nodejs/node

FATAL ERROR: v8::ToLocalChecked Empty MaybeLocal

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#56531 opened on Jan 9, 2025

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 (11 comments) (0 reactions) (0 assignees)JavaScript (117,218 stars) (35,535 forks)batch import
c++child_processgood first issue

Description

Version

v23.6.0

Platform

Linux SMP Debian 5.10.103-1 (2022-03-07) x86_64 x86_64 x86_64 GNU/Linux

Subsystem

No response

What steps will reproduce the bug?

Hi,

I would like to report a bug, it can be reproduced by running the PoC below:

const {exec} = require('child_process');

Object.defineProperty(Array.prototype, "2", {
  set: function () {},
});

(async function () {
  exec('pwd', (err, stdout, stderr) => {
    console.log(stdout);
  });
})();

Regards,

AH

How often does it reproduce? Is there a required condition?

It reproduces anytime by simply running the given PoC on the given Node.js version.

What is the expected behavior? Why is that the expected behavior?

It is a crash.

What do you see instead?

FATAL ERROR: v8::ToLocalChecked Empty MaybeLocal

Additional information

No response

Contributor guide

Tech stack
nodejsjavascript
Domain
backend
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
JavaScriptNode.js
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40
Research direction
The crash occurs when Array.prototype has a custom setter, causing v8 to fail when getting array indices during child process execution. The PoC uses `exec` from `child process` module. Look at the child process source code in Node.js (lib/child process.js) to understand how array operations are performed. The FATAL ERROR indicates v8's ToLocalChecked is called on an empty MaybeLocal, which is an internal v8 error. Consult comments for potential solutions, like using a different method to access array elements that avoids triggering setters. No linked PRs or assignees, so this is open for new contributors.