How Denial of Service via excessive memory allocation happens in Node.js adm-zip and how to fix it

Introduction

The laliga-fantasy-app, a Node.js web service for fantasy sports, was running with a critical security flaw hiding in plain sight within its package-lock.json. The adm-zip library at version 0.5.16—used for handling ZIP file operations—contained CVE-2026-39244, a high-severity Denial of Service vulnerability that could allow remote attackers to crash the entire application with a single malicious file upload.

Since this is a web service where request handlers are directly exposed to the internet, any user-influenced ZIP file processing becomes a potential attack vector. An attacker wouldn't need authentication or special privileges—just the ability to send a crafted ZIP file to any endpoint that processes compressed archives.

The Vulnerability Explained

What Makes This Dangerous

CVE-2026-39244 exploits a fundamental flaw in how adm-zip 0.5.16 handles ZIP file parsing. When the library reads a ZIP file's central directory and local file headers, it trusts the declared uncompressed size values without proper validation. A malicious ZIP file can declare astronomically large uncompressed sizes while remaining tiny in its compressed form.

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

"dependencies": {
  "adm-zip": "^0.5.16",
  "axios": "^1.6.2",
  // ... other dependencies
}

And in package-lock.json, the resolved version:

"node_modules/adm-zip": {
  "version": "0.5.16",
  "resolved": "https://registry.npmjs.org/adm-zip/-/adm-zip-0.5.16.tgz",
  "integrity": "sha512-TGw5yVi4saajsSEgz25grObGHEUaDrniwvA2qwSC060KfqGPdglhvPMA2lPIoxs3PQIItj2iag35fONcQqgUaQ==",
  "license": "MIT",
  "engines": {
    "node": ">=12.0"
  }
}

Attack Scenario

Imagine an attacker crafting a ZIP file with the following characteristics:
- Compressed size: 1 KB
- Declared uncompressed size: 10 GB (or more)

When the laliga-fantasy-app attempts to process this file using adm-zip 0.5.16, the library allocates memory buffers based on the declared uncompressed size. This causes:

1. Immediate memory spike: Node.js attempts to allocate gigabytes of memory
2. Process crash: The V8 heap limit is exceeded, triggering an out-of-memory error
3. Service unavailability: The web service goes down, affecting all users

For a fantasy sports application, this could mean:
- Users unable to set their lineups before match deadlines
- Lost transactions during peak usage periods
- Potential cascading failures if the app is part of a larger microservices architecture

The "ZIP Bomb" Variant

This vulnerability is related to the classic "ZIP bomb" attack pattern, but specifically targets the memory allocation phase rather than disk space. Traditional ZIP bombs expand to fill disk space; this attack exhausts RAM before any data is even decompressed.

The Fix

The remediation was straightforward but critical: upgrade adm-zip to version 0.6.0, which includes proper bounds checking on memory allocation.

Before (Vulnerable)

// package.json
"dependencies": {
  "adm-zip": "^0.5.16",
  // ...
}

// package-lock.json
"node_modules/adm-zip": {
  "version": "0.5.16",
  "resolved": "https://registry.npmjs.org/adm-zip/-/adm-zip-0.5.16.tgz",
  "engines": {
    "node": ">=12.0"
  }
}

After (Fixed)

// package.json
"dependencies": {
  "adm-zip": "^0.6.0",
  // ...
}

// package-lock.json
"node_modules/adm-zip": {
  "version": "0.6.0",
  "resolved": "https://registry.npmjs.org/adm-zip/-/adm-zip-0.6.0.tgz",
  "integrity": "sha512-XleryMhbuksdKtofnWZ9Sk+4CUTbms4Mb/EU32SZwToAyZ5RgVos/ki8n+yr0LWHOGKuakbXTuuYNHLQjhddgg==",
  "engines": {
    "node": ">=14.0"
  }
}

What Changed in adm-zip 0.6.0

The new version implements several protective measures:

1. Memory allocation limits: The library now validates declared sizes against reasonable thresholds before allocating buffers
2. Decompression ratio checks: Suspicious compression ratios trigger warnings or rejections
3. Incremental processing: Large files are processed in chunks rather than loading entirely into memory
4. Node.js version requirement: The minimum Node.js version increased from 12.0 to 14.0, ensuring access to newer security APIs

The application version was also bumped from 3.4.1 to 3.5.3 to reflect this security update.

