricking the user to run the (trojan) program in the first place.
The use of software repositories significantly reduces any threat of installation of malware, as the software repositories are checked by maintainers, who try to ensure that their repository is malware-free. Subsequently, to ensure safe distribution of the software, checksums are made available. These make it possible to reveal modified versions that may have been introduced by e.g. hijacking of communications using a man-in-the-middle attack or via a redirection attack such as ARP or DNS poisoning. Careful use of these digital signatures provides an additional line of defense, which limits the scope of attacks to include only the original authors, package and release maintainers and possibly others with suitable administrative access, depending on how the keys and checksums are handled. Reproducible builds can ensure that digitally signed source code has been reliably transformed into a binary application.
Worms and targeted attacks
The classical threat to Unix-like systems are vulnerabilities in network daemons, such as SSH and web servers. These can be used by worms or for attacks against specific targets. As servers are patched quite quickly when a vulnerability is found, there have been only a few widespread worms of this kind. As specific targets can be attacked through a vulnerability that is not publicly known there is no guarantee that a certain installation is secure. Also servers without such vulnerabilities can be successfully attacked through weak passwords.
Web scripts
Linux servers may also be used by malware without any attack against the system itself, where e.g. web content and scripts are insufficiently restricted or checked and used by malware to attack visitors. Some attacks use complicated malware to attack Linux servers, but when most get full root access then hackers are able to attack by[7] modifying anything like replacing binaries or injecting modules. This may allow the redirection of users to different content on the web.[8] Typically, a CGI script meant for leaving comments, could, by mistake, allow inclusion of code exploiting vulnerabilities in the web browser.
Buffer overruns
Older Linux distributions were relatively sensitive to buffer overflow attacks: if the program did not care about the size of the buffer itself, the kernel provided only limited protection, allowing an attacker to execute arbitrary code under the rights of the vulnerable application under attack. Programs that gain root access even when launched by a non-root user (via the setuid bit) were particularly attractive to attack. However, as of 2009 most of the kernels include address space layout randomization (ASLR), enhanced memory protection and other extensions making such attacks much more difficult to arrange.
Cross-platform viruses
An area of concern identified in 2007 is that of cross-platform viruses, driven by the popularity of cross-platform applications. This was brought to the forefront of malware awareness by the distribution of an OpenOffice.org virus called Badbunny.
What makes this virus worth mentioning is that it illustrates how easily scripting platforms, extensibility, plug-ins, ActiveX, etc, can be abused. All too often, this is forgotten in the pursuit to match features with another vendor... The ability for malware to survive in a cross-platform, cross-application environment has particular relevance as more and more malware is pushed out via Web sites. How long until someone uses something like this to drop a JavaScript infecter on a Web server, regardless of platform?[9]
Social engineering
As is the case with any operating system, Linux is vulnerable to malware that tricks the user into installing it through social engineering. In December 2009 a malicious waterfall screensaver that contained a script that used the infected Linux PC in denial-of-service attacks was discovered.[10]
Go-written malware
The IBM Security Report: Attacks on Industries Supporting COVID-19 Response Efforts Double had as a key point that "Cybercriminals Accelerate Use of Linux Malware – With a 40% increase in Linux-related malware families in the past year, and a 500% increase in Go-written malware in the first six months of 2020, attackers are accelerating a migration to Linux malware, that can more easily run on various platforms, including cloud environments." That these cybercriminals are increasingly using Linux and Unix to target hospitals and allied industries (that rely on these systems and cloud networks) that they are increasingly vulnerable during the COVID-19 crisis, such as the Red Cross cyberattack.[11]
There are a number of anti-virus applications available which will run under the Linux operating system. Most of these applications are looking for exploits which could affect users of Microsoft Windows.
For Microsoft Windows-specific threats
These applications are useful for computers (typically, servers) which will pass on files to Microsoft Windows users. They do not look for Linux-specific threats.
The following is a partial list of known Linux malware. However, few if any are in the wild, and most have been rendered obsolete by Linux updates or were never a threat. Known malware is not the only or even the most important threat: new malware or attacks directed to specific sites can use vulnerabilities previously unknown to the community or unused by malware.
