> For the complete documentation index, see [llms.txt](https://nuclei-av.gitbook.io/malware-handbook/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://nuclei-av.gitbook.io/malware-handbook/malware-analysis/malware-analysis-methodologies/analyzing-aspx-webshells.md).

# Analyzing ASPX Webshells

**Overview of Webshells**

* **Webshell**: A web interface allowing remote access to a web server. It typically includes features for file management, program execution, and command execution on the server.
* Webshells appear as a webpage and allow command execution via input boxes, but the underlying code is not visible when accessed through a browser.

**Steps for Analysis**

1. **Setting Up IIS for Analysis**:
   * **Enable IIS**:
     * Go to Control Panel > Windows Features, or type "Windows Features" from the Start menu.
     * Check the **Internet Information Services (IIS)** box, expand it, and select the most recent version of **ASP.NET**.
   * **Start IIS**:
     * Open **IIS Manager** from the Start menu.
     * Right-click on the server name, select **Start** if needed.
     * Expand to **Default Website**, right-click, select **Manage Website** > **Start**.
     * Right-click on **Default Web Site**, select **Explore** to open the web server folder.
2. **Deploying and Accessing the Webshell**:
   * Copy **re\_webshell.aspx** into the IIS web server folder.
   * Open an internet browser and navigate to:

     ```arduino
     arduinoCopy codehttp://localhost/re_webshell.aspx
     ```
   * The webshell allows command execution. For example:
     * **`/c dir c:\Users`** displays user profiles.
     * **`whoami`** displays the web server username.
3. **Analyzing Webshell Code**:
   * Open **re\_webshell.aspx** in **Notepad++**.
   * The code is split into HTML (for forms) and a script containing the `execCmd` function.
   * The `execCmd` function handles input commands using `.NET classes` such as `Process`, `ProcessStartInfo`, and `StreamReader`.
4. **Using Abyss Web Server as an Alternative**:
   * **Install Abyss Web Server**:
     * Configure it to avoid conflicts with FakeNet.
     * Access configuration via system tray icon > **Restore** > **Hosts** > **Default Host** > **Configure**.
   * **Deploy Webshell**:
     * Copy **re\_webshell.aspx** to the **HTDocs** folder in the Abyss installation directory.
     * Configure ASP.NET in Abyss Web Server.
   * **Access Webshell**:
     * Open an internet browser and navigate to:

       ```bash
       bashCopy codehttp://localhost:8000/aspfiles/re_webshell.aspx
       ```
5. **Debugging with Visual Studio**:
   * **Setup Visual Studio**:
     * Create a new **ASP.NET Web Application** project.
     * Add **re\_webshell.aspx** to the project.
   * **Debugging**:
     * Set a breakpoint in the `execCmd` function.
     * Run the application and interact with the webshell to hit the breakpoint.
     * Monitor variable values and step through the code in Visual Studio.

**Summary**

* **Webshells**: Allow remote command execution via a web interface.
* **Tools**: IIS, Abyss Web Server, Visual Studio.
* **Key Steps**: Set up the web server, deploy the webshell, analyze code, and debug if necessary.

This process helps in understanding and analyzing ASPX webshells to uncover their functionalities and potential impacts on the server.