CVE-2026-46625

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.

Weakness classification

• security-advisories@github.com: CWE-1321
• 0b0ca135-0b70-47e7-9f44-1890c2a1c46c: CWE-915

Primary references

• security-advisories@github.com — Patch
• security-advisories@github.com — Release Notes
• security-advisories@github.com — Exploit, Vendor Advisory
• 0b0ca135-0b70-47e7-9f44-1890c2a1c46c — Third Party Advisory
• 0b0ca135-0b70-47e7-9f44-1890c2a1c46c — Third Party Advisory
• 0b0ca135-0b70-47e7-9f44-1890c2a1c46c — Third Party Advisory
• 0b0ca135-0b70-47e7-9f44-1890c2a1c46c — Third Party Advisory
• 0b0ca135-0b70-47e7-9f44-1890c2a1c46c — Third Party Advisory
• 0b0ca135-0b70-47e7-9f44-1890c2a1c46c — Third Party Advisory
• 0b0ca135-0b70-47e7-9f44-1890c2a1c46c — Third Party Advisory
• 0b0ca135-0b70-47e7-9f44-1890c2a1c46c — Third Party Advisory
• 0b0ca135-0b70-47e7-9f44-1890c2a1c46c — Third Party Advisory