Mirai (malware) – a DDoS botnet spreads through telnet service and designed to infect Internet of Things (IoT).[42][43][44][45]
GafGyt/BASHLITE/Qbot – a DDoS botnet spreads through SSH and Telnet service weak passwords, firstly discovered during bash Shellshock vulnerability.[46]
LuaBot – a botnet coded with modules component in Lua programming language, cross-compiled in C wrapper with LibC, it aims for Internet of Things in ARM, MIPS and PPC architectures, with the usage to DDoS, spreads Mirai (malware) or selling proxy access to the cyber crime.[47][48]
Hydra,[49] Aidra,[50] LightAidra[51] and NewAidra[52] – another form of a powerful IRC botnet that infects Linux boxes.
EnergyMech 2.8 overkill mod (Linux/Overkill) – a long-lasting botnet worm designed to infect servers with its bot and operated through IRC protocol, for the purposes of DDoSing and spreading itself.[53]
Xor DDoS[69] – a trojan malware that hijacks Linux systems and uses them to launch DDoS attacks which have reached loads of 150+ Gbps.[70]
Hummingbad – has infected over 10 million Android operating systems. User details are sold and adverts are tapped on without the user's knowledge thereby generating fraudulent advertising revenue.[71]
NyaDrop – a small Linux backdoor compiled from a Linux shellcode to be used to infect Linux boxes with bigger size Linux malware.[72]
PNScan – Linux trojan designed to aim routers and self-infecting to a specific targeted network segment in a worm-like form[73]
SpeakUp – a backdoor trojan that infects six different Linux distributions and macOS devices.[74]
Malware is any software intentionally designed to cause disruption to a computer, server, client, or computer network, leak private information, gain unauthorized access to information or systems, deprive access to information, or which unknowingly interferes with the user's computer security and privacy. Researchers tend to classify malware into one or more sub-types.
In computing, a Trojan horse is any malware that misleads users of its true intent by disguising itself as a standard program. The term is derived from the ancient Greek story of the deceptive Trojan Horse that led to the fall of the city of Troy.
This timeline of computer viruses and worms presents a chronological timeline of noteworthy computer viruses, computer worms, Trojan horses, similar malware, related research and events.
A botnet is a group of Internet-connected devices, each of which runs one or more bots. Botnets can be used to perform distributed denial-of-service (DDoS) attacks, steal data, send spam, and allow the attacker to access the device and its connection. The owner can control the botnet using command and control (C&C) software. The word "botnet" is a portmanteau of the words "robot" and "network". The term is usually used with a negative or malicious connotation.
ESET NOD32 Antivirus, commonly known as NOD32, is an antivirus software package made by the Slovak company ESET. ESET NOD32 Antivirus is sold in two editions, Home Edition and Business Edition. The Business Edition packages add ESET Remote Administrator allowing for server deployment and management, mirroring of threat signature database updates and the ability to install on Microsoft Windows Server operating systems.
Mobile malware is malicious software that targets mobile phones or wireless-enabled Personal digital assistants (PDA), by causing the collapse of the system and loss or leakage of confidential information. As wireless phones and PDA networks have become more and more common and have grown in complexity, it has become increasingly difficult to ensure their safety and security against electronic attacks in the form of viruses or other malware.
The Storm Worm is a phishing backdoor Trojan horse that affects computers using Microsoft operating systems, discovered on January 17, 2007. The worm is also known as:
The Storm botnet or Storm Worm botnet was a remotely controlled network of "zombie" computers that had been linked by the Storm Worm, a Trojan horse spread through e-mail spam. At its height in September 2007, the Storm botnet was running on anywhere from 1 million to 50 million computer systems, and accounted for 8% of all malware on Microsoft Windows computers. It was first identified around January 2007, having been distributed by email with subjects such as "230 dead as storm batters Europe," giving it its well-known name. The botnet began to decline in late 2007, and by mid-2008 had been reduced to infecting about 85,000 computers, far less than it had infected a year earlier.
Man-in-the-browser, a form of Internet threat related to man-in-the-middle (MITM), is a proxy Trojan horse that infects a web browser by taking advantage of vulnerabilities in browser security to modify web pages, modify transaction content or insert additional transactions, all in a covert fashion invisible to both the user and host web application. A MitB attack will be successful irrespective of whether security mechanisms such as SSL/PKI and/or two- or three-factor authentication solutions are in place. A MitB attack may be countered by using out-of-band transaction verification, although SMS verification can be defeated by man-in-the-mobile (MitMo) malware infection on the mobile phone. Trojans may be detected and removed by antivirus software, but a 2011 report concluded that additional measures on top of antivirus software were needed.