Prevention & Best Practices

1. Keep Dependencies Updated

Use automated dependency scanning in your CI/CD pipeline:

# Run Trivy to scan for vulnerable dependencies
trivy fs --scanners vuln .

# Or use npm audit
npm audit

2. Implement Defense in Depth

Even with patched libraries, add application-level protections:

// Example: Limit upload sizes at the application level
const express = require('express');
const app = express();

// Limit request body size
app.use(express.json({ limit: '10mb' }));

// For file uploads, use multer with limits
const multer = require('multer');
const upload = multer({
  limits: {
    fileSize: 50 * 1024 * 1024, // 50MB max
  }
});

3. Set Node.js Memory Limits

Configure memory limits to prevent runaway allocation from crashing your entire system:

# Limit Node.js heap to 512MB
node --max-old-space-size=512 app.js

4. Use Process Managers with Restart Policies

Deploy with PM2 or similar tools that automatically restart crashed processes:

// ecosystem.config.js
module.exports = {
  apps: [{
    name: 'laliga-fantasy-app',
    script: 'app.js',
    max_memory_restart: '500M',
    restart_delay: 1000
  }]
};

5. Monitor Memory Usage

Implement monitoring to detect memory exhaustion attempts:

// Log memory usage periodically
setInterval(() => {
  const used = process.memoryUsage();
  console.log({
    heapUsed: Math.round(used.heapUsed / 1024 / 1024) + 'MB',
    heapTotal: Math.round(used.heapTotal / 1024 / 1024) + 'MB'
  });
}, 30000);

Key Takeaways

• adm-zip 0.5.16 trusts ZIP header values without validation, allowing attackers to trigger excessive memory allocation with crafted files
• Web services processing user-uploaded ZIPs are directly exploitable without authentication when using vulnerable versions
• The laliga-fantasy-app's upgrade to adm-zip 0.6.0 adds bounds checking that prevents memory exhaustion attacks
• Dependency scanning tools like Trivy can automatically detect CVE-2026-39244 in your package-lock.json
• Defense in depth matters: even with patched libraries, implement file size limits and memory constraints at the application level

How Orbis AppSec Detected This

• Source: User-uploaded ZIP files processed by the web service
• Sink: adm-zip library's memory allocation routines when parsing ZIP headers
• Missing control: No bounds checking on declared uncompressed sizes in adm-zip 0.5.16
• CWE: CWE-400 (Uncontrolled Resource Consumption)
• Fix: Upgraded adm-zip from 0.5.16 to 0.6.0, which implements proper memory allocation limits

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-2026-39244 in adm-zip demonstrates how a single vulnerable dependency can expose an entire web service to Denial of Service attacks. The laliga-fantasy-app was at risk of complete service disruption from any user who could upload a crafted ZIP file.

The fix—upgrading from adm-zip 0.5.16 to 0.6.0—was simple to implement but critical for security. This case reinforces the importance of:

1. Automated dependency scanning in CI/CD pipelines
2. Prompt patching of known vulnerabilities
3. Defense in depth with application-level protections

Don't let your fantasy sports app (or any application) become an easy target. Keep your dependencies updated and your memory limits configured.

References

• CWE-400: Uncontrolled Resource Consumption
• OWASP Denial of Service Cheat Sheet
• npm adm-zip package
• Node.js Memory Management Documentation
• Trivy Vulnerability Scanner
• fix: upgrade adm-zip to 0.6.0 (CVE-2026-39244)