What is a Web Shell?
A web shell is a browser-based shell session we can use to interact with the underlying operating system of a web server. Again, to gain remote code execution via web shell, we must first find a website or web application vulnerability that can give us file upload capabilities. Most web shells are gained by uploading a payload written in a web language on the target server. The payload(s) we upload should give us remote code execution capability within the browser.
Laudanum, One Webshell to Rule Them All
Laudanum is a repository of ready-made files that can be used to inject onto a victim and receive back access via a reverse shell, run commands on the victim host right from the browser, and more. The repo includes injectable files for many different web application languages to include asp, aspx, jsp, php, and more
The Laudanum files can be found in the /usr/share/laudanum directory.
https://github.com/jbarcia/Web-Shells/tree/master/laudanum
Antak Webshell
Antak is a web shell built in ASP.Net included within the Nishang project. Nishang is an Offensive PowerShell toolset that can provide options for any portion of your pentest. Antak utilizes PowerShell to interact with the host, making it great for acquiring a web shell on a Windows server. The UI is even themed like PowerShell. It's time to dive in and experiment with Antak.
The Antak files can be found in the /usr/share/nishang/Antak-WebShell directory.
$ cp /usr/share/nishang/Antak-WebShell/antak.aspx /home/administrator/Upload.aspx
Make sure you set credentials for access to the web shell. Modify line 14, adding a user (green arrow) and password (orange arrow). This comes into play when you browse to your web shell, much like Laudanum
PHP Web Shells