What is Backdoor Virus?
January 04, 2024
A backdoor is any method that allows unauthorized remote access to your device, often without your knowledge or consent. Cybercriminals, government officials, or IT professionals may install a backdoor on your device using various techniques, including malware or exploiting vulnerabilities in your software or hardware/microware.
Once infiltrated, these parties can leverage backdoors for various purposes, such as surveillance, sabotage, data theft, cryptojacking, or launching malware attacks.
Backdoor Trojan Detection Challenges
Detecting a backdoor poses challenges since it can remain inactive for extended periods, and victims might not be aware of its presence. Even if detected, victims often struggle to determine the culprit or identify stolen information. Backdoors share similarities with remote administration tools and Trojans, but their increased complexity and danger warrant a separate category.
Antivirus products may categorize some backdoors as Trojans while overlooking others. The key factor is not functionality but the installation order and visibility in the system. Unlike full-fledged remote administration utilities that display dialogs and graphical reflections during installation, backdoors operate silently and inconspicuously.
While active, backdoors remain hidden – not appearing in the taskbar, system tray, or the list of active processes. In contrast, legitimate administrators often have visible indicators, such as icons or entries in system processes. Additionally, full-fledged products provide an uninstall function, visible in the list of installed applications, while removing a backdoor may require specialized software or a meticulous approach.
Examples of Backdoor Virus Attacks in 2024:
- XZ Utils Backdoor Discovered, Threating Linux Servers
- BianLian Exploits TeamCity Vulnerability to Deploy Backdoors
- LitterDrifter - Russia’s USB Worm Targeting Ukrainian Entities
- Mirai variant "Pandora" infects Android TV for DDoS attacks.
- Gozi and IcedID Trojans Spread via Malvertising
- FIN8 Updated Sardonic Backdoor to Deliver Noberus Ransomware
- Trojanized TeamViewer Installer Spreads njRAT
- TeamTNT Group Returns with Silent Bob Campaign
Classification of Backdoor Viruses
Backdoors can infiltrate two crucial parts of your system - software and hardware. Let's delve into each option for a more comprehensive understanding:
1. Hardware/Firmware
These involve physical modifications that enable remote access to your device. Manufacturers may introduce hardware-type malicious objects, also known as hardware implants, during the production stages. These backdoors, not detectable by code scans or antivirus software, cannot be removed through software updates or replacements.
2. Software
Typically, these are malicious files that meticulously conceal their presence to prevent your operating system from detecting unauthorized access. While software backdoors can be introduced during manufacturing (known as software implants), more commonly, users unwittingly allow their entry.
Backdoors also vary in their methods of implementation, including:
1. Hardware Backdoors
This category encompasses modified computer chips or other firmware/hardware allowing uncontrolled access to a device. Examples include phones, IoT devices (thermostats, home security systems), routers, and computers. Hardware backdoors may transmit user data, provide remote access, or facilitate surveillance. They can be shipped with products (illegally or for nefarious purposes) or physically installed if a device is stolen.
2. Cryptographic Backdoors
A cryptographic backdoor functions as a "master key," unlocking all encrypted data using a specific encryption protocol. While encryption standards like AES rely on end-to-end encryption, cryptographic backdoors manipulate the mathematical complexities of a protocol, providing external users access to encrypted data exchanged between parties.
3. Backdoor Trojans
Trojans are malicious files posing as legitimate ones to gain access to your device. Once acquiring necessary permissions, Trojans can install themselves and potentially allow attackers to access your files or introduce more severe malware onto your device.
Backdoor Examples
| Backdoor name | Description |
|---|---|
| Smokeloader | Infamous backdoor known for its detection evasion capabilities. |
| DBatLoader | Novice malware designed for two purposes - remote access provision and malware delivery. |
| Cobalt Strike | Designed as a penetration testing toolkit, Cobalt Strike was highly appreciated by threat actors. |
4. Remote-access trojans
Remote-access trojans, or shortly RATs, are specific backdoor-like malicious programs that aim at providing remote access to the infected machine and a range of other capabilities. Contrary to “classic” backdoors, RATs have wider remote access options and can also include spyware-like features, like data stealing or keylogging. One may say, RAT trade stealthiness and swiftness of execution for more wide and flexible functionality.
