CVE-2026-46625

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.

• CWE-1321

• https://github.com/js-cookie/js-cookie/commit/eb3c40e89731e99b8970faaf35ddad249c6c0020
• https://github.com/js-cookie/js-cookie/releases/tag/v3.0.7
• https://github.com/js-cookie/js-cookie/security/advisories/GHSA-qjx8-664m-686j
• https://github.com/js-cookie/js-cookie/security/advisories/GHSA-qjx8-664m-686j

Published

Jun 10, 2026

Last Modified

Jun 17, 2026

Status

Awaiting Analysis