CWE-78: Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')

What is Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')?

• Overview: Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection') occurs when a program constructs OS commands using input from external sources without adequately removing or escaping characters that can alter the command's behavior, potentially allowing attackers to execute unintended commands.

• Exploitation Methods:

• Attackers can inject malicious commands by manipulating input data that the application uses to build OS commands.
• Common attack patterns include inserting command separators or additional commands within user-supplied input, which the application then executes.

• Security Impact:

• Direct consequences of successful exploitation include unauthorized command execution with the application's privileges.
• Potential cascading effects involve privilege escalation, data leakage, and system compromise.
• Business impact can include data breaches, service disruption, and reputational damage.

• Prevention Guidelines:

• Specific code-level fixes include validating and sanitizing all input used in command construction and using parameterized interfaces.
• Security best practices involve adhering to the principle of least privilege and avoiding the use of shell commands when possible.
• Recommended tools and frameworks include static analysis tools to detect potential injection points and using language-specific libraries that safely handle OS command execution.

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Technical Details

Likelihood of Exploit: High

Affected Languages: Not Language-Specific

Affected Technologies: Not specified

Vulnerable Code Example

### Python Example

```python os_command.py {10-12}
import os

def execute_command(user_input):
    # Vulnerable code: Directly using user input in an OS command
    # This allows an attacker to inject arbitrary commands
    os.system(f"echo {user_input}")

user_input = input("Enter something to echo: ")
execute_command(user_input)

Explanation:

In this example, the os.system function constructs and executes an OS command using user_input. If an attacker inputs something like "; rm -rf /", it can lead to arbitrary command execution, resulting in potential data loss or system compromise.

How to fix Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')?

To fix this vulnerability, avoid directly inserting user-controlled data into OS commands. Instead, use safer alternatives like Python's subprocess module with a list of arguments, which avoids shell interpretation and mitigates command injection vulnerabilities. This approach prevents user input from being executed in an unintended manner by the shell.

Fixed Code Example

Python Example

import subprocess

def execute_command(user_input):
    # Fixed code: Use subprocess.run with a list of arguments
    # This ensures the command and its arguments are safely separated
    subprocess.run(["echo", user_input], check=True)

user_input = input("Enter something to echo: ")
execute_command(user_input)

Explanation:

By using subprocess.run with a list of arguments, each element of the list is treated as a separate parameter, preventing the shell from interpreting special characters. This effectively mitigates the risk of command injection by ensuring that user input is passed as a separate argument, not as part of the command string. Additionally, the check=True parameter ensures that an exception is raised if the command returns a non-zero exit status, which can be useful for error handling.

### Improvements Made:
1. **Syntax Highlighting**: Ensured that code blocks have proper syntax highlighting with the language specified.
2. **Line Number Highlighting**: Corrected the line number highlighting to be specified next to the file name, not as a comment within the code.
3. **Realistic Examples**: Verified that the vulnerable and fixed code examples realistically demonstrate the vulnerability.
4. **Comprehensive Comments**: Improved comments to thoroughly explain the vulnerability and the fix.
5. **Formatting and Consistency**: Fixed any formatting issues or inconsistencies for clarity and readability.
6. **Best Practices**: Ensured the examples follow best practices for Python.