GHSA-MHWJ-73QX-JQXM

@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

References

• CWE-1321: Improper Neutralization of Special Elements in Object Keys
• OWASP: Prototype Pollution
• Fix commit

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.

GHSA-MHWJ-73QX-JQXM has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.0.1); upgrading removes the vulnerable code path.

Kodem intelligence

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;

1. What is GHSA-MHWJ-73QX-JQXM? GHSA-MHWJ-73QX-JQXM is a high-severity security vulnerability in @theecryptochad/merge-guard (npm), affecting versions < 1.0.1. It is fixed in 1.0.1.
2. How severe is GHSA-MHWJ-73QX-JQXM? GHSA-MHWJ-73QX-JQXM has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of @theecryptochad/merge-guard are affected by GHSA-MHWJ-73QX-JQXM? @theecryptochad/merge-guard (npm) versions < 1.0.1 is affected.
4. Is there a fix for GHSA-MHWJ-73QX-JQXM? Yes. GHSA-MHWJ-73QX-JQXM is fixed in 1.0.1. Upgrade to this version or later.
5. Is GHSA-MHWJ-73QX-JQXM exploitable, and should I be worried? Whether GHSA-MHWJ-73QX-JQXM is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether GHSA-MHWJ-73QX-JQXM is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix GHSA-MHWJ-73QX-JQXM? Upgrade @theecryptochad/merge-guard to 1.0.1 or later.