GHSA-62HF-57XW-28J9

Vulnerability from github – Published: 2026-05-05 00:34 – Updated: 2026-06-08 15:54
VLAI
Summary
Axios: unbounded recursion in toFormData causes DoS via deeply nested request data
Details

Summary

toFormData recursively walks nested objects with no depth limit, so a deeply nested value passed as request data crashes the Node.js process with a RangeError.

Details

lib/helpers/toFormData.js:210 defines an inner build(value, path) that recurses into every object/array child (line 225: build(el, path ? path.concat(key) : [key])). The only safeguard is a stack array used to detect circular references; there is no maximum depth and no try/catch around the recursion. Because build calls itself once per nesting level, a payload nested roughly 2000+ levels deep exhausts V8's call stack.

toFormData is the serializer behind FormData request bodies and AxiosURLSearchParams (used by buildURL when params is an object with URLSearchParams unavailable, see lib/helpers/buildURL.js:53 and lib/helpers/AxiosURLSearchParams.js:36). Any server-side code that forwards a client-supplied object into axios({ data, params }) therefore reaches the recursive walker with attacker-controlled depth.

The RangeError is thrown synchronously from inside forEach, escapes toFormData, and propagates out of the axios request call. In typical Express/Fastify request handlers this terminates the running request; in synchronous startup paths or worker threads it can crash the whole process.

PoC

import toFormData from 'axios/lib/helpers/toFormData.js';
import FormData from 'form-data';

function nest(depth) {
  let o = { leaf: 1 };
  for (let i = 0; i < depth; i++) o = { a: o };
  return o;
}

try {
  toFormData(nest(2500), new FormData());
} catch (e) {
  console.log(e.name + ': ' + e.message);
}
// RangeError: Maximum call stack size exceeded

Server-side reachability example:

// vulnerable proxy pattern
app.post('/forward', async (req, res) => {
  await axios.post('https://upstream/api', req.body); // req.body user-controlled
  res.send('ok');
});
// attacker POST /forward with {"a":{"a":{"a":... 2500 deep ...}}}
// -> toFormData build() overflows -> request handler crashes

Verified on axios 1.15.0 (latest, 2026-04-10), Node.js 20, 3/3 PoC runs reproduce the RangeError at depth 2500.

Impact

A remote, unauthenticated attacker who can influence an object passed to axios as request data or params triggers an uncaught RangeError inside the synchronous recursive walker. In server-side applications that proxy or re-send client JSON through axios this crashes the request handler and, in worker/cluster setups, the process. Fix by bounding recursion depth in toFormData's build function (reject or throw on depths beyond a configurable limit, e.g. 100) or rewriting the walker iteratively.

Severity
7.5 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
6.9 (Medium)
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N
Show details on source website
To clipboard 

{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "axios"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "1.0.0"
            },
            {
              "fixed": "1.15.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 0.31.0"
      },
      "package": {
        "ecosystem": "npm",
        "name": "axios"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0.31.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-42039"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-674"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-05-05T00:34:32Z",
    "nvd_published_at": "2026-04-24T18:16:30Z",
    "severity": "MODERATE"
  },
  "details": "### Summary\ntoFormData recursively walks nested objects with no depth limit, so a deeply nested value passed as request data crashes the Node.js process with a RangeError.\n\n### Details\nlib/helpers/toFormData.js:210 defines an inner `build(value, path)` that recurses into every object/array child (line 225: `build(el, path ? path.concat(key) : [key])`). The only safeguard is a `stack` array used to detect circular references; there is no maximum depth and no try/catch around the recursion. Because `build` calls itself once per nesting level, a payload nested roughly 2000+ levels deep exhausts V8\u0027s call stack.\n\n`toFormData` is the serializer behind `FormData` request bodies and `AxiosURLSearchParams` (used by `buildURL` when `params` is an object with `URLSearchParams` unavailable, see `lib/helpers/buildURL.js:53` and `lib/helpers/AxiosURLSearchParams.js:36`). Any server-side code that forwards a client-supplied object into `axios({ data, params })` therefore reaches the recursive walker with attacker-controlled depth.\n\nThe RangeError is thrown synchronously from inside `forEach`, escapes `toFormData`, and propagates out of the axios request call. In typical Express/Fastify request handlers this terminates the running request; in synchronous startup paths or worker threads it can crash the whole process.\n\n### PoC\n```js\nimport toFormData from \u0027axios/lib/helpers/toFormData.js\u0027;\nimport FormData from \u0027form-data\u0027;\n\nfunction nest(depth) {\n  let o = { leaf: 1 };\n  for (let i = 0; i \u003c depth; i++) o = { a: o };\n  return o;\n}\n\ntry {\n  toFormData(nest(2500), new FormData());\n} catch (e) {\n  console.log(e.name + \u0027: \u0027 + e.message);\n}\n// RangeError: Maximum call stack size exceeded\n```\n\nServer-side reachability example:\n```js\n// vulnerable proxy pattern\napp.post(\u0027/forward\u0027, async (req, res) =\u003e {\n  await axios.post(\u0027https://upstream/api\u0027, req.body); // req.body user-controlled\n  res.send(\u0027ok\u0027);\n});\n// attacker POST /forward with {\"a\":{\"a\":{\"a\":... 2500 deep ...}}}\n// -\u003e toFormData build() overflows -\u003e request handler crashes\n```\n\nVerified on axios 1.15.0 (latest, 2026-04-10), Node.js 20, 3/3 PoC runs reproduce the RangeError at depth 2500.\n\n### Impact\nA remote, unauthenticated attacker who can influence an object passed to axios as request `data` or `params` triggers an uncaught RangeError inside the synchronous recursive walker. In server-side applications that proxy or re-send client JSON through axios this crashes the request handler and, in worker/cluster setups, the process. Fix by bounding recursion depth in `toFormData`\u0027s `build` function (reject or throw on depths beyond a configurable limit, e.g. 100) or rewriting the walker iteratively.",
  "id": "GHSA-62hf-57xw-28j9",
  "modified": "2026-06-08T15:54:28Z",
  "published": "2026-05-05T00:34:32Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/axios/axios/security/advisories/GHSA-62hf-57xw-28j9"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-42039"
    },
    {
      "type": "WEB",
      "url": "https://github.com/axios/axios/commit/85132ffba1a77609ea5d101c8a413dea7174932f"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/axios/axios"
    },
    {
      "type": "WEB",
      "url": "https://github.com/axios/axios/releases/tag/v1.15.1"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    },
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Axios: unbounded recursion in toFormData causes DoS via deeply nested request data"
}



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