This could have been prevented if the shell functions of PHP were disabled so that arbitrary shell commands cannot be executed from PHP.Ī web shell is usually installed by taking advantage of vulnerabilities present in the web server's software. The following is a simple example of a web shell written in PHP that executes and outputs the result of a shell command: Remote file inclusion (RFI) and local file inclusion (LFI) vulnerabilities Īn attacker may also modify ( spoof) the Content-Type header to be sent by the attacker in a file upload to bypass improper file validation (validation using MIME type sent by the client), which will result in a successful upload of the attacker's shell.limiting the file types that can be uploaded File processing and uploading vulnerabilities, which can be mitigated by e.g.web server software such as NGINX or content management system applications such as WordPress) Vulnerabilities in applications and services (e.g.Web shells are installed through vulnerabilities in web application or weak server security configuration including the following: To use as command and control base, for example as a bot in a botnet system or in way to compromise the security of additional external networks.To relay commands inside the network which is inaccessible over the Internet.Launch distributed denial-of-service ( DDoS) attacks.Website defacement by modifying files with a malicious intent.Infecting website visitors ( watering hole attacks).Web shells are used in attacks mostly because they are multi-purpose and difficult to detect.

Īn attacker can use a web shell to issue shell commands, perform privilege escalation on the web server, and the ability to upload, delete, download, and execute files to and from the web server. These vulnerabilities are often present in applications that are run on a web server. Using network monitoring tools, an attacker can find vulnerabilities that can potentially allow delivery of a web shell. However, Active Server Pages, ASP.NET, Python, Perl, Ruby, and Unix shell scripts are also used, although these languages are less commonly used. Web shells are most commonly written in the PHP programming language due to the widespread usage of PHP for web applications. Ī web shell could be programmed in any programming language that is supported on a server. A web shell is unique in that a web browser is used to interact with it.

Security information and event management (SIEM)Ī web shell is a shell-like interface that enables a web server to be remotely accessed, often for the purposes of cyberattacks.

Host-based intrusion detection system (HIDS).

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