Web shell definition
A web shell is a program or a script that allows someone to gain access to a web server or website. Web shells are mostly used by cybercriminals. It is called a “shell” because the script has a command-line interface (similar to a shell on a computer).
Before hackers can install a web shell, they need to penetrate a system or network. Once they’ve installed a web shell, it acts as a backdoor into the targeted system. The hacker can execute commands, manipulate files, and perform several other actions without the website owner’s knowledge.
See also: backdoor
How web shells work
- Establishing access. The hacker finds a vulnerability in a website or web server (e.g., a weak password, outdated software, or a flaw in the website’s code).
- Installing a web shell. After identifying the vulnerability, the attacker finds a way to exploit it to gain access to the server. They upload and install a web shell script to the website, often by injecting malicious code into a vulnerable file or exploiting a file upload functionality.
- Execution. Once the web shell is uploaded, the attacker can access it through a web browser. The hacker can control the website through a command-line interface, similar to a shell on a computer.
- Command execution. The attacker executes commands on the compromised website. They can perform various malicious actions, such as manipulating browsing directories and files, running scripts, or interacting with databases.
- Backdoor access. To maintain access to the system, the hacker may modify the server’s configuration files or create additional backdoors.
- Malicious actions. Once the hacker gains complete control of the website, they can cause serious damage, such as stealing sensitive data, defacing the website, and launching further attacks.
How to prevent web shell attacks
- Regularly update software
- Perform file integrity monitoring
- Use web application firewalls
- Ensure the website code is secure
- Use strong authentication
- Regularly review and analyze server logs.