What is a backdoor
A backdoor is amalware typethat negates normal authentication procedures to access a system. As a result, remote access is granted to resources within an application, such as databases and file servers, giving perpetrators the ability to remotely issue system commands and update malware.
Backdoor installation is achieved by taking advantage of vulnerable components in a web application. Once installed, detection is difficult as files tend to be highly obfuscated.
Webserver backdoors are used for a number of malicious activities, including:
Backdoor trojan installation
The most prevalent backdoor installation method involvesremote file inclusion(RFI), an attack vector that exploits vulnerabilities within applications that dynamically reference external scripts. In an RFI scenario, the referencing function is tricked into downloading a backdoor trojan from a remote host.
Example of a backdoor dashboard with command execute capabilities.
Perpetrators typically identify targets using scanners, which locate websites having unpatched or outdated components that enable file injection. A successful scanner then abuses the vulnerability to install the backdoor on the underlying server. Once installed, it can be accessed at any time, even if the vulnerability enabling its injection has since been patched.
Backdoor trojan injection is often done in a two-step process to bypass security rules preventing the upload of files above a certain size. The first phase involves installation of a dropper—a small file whose sole function is to retrieve a bigger file from a remote location. It initiates the second phase—the downloading and installation of the backdoor script on the server.
The challenge of backdoor shell removal
Once installed, backdoors are very hard to weed out. Traditionally, detection involves using software scanners to search for known malware signatures in a server file system. This process is error prone, however. Backdoor shell files are almost always masked through the use of alias names and—more significantly—code obfuscation (sometimes evenmultiple layers of encryption).
Detection is further complicated since many applications are built on external frameworks that use third-party plugins; these are sometimes laden with vulnerabilities or built-in backdoors. Scanners that rely on heuristic and signature-based rules might not be able to detect hidden code in such frameworks.
Even if a backdoor is detected, typical mitigation methods (or even a system reinstallation) are unlikely to remove it from an application. This is particularly true for backdoors having a persistent presence in rewritable memory.
See how Imperva Web Application Firewall can help you with backdoor attacks.
Mitigating backdoor shell attacks with Imperva
At Imperva, we use a combination of methods to prevent backdoor installation, as well as to detect and quarantine existing backdoor shells.
On one hand, the Imperva cloudweb application firewall(WAF) uses a combination of default and user-defined security rules to prevent RFI attacks from compromising your application. The WAF is deployed as a secure proxy at the edge of your network, ensuring that malicious requests are blocked before they’re able to interact with your application. As a result, your site is secured from the moment you onboard our service.
If your webserver was already compromised before onboarding, the Impervabackdoor protection solutionlets you detect and remove shells from your file system.
The solution takes the novel approach of intercepting connection requests to malicious shells—a preferable alternative to scanning a server for backdoor files. Unlike backdoor files, which are easily hidden, connection requests cannot be obfuscated to hide their malicious intent.
https://youtu.be/fnVCUDitolY
By tracing back such communication attempts, the Imperva cloud service can identify any backdoor shell, even if its source code was encrypted to avoid scanners.
FAQs
A backdoor is a malware type that negates normal authentication procedures to access a system. As a result, remote access is granted to resources within an application, such as databases and file servers, giving perpetrators the ability to remotely issue system commands and update malware.
What is a Trojan backdoor attack? ›
Backdoor Trojans are malicious software programs designed to grant unwanted access for a remote attack. Remote attackers can send commands or leverage full control over a compromised computer.
What is an example of a backdoor attack? ›
PoisonTap is a well-known example of backdoor attack. In this, hackers used malware to gain root-level access to any website, including those protected with 2FA. WordPress was spotted with multiple backdoors in 2014. These backdoors were WordPress plug-ins featuring an obfuscated JavaScript code.
What is Trojan backdoor activity? ›
* Backdoor. Trojan - a Trojan with a primary purpose of opening a back door to allow remote access at a later time. * Downloader - a Trojan with a primary goal of downloading another piece of software, usually additional malware.
