How Denial of Service via Infinite Loop happens in Node.js dependencies and how to fix it

Introduction

In the app_store application, a high-severity vulnerability was discovered lurking in the dependency tree. The nanoid package—a popular library for generating unique, URL-friendly IDs—contained a critical flaw in its customAlphabet function that could send your Node.js application into an infinite loop. This isn't a theoretical risk; CVE-2026-67213 affects any application using nanoid versions before 3.3.17 (for the 3.x branch) or 5.1.6 (for the 5.x branch).

The vulnerability was flagged in app_store/package-lock.json, where nanoid version 3.3.16 was locked as a transitive dependency. While the assessment indicated the vulnerability was "present in dependency tree, not confirmed reachable," the high severity rating and potential for complete service disruption made this a priority fix.

The Vulnerability Explained

What is nanoid?

Nanoid is a tiny, secure, URL-friendly unique string ID generator for JavaScript. It's commonly used for generating session IDs, database keys, and other identifiers. The library includes a customAlphabet function that allows developers to create ID generators with custom character sets.

The Infinite Loop Problem

The vulnerability exists in the customAlphabet function of nanoid versions before 3.3.17 and 5.1.6. Under specific conditions involving the custom alphabet configuration, the function's internal loop can fail to reach its exit condition, causing the application to hang indefinitely.

Here's what the vulnerable dependency looked like in package-lock.json:

"node_modules/nanoid": {
  "version": "3.3.16",
  "resolved": "https://registry.npmjs.org/nanoid/-/nanoid-3.3.16.tgz",
  "integrity": "sha512-bzlKTyNJ7+LdGIIwy8ijFpIqEQIvafahV7eYykJ8Cvh42EdJeODoJ6gUJXpQJvej1BddH8OqTXZNE/KfbWAu8Q=="
}

Attack Scenario

Consider an application that allows users to configure custom alphabets for ID generation—perhaps for generating human-readable codes or specific formatting requirements. An attacker could:

1. Submit a specially crafted alphabet configuration to the application
2. Trigger the customAlphabet function with malicious parameters
3. Cause the function to enter an infinite loop
4. Exhaust server resources as the thread becomes permanently blocked
5. Repeat the attack to consume all available worker threads, causing complete denial of service

Even if user input doesn't directly reach customAlphabet, any code path that processes untrusted data and eventually calls this function could be exploited.

Real-World Impact

For the app_store application, this vulnerability could mean:
- Service unavailability: The application could become completely unresponsive
- Resource exhaustion: CPU usage spikes to 100% on affected threads
- Cascading failures: Dependent services timeout waiting for responses
- Business impact: Users unable to access the app store functionality

The Fix

The fix involves upgrading nanoid from version 3.3.16 to 3.3.17. Two files were modified to ensure the patched version is used throughout the dependency tree.

Change 1: package-lock.json Update

The direct dependency version was updated:

Before:

"node_modules/nanoid": {
  "version": "3.3.16",
  "resolved": "https://registry.npmjs.org/nanoid/-/nanoid-3.3.16.tgz",
  "integrity": "sha512-bzlKTyNJ7+LdGIIwy8ijFpIqEQIvafahV7eYykJ8Cvh42EdJeODoJ6gUJXpQJvej1BddH8OqTXZNE/KfbWAu8Q=="
}

After:

"node_modules/nanoid": {
  "version": "3.3.17",
  "resolved": "https://registry.npmjs.org/nanoid/-/nanoid-3.3.17.tgz",
  "integrity": "sha512-xQLf0A3HOMlgHq0n247/LRuAOYmB7dXJ/DvAxGvsSBij45XtBSmQycu+F8ODbHwns/XyFZagyL1+J0Offw1E0g=="
}

Change 2: package.json Override

An overrides section was added to package.json to ensure all transitive dependencies also use the patched version:

{
  "overrides": {
    "nanoid": "3.3.17"
  }
}

This override is crucial because nanoid might be pulled in by other dependencies at different versions. The override ensures that regardless of what version other packages request, npm will resolve to the secure 3.3.17 version.

Why This Works

The patched version (3.3.17) fixes the loop exit condition in the customAlphabet function, ensuring that:
- The loop always has a reachable termination point
- Malicious inputs cannot trigger infinite execution
- The function maintains its performance characteristics for valid inputs

Prevention & Best Practices

1. Keep Dependencies Updated

Regularly update your dependencies and monitor for security advisories:

# Check for known vulnerabilities
npm audit

# Update packages to their latest versions
npm update

# Use tools like npm-check-updates for major version updates
npx npm-check-updates -u

2. Use Dependency Overrides Strategically

When transitive dependencies contain vulnerabilities, use overrides to force secure versions:

{
  "overrides": {
    "vulnerable-package": "^patched.version"
  }
}

3. Implement Timeouts and Resource Limits

Protect against DoS attacks at the application level:

// Set execution timeouts for critical operations
const timeout = setTimeout(() => {
  throw new Error('Operation timed out');
}, 5000);

// Use worker threads with resource limits for untrusted operations

4. Use Security Scanning in CI/CD

Integrate security scanning into your development workflow:

# Example GitHub Actions workflow
- name: Run Trivy vulnerability scanner
  uses: aquasecurity/trivy-action@master
  with:
    scan-type: 'fs'
    scan-ref: '.'

5. Monitor OWASP Guidelines

Follow OWASP's guidance on:
- Denial of Service Prevention
- Vulnerable Dependency Management

Key Takeaways

• Transitive dependencies matter: Even if you don't directly use nanoid, it may be in your dependency tree through other packages—always check with npm ls nanoid
• The overrides field is essential: When you can't control what version a dependency requests, overrides in package.json ensures the secure version is used everywhere
• Infinite loop DoS is often overlooked: Unlike injection attacks, DoS vulnerabilities in utility functions are easy to miss but can be just as devastating
• Version 3.3.16 of nanoid is vulnerable: If your package-lock.json shows this version, you need to upgrade immediately
• Automated scanning catches what humans miss: This vulnerability was detected by Trivy scanning the package-lock.json file

How Orbis AppSec Detected This

• Source: The nanoid package version 3.3.16 in app_store/package-lock.json dependency tree
• Sink: The customAlphabet function in nanoid that contains the infinite loop vulnerability
• Missing control: No version constraint ensuring the patched nanoid version (3.3.17+) was used
• CWE: CWE-835 (Loop with Unreachable Exit Condition)
• Fix: Added version override in package.json and updated package-lock.json to use nanoid 3.3.17

Orbis AppSec automatically detected this vulnerability and opened a pull request with the fix. Try Orbis AppSec on your repositories to find and fix issues like this automatically.

Conclusion

CVE-2026-67213 demonstrates how a small utility library can introduce significant security risks into your application. The nanoid package is used by millions of projects, and this infinite loop vulnerability could have caused widespread service disruptions.

The fix was straightforward—a version upgrade from 3.3.16 to 3.3.17—but identifying the vulnerability and ensuring all transitive dependencies use the patched version requires vigilance. By implementing automated security scanning, keeping dependencies updated, and using npm overrides strategically, you can protect your applications from similar vulnerabilities.

Remember: your application is only as secure as its weakest dependency. Regular audits and automated scanning are essential components of a robust security posture.

References

• CWE-835: Loop with Unreachable Exit Condition
• OWASP Denial of Service Cheat Sheet
• OWASP Top 10 - A06:2021 Vulnerable and Outdated Components
• npm overrides documentation
• nanoid GitHub repository
• fix: upgrade nanoid to 3.3.17, 5.1.6 (CVE-2026-67213)