RAT Examples
| RAT name | Description |
|---|---|
| DarkCrystal RAT | Novice RAT that boasts the ability to manipulate software and hardware of the infected system. |
| njRAT | Old-timer among RATs that runs since 2012. Can be configured to suit each specific attack case. |
| Loda RAT | Classic RAT that offers remote access and stealer functionality. It can also deliver other malware. |
| LimeRAT | The example of an open-source RAT. Offers functionality similar to njRAT - extended remote connection + spyware capabilities. |
5. Rootkits
Rootkits are more advanced malicious programs capable of hiding their activities from the operating system, with the operating system granting them security privileges (root access). Rootkits can allow attackers to remotely access your device, modify files, monitor your activity, and harm your system. Rootkits can take the form of both software and physically changed computer chips.
Once in the system, backdoors give the attacker the needed data and allow him to control the machine. This can happen in three ways:
- BindShell - the malware waits for an external connection;
- Back Connect - the backdoor connects to the cybercriminal's computer itself;
- Middle Connect - data is exchanged between the cybercriminal and his tool using an additional server.
What Are the Goals of Backdoors
The target audience of backdoors is similar to that of other malware. Typically, attackers focus on devices owned by commercial organizations, government agencies, enterprises, etc. However, even the computers of ordinary users are not immune. Due to their elusive nature, backdoors can persist on a system for extended periods (months or even years), enabling hackers to monitor victims, steal data, and employ compromised devices for various malicious activities.
Once access to the system is obtained, hackers can meticulously study the user's identity and exploit this information for criminal purposes. This could involve stealing sensitive documents, developments, or trade secrets, which might be used by company competitors or sold in appropriate places. Notably, a concerning aspect of backdoors is their potential to be as harmful as the payloads they deploy. Regardless of their primary task, cybercriminals may delete all files on the victim's machine or even format the hard drives entirely.
Sources of Threat
A backdoor in a system can emerge either through legitimate software (including the operating system) or unintentional vulnerabilities. Individuals with physical access to a computer can also install a backdoor. Occasionally, developers intentionally leave backdoors for remote technical support. However, more commonly, cybercriminals or intrusive governments install backdoors to gain unauthorized access to the victim's device.
In some instances, an unsuspecting PC user may unknowingly install a backdoor from an email attachment or alongside downloaded files from a file-sharing service. Fraudsters disguise the infection with suggestive names and texts, enticing the victim to open or run the infected object. Additionally, software backdoors can be introduced into a computer by other malware, silently spreading through the information system without triggering warnings or dialog boxes that might raise the user's suspicion, much like worms.
How to Prevent Backdoor Attacks?
Unfortunately, no one is immune to backdoor attacks. Hackers are constantly improving techniques and creating more sophisticated malicious files to gain access to user devices. However, by following the instructions below, you can reduce the risk of a successful backdoor infection:
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Close Unused Network Ports
An open port on your network can receive traffic from remote locations, creating a potential weak point. Hackers usually target unused ports, allowing them to install backdoors that gain access to your device. No software will alert you to the intrusion. However, this isn't a problem for most home users since home router ports are closed by default. Small business owners should exercise caution when opening ports.
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Use Strong Passwords
An insecure or default password is a green light for hackers to access your accounts. Once they crack one account, they can easily access your other accounts and devices. This is how hackers used the Mirai botnet in 2016, affecting 2.5 million IoT devices worldwide. It was designed to scan the Internet for IoT devices with unchanged default passwords, then hack into those devices and enslave them with a botnet. We recommend using only strong passwords and enabling MFA to protect your accounts from unauthorized access.
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Keep Your Software Up-to-date
Hackers can exploit vulnerabilities to install malware on users' devices. Installing updates for your operating system may cause some discomfort, but it helps developers fix vulnerabilities, reducing the risk of backdoors appearing on the system.
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Download Files with Caution
Most malware attacks are caused by users. If you download a free program that usually costs money or download the latest Marvel movie via torrent and suddenly install a malicious file, your system becomes vulnerable. When downloading any file from the Internet, check if you're only getting the file you need or if you're also getting malware as a bonus. Even if the file behaves like the one you're looking for, it could be a trojan. Always download files from official websites and avoid pirate sites.
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Use a Firewall and Antivirus
Always use advanced antivirus software along with a firewall. This can detect and prevent malware, including trojans, cryptojackers, spyware, and rootkits. A firewall is essential for backdoor protection because it monitors your device's incoming and outgoing traffic. If someone outside your network tries to access your device, the firewall will block them. Antivirus can detect backdoor viruses and neutralize them before they can infect your computer.
