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

7.5 / 10

HIGH

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

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.

Basic Information

ID CVE-2026-46625

Source GitHub_M

Published Jun 10, 2026 at 21:18

Affected Product

Vendor js-cookie

Product js-cookie

Version < 3.0.7

Affected Versions js-cookie js-cookie < 3.0.7

CWE Classification

CWE-1321

References

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    "published": "2026-06-10T21:18:05.372Z",
    "modified": "2026-06-10T21:18:05.372Z",
    "type": "cve",
    "title": "JavaScript Cookie: Per-instance prototype hijack in assign() enables cookie-attribute injection",
    "source": "GitHub_M",
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JavaScript Cookie: Per-instance prototype hijack in assign() enables cookie-attribute injection_CVE-2026-46625