Web Shells

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🌐 Web Shells — Overview & Use

🧾 What is a Web Shell?

• A Web Shell is a browser-based shell session that allows interaction with the underlying OS of a web server.

• Provides Remote Code Execution (RCE) via a browser interface.

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⚙️ How Web Shells Work:

1. 🔍 Find a vulnerability in a web application (e.g., file upload flaw).

2. 📤 Upload a payload (written in web server’s supported language, like PHP, ASP, JSP).

3. 🌐 Access the uploaded payload through the browser.

4. 🧠 Execute OS commands via the web interface.

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🛠️ Common Web Shell Payloads:

• Written in PHP, ASP, JSP, etc.

• Examples:

  • php-reverse-shell.php

  • Simple PHP shell:

    <?php echo shell_exec($_GET['cmd']); ?>

    Access it in a browser like:

    http://target.com/uploads/shell.php?cmd=whoami

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🧩 Use Cases

• Initial access point to execute basic commands.

• Useful when:

  • You can’t get a reverse shell yet.

  • You’re limited to HTTP-based communication.

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⚠️ Limitations of Web Shells:

• ❌ Unstable / Unreliable:

  • Some servers delete uploaded files after a time.

  • Web shells may crash or get blocked.

• ❌ Limited interaction:

  • No proper TTY (terminal), no tab-completion, etc.

• ❌ Can be noisy:

  • Security tools may detect it.

• 🕵️ Relying on it for long-term access is not advised.

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🧱 Best Practice: Upgrade to a Reverse Shell

• Use the web shell to download or execute a reverse shell payload.

• Establish a reverse shell for:

  • More stable interaction

  • TTY spawning

  • Scripting and automation

• Reverse shell tools: nc, bash, perl, python, msfvenom, etc.