CVE-2026-46625: JavaScript Cookie: Per-instance prototype hijack in assign() enables cookie-attribute injection

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.9% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-06-10 · updated 2026-09-09
Weakness: CWE-1321

Description

JavaScript Cookie is a JavaScript API for handling cookies, client-side. Prior to version 3.0.7, 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 ({}). The result is a per-instance prototype hijack: Object.prototype itself is untouched, but the merged attributes object now inherits attacker-controlled keys. Because the consuming set() function then enumerates the merged object with another for...in, every key the attacker placed on the polluted prototype lands in the resulting Set-Cookie string as an attribute pair. The attacker can set domain=, secure=, samesite=, expires=, and path= on cookies whose attributes the developer thought were locked down. This issue has been patched in version 3.0.7.

Affected products

js-cookie Javascript Cookie: before 3.0.7 — fixed in 3.0.7
Red Hat 3scale API Management Platform 2: 2.0
Red Hat Ansible Automation Platform: 2.0
Red Hat Enterprise Linux: 8.0, 9.0, 10.0
Red Hat OpenShift AI 2.25: all versions
Red Hat OpenShift Lightspeed: all versions

How to fix

Upgrade to a fixed version: js-cookie Javascript Cookie 3.0.7. Check the vendor advisory for mitigations.

References

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