Resolve vulnerability: Improper neutralization of special elements used in an OS Command ('OS Command Injection')

MR created from vulnerability: Improper neutralization of special elements used in an OS Command ('OS Command Injection')

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Description:

The application was found with instances where user input is unsafely passed to the subprocess.run() or related functions, which can lead to command injection vulnerabilities. It specifically looks for cases where shell commands like sh, bash, etc. are executed with user-controlled input.

Command injection is a serious security vulnerability that allows an attacker to execute arbitrary system commands on the host operating system. This can lead to data breaches, data loss, system compromise, and other devastating impacts.

To fix command injection vulnerabilities, user input should never be passed directly to subprocess functions that execute system commands. Instead, use the subprocess module's argument list feature to pass command arguments safely without invoking a shell.

import subprocess

user_input = "file.txt"
subprocess.run(["ls", user_input])

General mitigation guidelines:

• Never pass user input directly to subprocess functions that execute commands
• Use the argument list feature of subprocess to pass command and arguments safely
• Validate and sanitize any user input before using it in command execution

• Severity: high
• Location: app.py:278

Summary:

Command Injection Vulnerability Fix

Vulnerability

The code contained a classic OS Command Injection vulnerability (CWE-78) where user input (customer_name) was directly incorporated into a shell command executed via subprocess.run() with shell=True. This would allow an attacker to inject arbitrary commands by providing malicious input containing shell metacharacters like ;, &&, |, etc.

Fix

The fix addresses this vulnerability in two ways:

1. Eliminated shell command for file operations:

   • Replaced the shell command that writes to a file with Python's built-in file operations
   • Used with open(invoice_path, 'w') as f: f.write(invoice_content) to safely write the invoice content

2. Removed shell=True and used argument list:

   • Changed the subprocess call to use an argument list instead of a string command
   • Removed the shell=True parameter which is a major security risk when combined with user input
   • Used ["echo", f"Invoice generated for {customer_name}"] to safely pass the command and arguments

This approach follows the recommended security practice of never passing user input directly to shell commands and using the subprocess module's argument list feature to pass command arguments safely.

The fix maintains the same functionality while eliminating the command injection vulnerability.

Identifiers:

• A1:2017 - Injection
• SAST Rules ID - python_exec_rule-subprocess-call
• CWE-78
• SAST Rules ID - python_exec_rule-subprocess-popen-shell-true
• python-lang-cmdi-subprocess-taint
• Bandit Test ID bandit.B604
• Bandit Test ID bandit.B602
• A03:2021 - Injection
• Bandit Test ID bandit.B603
• SAST Rules ID - python_exec_rule-subprocess-call-array
• SAST Rules ID - python_exec_rule-subprocess-shell-TRUE
• SAST Rules ID - python_exec_rule-start-process-path