Command Injection: Exploiting System Commands for Unauthorized Access

Introduction to Command Injection link

Command Injection is a serious web security vulnerability that allows attackers to execute arbitrary operating system commands on the server hosting the application. This vulnerability occurs when an application takes user-supplied input and passes it directly to a system shell without proper sanitization.

How Command Injection Works link

1. The attacker provides malicious input: The attacker inserts special characters or commands that are interpreted by the operating system’s shell.
2. The application executes a system command: The vulnerable application, without proper validation, incorporates the user input into a system command.
3. The shell executes the attacker’s commands: The operating system’s shell interprets the attacker’s injected commands and executes them with the privileges of the application.
4. The attacker gains control or access to sensitive information: The attacker can potentially gain unauthorized access to the server, execute malicious code, steal sensitive data, or disrupt the application’s functionality.

Common Command Injection Techniques link

• Using Semicolons or Ampersands: Attackers can use characters like ; or & to chain multiple commands together. For example, command1; command2 will execute command1 and then command2.
• Using Pipes: Attackers can use the pipe character | to redirect the output of one command to the input of another. For example, command1 | command2 will execute command1 and pipe its output to command2.
• Using Backticks or Dollar Signs: Attackers can use backticks () or dollar signs (`$()`) to execute commands within a command. For example, `command1 `command2 will execute command2 and substitute its output into command1.

Practical Example: Exploiting Command Injection in a Diagnostic Tool link

Imagine a web application with a diagnostic tool that allows administrators to ping a specified IP address. The application might use a system command like this:

  ping -c 4 user_supplied_ip_address
  

An attacker could inject the following input:

  127.0.0.1; cat /etc/passwd
  

This would result in the following command being executed:

  ping -c 4 127.0.0.1; cat /etc/passwd
  

The application would first ping the localhost address and then execute the cat /etc/passwd command, potentially revealing sensitive user information.

Detecting Command Injection Vulnerabilities link

• Analyze Application Functionality: Identify functionalities that involve executing system commands based on user input.
• Test with Suspicious Inputs: Submit inputs containing special characters like ;, &, |, ``, or $() to see if the application executes unintended commands.
• Inspect Server Logs: Monitor server logs for unusual command executions or unexpected output.
• Use Vulnerability Scanners: Employ automated vulnerability scanners that can detect command injection vulnerabilities.

Conclusion link

Command Injection is a severe security vulnerability that can grant attackers significant control over the server. By understanding how command injection attacks work and implementing effective prevention measures, developers can protect their applications and infrastructure from this threat.