When Your Next.js App Just… Dies: The Sneaky Stack Overflow Bug That’s Been Crashing Servers

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Hey fellow devs! 👋

So, picture this: You’re working on your Next.js app, everything’s running smooth, your tests are passing, code review looks good. You deploy to production and… boom. Your server just dies. No error logs. No catchable exceptions. Just exit code 7 and your app is gone.

Sound familiar? Well, you’re not alone. This exact scenario has been haunting full-stack developers for months, and it all comes down to a sneaky bug in Node.js that just got fixed in January 2026. Let’s dig into what went wrong and how to protect your apps.

What Even Happened?

Here’s the deal: There was a critical vulnerability in Node.js (CVE-2025-59466) that could crash your entire application when deep recursion met a little thing called async_hooks. And the worst part? Your error handlers couldn’t catch it.

This wasn’t just some theoretical bug either. It was actively affecting:

  • React Server Components
  • Next.js applications
  • Every major APM tool (Datadog, New Relic, Dynatrace, Elastic APM, OpenTelemetry)
  • Literally any app using AsyncLocalStorage

Yeah, that’s basically everyone building modern full-stack apps.

The Real-World Problem

Let me paint you a picture. You’re building a typical full-stack app with Next.js. Maybe you’re processing some user-submitted JSON, parsing nested objects, or traversing a deep data structure. Normal stuff, right? 

// Looks innocent enough, right?
async function processNestedData(data, depth = 0) {
  if (depth > 100) return; // You even added a safety check!

  if (typeof data === 'object') {
    for (let key in data) {
      await processNestedData(data[key], depth + 1);
    }
  }

  return data;
}

Now imagine a malicious user (or even just bad data) sends you something like this: 

// Deeply nested object that looks like: {a: {a: {a: {a: ... }}}}
let evil = {};
let current = evil;
for (let i = 0; i < 10000; i++) {
  current.a = {};
  current = current.a;
}

When your code tries to process this, it goes deep. Really deep. And here’s where things get weird.

The Technical Breakdown (Don’t Worry, I’ll Keep It Simple)

Node.js has this thing called async_hooks that tracks asynchronous operations. It’s super useful and powers a lot of the magic in modern frameworks. AsyncLocalStorage (which Next.js and React Server Components rely on) uses it under the hood.

The problem? When your code hits maximum recursion depth while async_hooks is active, instead of throwing a nice catchable error, Node.js just… exits. Straight up quits with code 7. 

// What SHOULD happen
try {
  deeplyNestedFunction(); // Causes stack overflow
} catch (error) {
  console.log('Caught it!', error); // This works normally
  // Handle gracefully, log, restart, whatever
}

// What ACTUALLY happened with the bug
try {
  deeplyNestedFunction(); // Causes stack overflow
} catch (error) {
  // This never runs when async_hooks is active
}
// Process just exits with code 7 - no warning, no logs, nothing

Your process.on('uncaughtException') handlers? Useless. Your try-catch blocks? Ignored. Your monitoring? Shows your server just disappeared.

The Discovery Story

This is actually a pretty cool piece of recent history. In early December 2025, the React and Next.js teams at Meta and Vercel started getting reports of mysterious server crashes. Users would hit certain endpoints, and bam – server down.

Here’s the timeline:

  • Dec 7, 2025: React/Next.js team reaches out to Node.js maintainers
  • Dec 8: Official security report filed
  • Dec 9-11: Multiple patch attempts (first ones didn’t work!)
  • Dec 12: They find a blocker in the patch strategy
  • Dec 16: Node.js decides this needs special handling
  • Dec 17: Fix is finalized
  • Jan 13, 2026: Patched versions released

So if you’re running Node.js and haven’t updated since mid-January 2026, you’re vulnerable.

How to Reproduce This Bug (For Science!)

Want to see it in action? Here’s a minimal reproduction: 

const { AsyncLocalStorage } = require('async_hooks');
const als = new AsyncLocalStorage();

// This function will cause deep recursion
function causeChaos(n) {
  if (n <= 0) return;
  causeChaos(n - 1); // Recursive call with no base case hit
}

// Wrap it in AsyncLocalStorage context
als.run(new Map(), () => {
  try {
    causeChaos(100000); // This will overflow the stack
    console.log('This never prints');
  } catch (error) {
    console.log('Neither does this'); // Bug: catch block never executes
  }
});

console.log('Server kept running!'); // This also never prints
// Instead, process exits with code 7

Before the patch: Process crashes immediately, no error caught.

After the patch: Error is properly caught and handled.

The Fix (And How to Protect Yourself)

The Node.js team released patches for versions 20.x, 22.x, 24.x, and 25.x. But here’s the thing – even with the patch, you shouldn’t rely on stack overflow error handling for security or availability.

