CVE-2026-26021

Description

### Summary A 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. ### Details The 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. ### PoC #### Steps to reproduce 1. Install latest version of set-in using npm install or cloning from git 2. Run the following code snippet: ```javascript Array.prototype.includes = () => false; const si = require('set-in'); const obj = {}; console.log({}.polluted); si(obj, [ 'constructor', 'prototype', 'polluted' ], 'yes'); console.log('{ ' + obj.polluted + ', ' + 'yes' + ' }'); // prints yes -> indicating that the patch was bypassed and prototype pollution occurred ``` #### Expected behavior Prototype pollution should be prevented and {} should not gain new properties. This should be printed on the console: ``` undefined undefined OR throw an Error ``` #### Actual behavior Object.prototype is polluted This is printed on the console: ``` undefined yes ``` ### Impact This 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. It could potentially lead to the following problems: 1. Authentication bypass 2. Denial of service 3. Remote code execution (if polluted property is passed to sinks like eval or child_process)

Affected packages (1)

• npm/set-in>= 2.0.1, < 2.0.5

CVSS scores

References (8)

• ADVISORYhttps://nvd.nist.gov/vuln/detail/CVE-2026-26021
• PATCHhttps://github.com/ahdinosaur/set-in
• WEBhttps://github.com/ahdinosaur/set-in/commit/34842cc02de3fd65d6f8bd0b268347e7b390125b
• WEBhttps://github.com/ahdinosaur/set-in/commit/6bad255961d379e4b1f5fbc52ef9dc8420816f24
• WEBhttps://github.com/ahdinosaur/set-in/commit/b8e1dabfdbd35c8d604b6324e01d03f280256c3d
• WEBhttps://github.com/ahdinosaur/set-in/commit/d87c1a09fa2edb55cd76440a67d83d1cb828df11
• WEBhttps://github.com/ahdinosaur/set-in/pull/6
• WEBhttps://github.com/ahdinosaur/set-in/security/advisories/GHSA-2c4m-g7rx-63q7