What is a Web Shell Attack and How to Prevent It?

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Web shell attacks are a significant threat to online security, with attackers using malicious scripts to take control of servers and manipulate websites. These stealthy attacks can be difficult to detect, which is why it’s important to understand them and protect against them effectively.

In this comprehensive guide, we will look at the nature of web shell attacks , how they work, look at the different types, provide real-world examples, and show you how to prevent a web shell attack.

Table of contents

What is a Web Shell Attack?
How do web shell attacks work?
Types of web shells
Examples of web shell attacks
Why are web shell attacks used?
How to detect Web Shell attacks?
How to block Web Shell injections?
What is a Web Shell Attack?
A web shell attack is a cyber attack in which an attacker exploits vulnerabilities in a website or web application to upload a malicious script (known as a “web shell”) to the server. This web shell allows the attacker to access and control the affected website or server.

In cybersecurity, a “shell” refers to a command-line interface that allows users to interact with a computer or server by entering commands. The term “web shell” is a combination of the words “web” (referring to communication with web servers) and “shell” (referring to the functionality of the command-line interface).

This attack works under the guise of seemingly mobile app development service legitimate server-side scripts. You may still be unaware that these scripts are hiding on your system, giving the hacker unrestricted access. Web shell attacks allow the attacker to freely navigate your web-accessible directories, manipulate files, and even create a backdoor for future exploits.

Cybercriminals create web shell attacks in a language that the target web servers can interpret, such as PHP, ASP, JSP, or even Perl. This ensures that these scripts are difficult to detect and can bypass security systems. Web shells can target both local servers and Internet-facing servers.




How do web shell attacks work?
Imagine you have a web application running on your server. An attacker discovers a vulnerability, perhaps an unsanitized input field or outdated software. Using this weakness, they upload a malicious script disguised as a harmless file. This script runs on your server and gives the attacker the ability to execute commands remotely.

Once installed, the web shell allows the attacker to manipulate your server. They can execute commands, steal sensitive data , or even use your server as a launching pad for further attacks. The scale of damage is enormous – from data theft and website corruption to complete server takeover.

The stealthy nature of web shells makes them particularly dangerous. They can remain dormant, making them difficult to detect. An attacker can also modify a web shell's script to bypass standard security measures.

They aim to maintain long-term access, ensuring that the web shell remains undetected. They can periodically update the script or change its location to bypass security controls.

Types of web shells
Now let's go over the different types of web shells. This knowledge will help you anticipate potential vulnerabilities and develop more robust defense strategies.