Koobface is a network worm that attacks Microsoft Windows, Mac OS X, and Linux platforms. This worm originally targeted users of networking websites such as Facebook, Skype, Yahoo Messenger, and email websites such as GMail, Yahoo Mail, and AOL Mail. It also targets other networking websites, such as MySpace, Twitter, and it can infect other devices on the same local network. Technical support scammers also fraudulently claim to their intended victims that they have a Koobface infection on their computer by using fake popups and using built-in Windows programs.
Clampi is a strain of computer malware which infects Windows computers. More specifically, as a man-in-the-browser banking trojan designed to transmit financial and personal information from a compromised computer to a third party for potential financial gain as well as report on computer configuration, communicate with a central server, and act as downloader for other malware. Clampi was first observed in 2007 affecting computers running the Microsoft Windows operating system.
Alureon is a trojan and rootkit created to steal data by intercepting a system's network traffic and searching for banking usernames and passwords, credit card data, PayPal information, social security numbers, and other sensitive user data. Following a series of customer complaints, Microsoft determined that Alureon caused a wave of BSoDs on some 32-bit Microsoft Windows systems. The update, MS10-015, triggered these crashes by breaking assumptions made by the malware author(s).
The Bredolab botnet, also known by its alias Oficla, was a Russian botnet mostly involved in viral e-mail spam. Before the botnet was eventually dismantled in November 2010 through the seizure of its command and control servers, it was estimated to consist of millions of zombie computers.
OSX.FlashBack, also known as the Flashback Trojan, Fakeflash, or Trojan BackDoor.Flashback, is a Trojan horse affecting personal computer systems running Mac OS X. The first variant of Flashback was discovered by antivirus company Intego in September 2011.
Virut is a cybercrime malware botnet, operating at least since 2006, and one of the major botnets and malware distributors on the Internet. In January 2013, its operations were disrupted by the Polish organization Naukowa i Akademicka Sieć Komputerowa.
Dorkbot is a family of malware worms that spreads through instant messaging, USB drives, websites or social media channels like Facebook. It originated in 2015 and infected systems were variously used to send spam, participate in DDoS attacks, or harvest users' credentials.
Mirai is malware that turns networked devices running Linux into remotely controlled bots that can be used as part of a botnet in large-scale network attacks. It primarily targets online consumer devices such as IP cameras and home routers. The Mirai botnet was first found in August 2016 by MalwareMustDie, a white hat malware research group, and has been used in some of the largest and most disruptive distributed denial of service (DDoS) attacks, including an attack on 20 September 2016 on computer security journalist Brian Krebs' website, an attack on French web host OVH, and the October 2016 DDoS attacks on Dyn. According to a chat log between Anna-senpai and Robert Coelho, Mirai was named after the 2011 TV anime series Mirai Nikki.
MalwareMustDie, NPO is a whitehat security research workgroup that was launched in August 2012. MalwareMustDie is a registered nonprofit organization as a medium for IT professionals and security researchers gathered to form a work flow to reduce malware infection in the internet. The group is known for their malware analysis blog. They have a list of Linux malware research and botnet analysis that they have completed. The team communicates information about malware in general and advocates for better detection for Linux malware.
Trojan.Win32.DNSChanger is a backdoor trojan that redirects users to various malicious websites through the means of altering the DNS settings of a victim's computer. The malware strain was first discovered by Microsoft Malware Protection Center on December 7, 2006 and later detected by McAfee Labs on April 19, 2009.
Trickbot was a trojan for Microsoft Windows and other operating systems. Its major function was originally the theft of banking details and other credentials, but its operators have extended its capabilities to create a complete modular malware ecosystem.
↑ njccic (28 December 2016). "Mirai Botnet". The New Jersey Cybersecurity and Communications Integration Cell (NJCCIC). Archived from the original on 12 December 2016. Retrieved 28 December 2016.
↑ de Almeida Lopes, Anthony (July 2007). "Project Bukowski". Archived from the original on 14 May 2013. Retrieved 8 March 2008.
↑ herm1t (February 2008). "Caveat virus". Archived from the original on 23 December 2018. Retrieved 17 January 2010.{{cite web}}: CS1 maint: numeric names: authors list (link)
↑ herm1t (October 2007). "Hashin' the elves". Archived from the original on 10 October 2014. Retrieved 17 January 2010.{{cite web}}: CS1 maint: numeric names: authors list (link)
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