---
id: GHSA-jggr-w7fw-pc2j
title: 'fast-copy: Stack exhaustion in fast-copy when copying deeply-nested values'
summary: 'fast-copy: Stack exhaustion in fast-copy when copying deeply-nested values'
severity: medium
cwe:
  - CWE-674
vendor: fast-copy
product: fast-copy
ecosystem: npm
affected:
  - 'fast-copy >= 4.0.0, < 4.1.0'
  - 'fast-copy >= 3.0.0, < 3.1.0'
  - fast-copy < 2.2.0
patched:
  - fast-copy 4.1.0
  - fast-copy 3.1.0
  - fast-copy 2.2.0
published: '2026-10-05'
updated: '2026-10-05'
sourceUpdated: '2026-10-05T22:52:12Z'
source: GHSA
sourceUrl: 'https://github.com/advisories/GHSA-jggr-w7fw-pc2j'
references:
  - url: >-
      https://github.com/planttheidea/fast-copy/security/advisories/GHSA-jggr-w7fw-pc2j
  - url: 'https://github.com/planttheidea/fast-copy/pull/137'
  - url: 'https://github.com/planttheidea/fast-copy/pull/138'
  - url: 'https://github.com/planttheidea/fast-copy/pull/139'
  - url: >-
      https://github.com/planttheidea/fast-copy/commit/359c00884ae8ae31f10925fd0e2fc66661db6cef
  - url: >-
      https://github.com/planttheidea/fast-copy/commit/caa7caace65767dfe252f0dc5115d82c99ca16b9
  - url: >-
      https://github.com/planttheidea/fast-copy/commit/dedf465e5329fbd149f13b53521af962d16ff8df
  - url: 'https://github.com/planttheidea/fast-copy/releases/tag/v2.2.0'
  - url: 'https://github.com/planttheidea/fast-copy/releases/tag/v3.1.0'
  - url: 'https://github.com/planttheidea/fast-copy/releases/tag/v4.1.0'
  - url: 'https://github.com/advisories/GHSA-jggr-w7fw-pc2j'
tags:
  - ghsa
  - npm
ingestedAt: '2026-10-05T23:36:21.174Z'
---

## Overview

## Summary

`fast-copy` traverses values recursively with no bound on depth. Copying a sufficiently deeply-nested value exhausts the JavaScript call stack and throws a native `RangeError: Maximum call stack size exceeded` from inside the library.

## Details

Both `copy` and `copyStrict` recurse once per level of nesting. The value does not need to be circular (circular references were already handled correctly via an internal cache) and it does not need to be large. A plain object nested a few thousand levels deep is only a few
kilobytes of equivalent JSON.

Measured depths at which copying begins to fail (Node.js, V8; the exact ceiling varies with JIT state and the stack available to the environment):

| Call                 | Last depth that copies successfully |
| -------------------- | ----------------------------------- |
| `copy(object)`       | 2811                                |
| `copy(array)`        | 3983                                |
| `copyStrict(object)` | 1874                                |
| `copyStrict(array)`  | 1874                                |

`JSON.parse` is iterative and parses deeply-nested input without difficulty, so a payload that deserializes cleanly can fail in a subsequent `copy` call.

## Impact

The failure is a synchronous, catchable `RangeError` confined to the `copy` call that received the value. There are no memory safety concerns, no data exposure, and no effect on state outside that call. In a typical server the result is a failed request rather than a failed process.

Applications that call `copy` on externally-supplied data, such as request bodies, cached payloads, merged configuration, etc., do not expect a clone helper to throw may surface this as an unhandled error.

## Patches

Fixed in 4.1.0, and backported to 3.1.0 and 2.2.0 so that every major line has a patch available without requiring a breaking upgrade.

Traversal is now bounded by a `maxDepth` option, defaulting to `1000`, which sits below the native limit in standard environments. Exceeding it throws `MaxDepthExceededError`, which carries the limit that was exceeded and extends `RangeError` so existing handling continues to match.

The limit is configurable for consumers with legitimately deep data. On `3.x` and `4.x` it is set when creating a copier:

```js
import { createCopier } from 'fast-copy';

export const copy = createCopier({ maxDepth: 5000 });
```

On `2.x` it is passed per call, and the error is a property of the exported function rather than a named export:

```js
import copy from 'fast-copy';

copy(value, { maxDepth: 5000 });
// detection: error instanceof copy.MaxDepthExceededError
```

In legacy environments without `Object.setPrototypeOf`, `instanceof MaxDepthExceededError` cannot be supported; check `error.name === 'MaxDepthExceededError'` or `error instanceof RangeError` instead.

## Affected packages

- `fast-copy >= 4.0.0, < 4.1.0`
- `fast-copy >= 3.0.0, < 3.1.0`
- `fast-copy < 2.2.0`

## Remediation

Upgrade to a patched release:

- `fast-copy 4.1.0`
- `fast-copy 3.1.0`
- `fast-copy 2.2.0`