Here’s what you should actually do:

1. Update Node.js IMMEDIATELY

# Check your version
node --version

# Update to patched versions:
# v20.x → v20.18.2 or later
# v22.x → v22.13.2 or later  
# v24.x → v24.0.2 or later
# v25.x → v25.3.0 or later

2. Validate Input Depth

Don’t let users control how deep your recursion goes. Add real checks: 

function safeProcessData(data, maxDepth = 50) {
  function process(obj, currentDepth = 0) {
    if (currentDepth > maxDepth) {
      throw new Error(`Data nesting exceeds maximum depth of ${maxDepth}`);
    }

    if (typeof obj !== 'object' || obj === null) {
      return obj;
    }

    const result = Array.isArray(obj) ? [] : {};
    for (let key in obj) {
      result[key] = process(obj[key], currentDepth + 1);
    }

    return result;
  }

  return process(data);
}

// Use it like this
app.post('/api/data', (req, res) => {
  try {
    const safeData = safeProcessData(req.body, 50);
    // Process safeData...
    res.json({ success: true });
  } catch (error) {
    res.status(400).json({ error: error.message });
  }
});

3. Use Iteration Instead of Recursion

When possible, flatten your approach: 

// Instead of recursive traversal
function recursiveSum(arr) {
  if (!Array.isArray(arr)) return arr;
  return arr.reduce((sum, item) => sum + recursiveSum(item), 0);
}

// Use iterative approach
function iterativeSum(arr) {
  const stack = [...arr];
  let sum = 0;

  while (stack.length > 0) {
    const item = stack.pop();
    if (Array.isArray(item)) {
      stack.push(...item);
    } else {
      sum += item;
    }
  }

  return sum;
}

4. Add Request Size Limits

Don’t even let huge payloads reach your code: 

const express = require('express');
const app = express();

// Limit JSON payload size
app.use(express.json({ 
  limit: '100kb',
  verify: (req, res, buf, encoding) => {
    // Additional validation if needed
    if (buf.length > 100000) {
      throw new Error('Request too large');
    }
  }
}));

5. Monitor Your Deployment

Set up proper monitoring so you catch crashes: 

// Add process exit handlers
process.on('exit', (code) => {
  console.error(`Process exiting with code: ${code}`);
  // Log to your monitoring service
});

process.on('uncaughtException', (error) => {
  console.error('Uncaught Exception:', error);
  // Send to error tracking (Sentry, etc.)
  process.exit(1);
});

Testing Your Fix

Here’s a simple test to verify your app is protected: 

// test/stack-overflow.test.js
const request = require('supertest');
const app = require('../app');

describe('Stack Overflow Protection', () => {
  it('should reject deeply nested JSON', async () => {
    // Create evil deeply nested object
    let evil = { data: 'value' };
    let current = evil;

    for (let i = 0; i < 200; i++) {
      current.nested = { layer: i };
      current = current.nested;
    }

    const response = await request(app)
      .post('/api/process')
      .send(evil)
      .expect(400);

    expect(response.body.error).toMatch(/depth|nesting/i);
  });

  it('should handle normal nested data fine', async () => {
    const normalData = {
      user: {
        profile: {
          settings: {
            theme: 'dark'
          }
        }
      }
    };

    const response = await request(app)
      .post('/api/process')
      .send(normalData)
      .expect(200);

    expect(response.body.success).toBe(true);
  });
});

The Bigger Picture

This bug is a perfect example of why full-stack development in 2026 is wild. You’ve got:

  • Frontend frameworks (React, Next.js) doing server-side magic
  • Backend systems relying on low-level Node.js APIs
  • Cloud providers running your code in mysterious ways
  • APM tools trying to track it all

And when one tiny piece breaks, the whole stack can come crashing down.

The key lesson? Don’t trust the runtime to save you. Even after this fix, the Node.js team says you shouldn’t rely on stack overflow handling for availability. Build defensive code from the start.

Quick Checklist for Full-Stack Devs

Before you ship your next feature:

  • [ ] Updated to latest Node.js patch version
  • [ ] Input validation with depth limits on all user data
  • [ ] Request size limits configured
  • [ ] Recursion replaced with iteration where possible
  • [ ] Error monitoring set up (Sentry, Datadog, etc.)
  • [ ] Exit code 7 alerts configured
  • [ ] Integration tests covering edge cases
  • [ ] Load testing with malicious payloads

What This Means for Your Stack

If you’re running:

Next.js: Update Node.js immediately. The framework relies heavily on async_hooks for Server Components.

Express/Fastify: Still vulnerable if you use AsyncLocalStorage for request context. Update and add input validation.

NestJS: Same deal – update Node.js and audit your recursive logic.

Serverless (Lambda, Vercel, etc.): Check your runtime version. Most providers auto-update, but verify.

Final Thoughts

Look, bugs happen. Even in battle-tested tech like Node.js. The important thing is staying informed and protecting your apps proactively.

This vulnerability taught us that the “happy path” isn’t enough. You need to think about what happens when users send you weird data, when systems behave unexpectedly, when the stack overflows.

Write defensive code. Validate inputs. Test edge cases. Monitor everything.

And for the love of all things JavaScript, keep your Node.js updated!

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