# Command Injection (CWE-78)

User input is passed unsanitized to system shell commands, allowing attackers to execute arbitrary commands on the server.

- Prevalence: Common Found in many applications
- Impact: Critical Full server compromise
- Prevention: Avoid shell Use execFile, not exec

**OWASP:** Injection (A03:2021-Injection) - #3

## Description

This could allow attackers to execute unexpected, dangerous commands directly on the operating system. This weakness can lead to a vulnerability in environments in which the attacker does not have direct access to the operating system.

## Prevention

Prevention strategies for OS Command Injection based on 3 Shoulder detection rules.

### Go

Use exec.Command with explicit arguments, never shell invocation

### Node.js

Use execFile/spawn with array arguments instead of exec with string commands

### Python

Use subprocess.run with list arguments and shell=False

## Warning Signs

- [CRITICAL] user input flowing to os/exec command execution, enabling OS command injection
- [CRITICAL] user input flowing to shell command execution functions
- [CRITICAL] untrusted user input flowing into operating system command execution
functions without proper saniti

## Consequences

- Execute Unauthorized Commands
- Read Application Data
- Bypass Protection Mechanism

## Mitigations

- Use library calls rather than external processes
- If using Runtime.exec(), use the version that takes an array of arguments
- Use structured mechanisms that automatically enforce separation between data and code

## Detection

- Total rules: 3
- Critical: 3
- Languages: go, javascript, typescript, python

## Rules by Language

### Go (1 rules)

- **Command Injection via os/exec** [CRITICAL]: Detects user input flowing to os/exec command execution, enabling OS command injection.
  - Remediation: Use exec.Command with explicit arguments and validate input against an allowlist.

```go
allowed := map[string]bool{"file1.txt": true, "file2.txt": true}
if !allowed[userInput] {
    return errors.New("not allowed")
}
cmd := exec.Command("cat", userInput)
```

Learn more: https://shoulder.dev/learn/go/cwe-78/command-injection

### Javascript (1 rules)

- **Command Injection via child_process** [CRITICAL]: Detects user input flowing to shell command execution functions.
  - Remediation: Use execFile() with argument arrays instead of exec() with string commands.

```javascript
const { execFile } = require('child_process');
execFile('ls', ['-la', directory]);
```

Learn more: https://shoulder.dev/learn/javascript/cwe-78/command-injection

### Typescript (1 rules)

- **Command Injection via child_process** [CRITICAL]: Detects user input flowing to shell command execution functions.
  - Remediation: Use execFile() with argument arrays instead of exec() with string commands.

```javascript
const { execFile } = require('child_process');
execFile('ls', ['-la', directory]);
```

Learn more: https://shoulder.dev/learn/javascript/cwe-78/command-injection

### Python (1 rules)

- **OS Command Injection** [CRITICAL]: Detects untrusted user input flowing into operating system command execution
functions without proper sanitization.
  - Remediation: Use subprocess with argument lists and shell=False.

```python
subprocess.run(["ping", "-c", "2", ip_address], check=True)
```

Learn more: https://shoulder.dev/learn/python/cwe-78/command-injection