In today’s cybersecurity climate, chances are you’ve heard of ‘backdoors’ and the grave challenge they present to your company’s network. In broad terms, a backdoor is a way for hackers to establish unauthorized access to a network from a remote location.
Backdoors provide hackers with a hidden entrance to a network and are usually undetectable by security systems because they don’t leave any special traces behind. That means that once a hacker uses a backdoor to get into your network, it is hard for traditional security tools like malware scanners to detect any suspicious behavior.
Backdoors can be used to steal sensitive company information, install various types of malware (e.g. spyware, ransomware), and even launch cyberattacks from computers within your network. In this blog post, we explore the different ways hackers infiltrate a network to install a backdoor and what you and your company or organization can do to protect against backdoor attacks.
How Hackers Gain Access To The Network
In order for a remote hacker to successfully implant a backdoor, a hacker must first find a compromised system or a weak point in the system. Typically, hackers will search for vulnerabilities and weaknesses within a network using specialized software. This type of software may include network scanning tools, which are already used by security administrators to assess a system. For security specialists, network scanning tools are regarded as a key component in maintaining secure networks and systems. However, the downside is that hackers may use this tool for malicious purposes.
Remote hackers use various network scanning and techniques to discover active hosts, ports, services, and operating systems with vulnerabilities. Hence, attackers typically scan networks from Layers 2 to 7. Given these parameters, what are the weak points that remote hackers can exploit to install a backdoor?
> Weak passwords
As expected, weak passwords are the top of the list for ways in which hackers can gain access to your company network. Many outdated computer systems continue to use the default network settings — including usernames and passwords. This also holds true for firewalls, routers, or wireless access points and can provide an entry for hackers too. Hackers can also stumble upon unused, or forgotten accounts (i.e a former employee’s account) and can easily password if they are set to their default settings. Hackers can also use brute force to “crack” passwords or use phishing techniques to steal passwords to access accounts on the network.
> Accounts with system or admin privileges
After a hacker successfully exploits a system, he or she will want to make sure they can easily get back inside the network at a later time. One way to do this is to create new user accounts with system privileges.
As mentioned, hackers usually get inside the system using the weak credentials of user accounts or guest accounts. If a hacker can find an unused account with system privileges, they’ve hit the jackpot. This can be dangerous for many reasons especially if a hacker gains full access to an account with a wide range of system privileges.
For example, admin accounts may have access to port scanning tools to capture network traffic and find vulnerabilities within a network and to protecting against these potential threats. However, hackers can also use them to spy on the network, exploit the vulnerabilities found in the network, and create backdoors.
> Open ports
An open port is a port on the network that accepts incoming packets from remote locations. As a result, it has the potential to be exploited by hackers. In fact, a common way for hackers to create a backdoor is by opening up a port on the target’s machine and installing an agent/program to listen in on that port. In order to get inside the network, hackers will typically use an obscure port that is not already in use. Furthermore, because more and more companies are scanning for TCP ports and not for open UDP ports, many attackers are now using UDP ports to hide and create backdoors. Because hackers may be worried about a system administrator discovering their open port during a routine scan of the system, hackers can create special backdoors. These types of backdoors remain shut until the hacker carries out an “open sesame” command for the backdoor to open the port and for the hacker to enter undetected.
> Trojans
A Trojan horse or simply a Trojan is a type of malware disguised as legitimate software to gain access to users’ systems including the network. Certain Trojans can steal sensitive company data and gain backdoor access to the network once activated.
One example of a backdoor is Tini which targets Windows systems. This program, though not originally intended to be used as a Trojan, is used by hackers to create a backdoor. Tini allows attackers to gain unauthorized access to the target computer.
Tini listens at TCP port 7777 and so once a hacker connects, they gain access to a remote command prompt. This allows hackers to remotely control a computer without any validation or authentication. With the backdoor installed, the hacker can remotely access a system whenever they like.
Backdoor Trojans are often used to unite a group of victim computers to form a botnet or zombie network that can be used for criminal purposes.
> Web shells
Sometimes, hackers may use legitimate web applications to launch an attack from a target network/system or edit, delete, and download files on a website. This can be accomplished with a shell backdoor. Web shells are pieces of malicious code and can be written in any server-supported languages including PHP, .NET, Python, Ruby, etc.). They can either be “self-sufficient,” meaning they contain a wide range of functionalities or require C&C (command and control) functions. A backdoor shell that is uploaded to a site can allow hackers to gain access to files stored on that site and therefore functions as a RAT variant or backdoor Trojan.
Hackers also create web shells containing backdoor functionality via SQL injection and remote file inclusion (RFI) attacks on vulnerable web applications.
A Caveat About Backdoors
Because backdoors are largely undetectable, once a hacker is inside the network, their main goal is to gain repeated access to a network. As exemplified above, using a Trojan can also permit hackers to remotely access a system at a later time. These examples of backdoors are meant to remove traces of a hacker’s initial entry from system logs.
Hackers may also conceal their malicious activities by changing the system logs. In fact, many hackers evade detection by hiding files deep in system directories using file names that are not “suspicious” to a systems administrator. Usually, by the time a system administrator reviews the system logs, the new system gots unnoticed and so the hacker remains hidden.
What You Can Do About Remote Access Hacking
Backdoors are dangerous for many reasons, and for companies and organizations, they can lead to major data leakage, data theft, complete website defacement, and other irreversible damage.
We’ve just outlined the many ways hackers use weak points in a system to create a backdoor for remote access hacking. Preventing malicious actors from entering the network in the first place is crucial.
Once an unauthorized user enters a network, it is near impossible to track their behavior once inside. It makes sense, then, for companies and organizations to detect any suspicious activity prior to their point of entry.
Of course, security tools can help in deterring hackers from exploiting weak points. For example, firewalls can restrict or permit a specific kind of traffic to enter through the firewall and have the ability to open and close ports. Because changing firewall settings inadvertently deals with network security, only system administrators should make these changes.
Vulnerabilities in web applications also pose serious risks for companies and organizations. As mentioned, hackers can use web shells on vulnerable web applications to create backdoors, and hence firewalls must be able to provide adequate protection against cyberattacks like SQL injection.
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