Can a backdoor be removed? ›
Backdoors are dangerous, run in stealth mode, and are almost impossible to manually detect. But, they must be removed. It is highly recommended that computer users adopt automatic system removal methods. In addition, strong firewalls and updated antivirus software must be in place.
What is an example of a Trojan attack? ›
For example, a user might receive an email from someone they know, which includes an attachment that also looks legitimate. However, the attachment contains malicious code that executes and installs the Trojan on their device.
What is the most common backdoor? ›
The most prevalent backdoor installation method involves remote file inclusion (RFI), an attack vector that exploits vulnerabilities within applications that dynamically reference external scripts. In an RFI scenario, the referencing function is tricked into downloading a backdoor trojan from a remote host.
What does a backdoor look like? ›
Backdoors can look like normal php code or obfuscated (intentionally obscured to make code ambiguous) and hidden. A backdoor can be inserted into a valid file as only one short line of code that looks rather innocent.
Which type of malware creates a backdoor? ›
Backdoor malware is generally classified as a Trojan. A Trojan is a malicious computer program pretending to be something it's not for the purposes of delivering malware, stealing data, or opening up a backdoor on your system.
Is spyware a backdoor? ›
Backdoor attacks often involve the use of spyware or malware. Spyware, a type of malicious software, is designed to gather sensitive information without the user's knowledge or consent. It can monitor keystrokes, capture screenshots, access personal data, and even record audio or video.
Trojan-Spy programs can spy on how you're using your computer - for example, by tracking the data you enter via your keyboard, taking screen shots, or getting a list of running applications.
How do I get rid of Trojan virus? ›
Installing and using a trusted antivirus solution is also one of the top ways to get rid of trojans. An effective antivirus program searches for valid trust and app behavior, as well as trojan signatures in files in order to detect, isolate and then promptly remove them.
Can a Trojan virus record you? ›
Trojan-Spy programs can spy on how you're using your computer – for example, by tracking the data you enter via your keyboard, taking screenshots or getting a list of running applications.
What are the signs of a backdoor? ›
Signs of backdoor attacks
Unusual network traffic: Observe any unexpected or unexplained network traffic, especially if it's coming from or going to unfamiliar IP addresses or domains. Backdoors often communicate with command-and-control servers, generating suspicious network activity.
Are backdoors illegal? ›
Let's say a developer uses a backdoor on a website they worked on simply to access the files in an unapproved manner. Even if they do not cause any damage to the system or files, the developer could face fines of $5,000 and up to five years in prison.
What is the purpose of a backdoor? ›
How do backdoors work? In the context of an attack, backdoors are hidden mechanisms attackers use to access a system without authentication. However, vendors sometimes create backdoors for legitimate purposes, such as restoring a user's lost password or providing government entities with access to encrypted data.
How are backdoors detected? ›
Scan for malware and trojans: Backdoor attacks often involve installing malicious software on compromised systems, such as trojans or other malware. Conduct a thorough scan of your systems using reliable anti-malware programs to identify and remove unauthorised programs or files.
What is Trojan virus and how do you remove it? ›
Trojan viruses can be removed in various ways. If you know which software contains the malware, you can simply uninstall it. However, the most effective way to remove all traces of a Trojan virus is to install antivirus software capable of detecting and removing Trojans.
What does getting backdoored mean? ›
1. adjective [ADJ n] You can use backdoor to describe an action or process if you disapprove of it because you think it has been done in a secret, indirect, or dishonest way. [disapproval] Firms are using the program as a backdoor way to replace domestic employees with cheaper labor.
What is the difference between Trojan horses and backdoors? ›
Unlike viruses, trojan horses do not replicate themselves, but they can be just as destructive. Trojans also open a backdoor entry to your computer, giving command to malicious actor or allowing malicious users/programs access to your system. This leads to confidential and personal information being stolen.
