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