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CVE-2026-46625

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

Description (CNA)

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 (CNA)

Vendor / productVersions
js-cookie / js-cookieaffected < 3.0.7

CWE

CWE-1321

References

ADP enrichment

CISA-ADP

No English description supplied.

redhat-SADP

A flaw was found in JavaScript Cookie (js-cookie). This vulnerability allows a remote attacker to manipulate cookie attributes by exploiting a prototype pollution issue within the `assign()` helper function. When processing specially crafted JSON input, the flaw enables an attacker to hijack the prototype of a cookie's attribute object. This allows the attacker to set sensitive cookie attributes such as `domain`, `secure`, `samesite`, `expires`, and `path`, potentially leading to security bypasses or session manipulation.