GHSA-MHWJ-73QX-JQXM
Vulnerability from github – Published: 2026-05-11 16:10 – Updated: 2026-05-11 16:10Summary
@theecryptochad/merge-guard versions prior to 1.0.1 are vulnerable to Prototype Pollution via the deepMerge() function. An attacker who controls the source object can inject __proto__ keys that mutate Object.prototype, affecting all objects in the Node.js runtime.
Details
The deepMerge() function recursively merges two objects without sanitizing reserved property keys (__proto__, constructor, prototype). When a source object contains a __proto__ key, its value is assigned to target.__proto__, which JavaScript engines interpret as a write to Object.prototype.
Proof of Concept
const { deepMerge } = require('@theecryptochad/merge-guard');
const payload = JSON.parse('{"__proto__":{"isAdmin":true}}');
deepMerge({}, payload);
console.log({}.isAdmin); // true — Object.prototype is polluted
Impact
Any application using deepMerge() with untrusted input (e.g. user-supplied JSON from HTTP requests, WebSocket messages, or config files) is vulnerable. An attacker can inject arbitrary properties onto Object.prototype, enabling privilege escalation, application logic bypass, and property injection.
Remediation
Upgrade to @theecryptochad/merge-guard >= 1.0.1, which adds an explicit blocklist:
const BLOCKED = new Set(['__proto__', 'constructor', 'prototype']);
if (BLOCKED.has(key)) continue;
References
{
"affected": [
{
"package": {
"ecosystem": "npm",
"name": "@theecryptochad/merge-guard"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "1.0.1"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [],
"database_specific": {
"cwe_ids": [
"CWE-1321"
],
"github_reviewed": true,
"github_reviewed_at": "2026-05-11T16:10:12Z",
"nvd_published_at": null,
"severity": "HIGH"
},
"details": "## Summary\n\n`@theecryptochad/merge-guard` versions prior to 1.0.1 are vulnerable to Prototype Pollution via the `deepMerge()` function. An attacker who controls the source object can inject `__proto__` keys that mutate `Object.prototype`, affecting all objects in the Node.js runtime.\n\n## Details\n\nThe `deepMerge()` function recursively merges two objects without sanitizing reserved property keys (`__proto__`, `constructor`, `prototype`). When a source object contains a `__proto__` key, its value is assigned to `target.__proto__`, which JavaScript engines interpret as a write to `Object.prototype`.\n\n## Proof of Concept\n\n```js\nconst { deepMerge } = require(\u0027@theecryptochad/merge-guard\u0027);\nconst payload = JSON.parse(\u0027{\"__proto__\":{\"isAdmin\":true}}\u0027);\ndeepMerge({}, payload);\nconsole.log({}.isAdmin); // true \u2014 Object.prototype is polluted\n```\n\n## Impact\n\nAny application using `deepMerge()` with untrusted input (e.g. user-supplied JSON from HTTP requests, WebSocket messages, or config files) is vulnerable. An attacker can inject arbitrary properties onto `Object.prototype`, enabling privilege escalation, application logic bypass, and property injection.\n\n## Remediation\n\nUpgrade to `@theecryptochad/merge-guard \u003e= 1.0.1`, which adds an explicit blocklist:\n\n```js\nconst BLOCKED = new Set([\u0027__proto__\u0027, \u0027constructor\u0027, \u0027prototype\u0027]);\nif (BLOCKED.has(key)) continue;\n```\n\n## References\n- [CWE-1321: Improper Neutralization of Special Elements in Object Keys](https://cwe.mitre.org/data/definitions/1321.html)\n- [OWASP: Prototype Pollution](https://owasp.org/www-community/attacks/Prototype_Pollution)\n- [Fix commit](https://github.com/TheeCryptoChad/merge-guard/releases/tag/v1.0.1)",
"id": "GHSA-mhwj-73qx-jqxm",
"modified": "2026-05-11T16:10:12Z",
"published": "2026-05-11T16:10:12Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/TheeCryptoChad/merge-guard/security/advisories/GHSA-mhwj-73qx-jqxm"
},
{
"type": "WEB",
"url": "https://github.com/TheeCryptoChad/merge-guard/commit/25e4b4f2618578a656ef3cb4946a1b475f736736"
},
{
"type": "PACKAGE",
"url": "https://github.com/TheeCryptoChad/merge-guard"
}
],
"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:N",
"type": "CVSS_V3"
}
],
"summary": "@theecryptochad/merge-guard has Prototype Pollution in its deepMerge() function"
}
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