CVE-2026-67321

axios versions 0.31.1 before 0.33.0 and 1.15.1 before 1.18.0 contain an incomplete depth-limit bypass in toFormData.js when serializing objects with top-level keys ending in '{}'. Attackers who control object keys and nested values passed to axios form or parameter serialization can trigger a RangeError from JSON.stringify, causing denial of service in the affected request path.

axios versions 0.31.1 before 0.33.0 and 1.15.1 before 1.18.0 contain an incomplete depth-limit bypass in toFormData.js when serializing objects with top-level keys ending in '{}'. Attackers who control object keys and nested values passed to axios form or parameter serialization can trigger a RangeError from JSON.stringify, causing denial of service in the affected request path.

Duplicate Advisory

This advisory has been withdrawn because it is a duplicate of GHSA-hcpx-6fm6-wx23. This link is maintained to preserve external references.

Original Description

axios before 0.33.0 contains an incomplete depth-limit bypass in toFormData.js when serializing objects with top-level keys ending in '{}'. Attackers who control object keys and nested values passed to axios form or parameter serialization can trigger a RangeError from JSON.stringify, causing denial of service in the affected request path.

Summary

Axios versions in the fixed lines for GHSA-62hf-57xw-28j9 still contain an incomplete depth-limit bypass in lib/helpers/toFormData.js. When serializing an object with a top-level key ending in {}, axios calls JSON.stringify() on that value before the formSerializer.maxDepth guard can inspect the nested structure.

An attacker who can control object keys and nested values passed by an application into axios form or parameter serialization can trigger a raw RangeError: Maximum call stack size exceeded, causing a denial of service in the affected request path.

Impact

The impact is availability only. No confidentiality or integrity impact was confirmed.

Server-side applications are the primary concern when they accept user-controlled input and pass it into axios as data or params for multipart/form-data, application/x-www-form-urlencoded, or default parameter serialization. Browser impact is limited to the page or request context unless the application builds a broader failure mode around the thrown exception.

The attack requires control over a top-level object key ending in {} and a deeply nested object value. The option formSerializer.metaTokens: false is not a workaround because it only changes the emitted key name; the value is still stringified.

Affected Functionality

Affected paths include:

• lib/helpers/toFormData.js when a top-level key ends with {}.
• lib/helpers/toURLEncodedForm.js, which delegates to helpers.defaultVisitor.
• lib/helpers/AxiosURLSearchParams.js, used by default params serialization.
• Request transforms in lib/defaults/index.js when object data is serialized as multipart/form-data or application/x-www-form-urlencoded.

Unaffected paths include:

• Already-created FormData or URLSearchParams values that axios does not walk with toFormData.
• Custom paramsSerializer.serialize implementations that do not call axios toFormData.
• Non-{} deeply nested values in toFormData, which hit ERR_FORM_DATA_DEPTH_EXCEEDED as intended.

Technical Details

In lib/helpers/toFormData.js, defaultVisitor() handles top-level keys ending in {} before recursive traversal:

if (value && !path && typeof value === 'object') {
  if (utils.endsWith(key, '{}')) {
    key = metaTokens ? key : key.slice(0, -2);
    value = JSON.stringify(value);
  }
}

The depth guard is in build():

if (depth > maxDepth) {
  throw new AxiosError(
    'Object is too deeply nested (' + depth + ' levels). Max depth: ' + maxDepth,
    AxiosError.ERR_FORM_DATA_DEPTH_EXCEEDED
  );
}

For {} metatoken values, build() only sees the top-level property. The nested value is handed directly to native JSON.stringify(), which recurses internally and can throw RangeError before axios emits the intended AxiosError.

Proof of Concept of Attack

Safe local PoC with no network I/O:

import toFormData from './lib/helpers/toFormData.js';

function buildDeep(depth) {
  const head = {};
  let cur = head;

  for (let i = 0; i < depth; i += 1) {
    cur.x = {};
    cur = cur.x;
  }

  return head;
}

try {
  toFormData({ 'evil{}': buildDeep(10000) });
} catch (err) {
  console.log(err.name, err.code || '', err.message);
}

// Expected affected result:
// RangeError  Maximum call stack size exceeded

Expected fixed behavior is an AxiosError with code ERR_FORM_DATA_DEPTH_EXCEEDED.

Workarounds

Reject or depth-limit untrusted objects before passing them to axios serialization.

Strip or reject top-level keys ending in {} from untrusted objects when using axios form serialization.

For query parameters, use a custom paramsSerializer.serialize that enforces a depth limit.

For form bodies, construct FormData or URLSearchParams manually after validating input depth.

<details> <summary>Original Report</summary>

Summary

The maxDepth=100 guard added in axios 1.15.0 to fix GHSA-62hf-57xw-28j9 lives inside the build() recursion in…

axios versions 0.31.1 before 0.33.0 and 1.15.1 before 1.18.0 contain an incomplete depth-limit bypass in toFormData.js when serializing objects with top-level keys ending in '{}'. Attackers who control object keys and nested values passed to axios form or parameter serialization can trigger a RangeError from JSON.stringify, causing denial of service in the affected request path.

axios versions 0.31.1 before 0.33.0 and 1.15.1 before 1.18.0 contain an incomplete depth-limit bypass in toFormData.js when serializing objects with top-level keys ending in '{}'. Attackers who control object keys and nested values passed to axios form or parameter serialization can trigger a RangeError from JSON.stringify, causing denial of service in the affected request path.