JavaScript Cookie: Per-instance prototype hijack in assign() enables cookie-attribute injection

Description

js-cookie’s internal assign() helper copies properties with for...in + plain assignment. When the source object is produced by JSON.parse, the JSON object’s "__proto__" member is an own enumerable property, so the for…in enumerates it and the target[key] = source[key] write triggers the Object.prototype.__proto__ setter on the fresh target ({}).

Recommendation

Update the js-cookie package to the latest compatible version. Followings are version details:

• Affected version(s): <= 3.0.5
• Patched version(s): 3.0.7

References

• GHSA-qjx8-664m-686j
• CVE-2026-46625
• CWE-1321
• CAPEC-310
• OWASP 2021-A6

Related Issues

• Axios has prototype pollution read-side gadgets in HTTP adapter that allow credential injection and request hijacking - CVE-2026-42264
• jsPDF has a PDF Injection in AcroForm module allows Arbitrary JavaScript Execution (RadioButton.createOption and "AS" pr - CVE-2026-25940
• Svelte SSR attribute spreading includes inherited properties from prototype chain - CVE-2026-27125
• protobuf.js: Prototype injection in generated message constructors - CVE-2026-44292

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Tags:

npm

js-cookie