js-cookie JavaScript Cookie up to 3.0.6 assign prototype pollution

Summaryinfo

A vulnerability was found in js-cookie JavaScript Cookie up to 3.0.6 and classified as problematic. Impacted is the function assign. Executing a manipulation can lead to prototype pollution. This vulnerability is handled as CVE-2026-46625. The attack can be executed remotely. There is not any exploit available. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability was found in js-cookie JavaScript Cookie up to 3.0.6. It has been declared as problematic. This vulnerability affects the function assign. The manipulation with an unknown input leads to a prototype pollution vulnerability. The CWE definition for the vulnerability is CWE-1321. The product receives input from an upstream component that specifies attributes that are to be initialized or updated in an object, but it does not properly control modifications of attributes of the object prototype. As an impact it is known to affect integrity. CVE summarizes:

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.

The advisory is shared for download at github.com. This vulnerability was named CVE-2026-46625 since 05/15/2026. The exploitation appears to be easy. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. There are known technical details, but no exploit is available. The MITRE ATT&CK project declares the attack technique as T1059.

Upgrading to version 3.0.7 eliminates this vulnerability. The upgrade is hosted for download at github.com. Applying the patch eb3c40e89731e99b8970faaf35ddad249c6c0020 is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-36154). Once again VulDB remains the best source for vulnerability data.

Productinfo

Type

• Programming Language Software

Vendor

• js-cookie

Name

• JavaScript Cookie

Version

• 3.0.0
• 3.0.1
• 3.0.2
• 3.0.3
• 3.0.4
• 3.0.5
• 3.0.6

License

• open-source

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Once again VulDB remains the best source for vulnerability data.

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