BaseFortify

Publication date: 2025-11-13

Last updated on: 2025-12-02

Assigner: GitHub, Inc.

Description

js-yaml is a JavaScript YAML parser and dumper. In js-yaml 4.1.0 and below, it's possible for an attacker to modify the prototype of the result of a parsed yaml document via prototype pollution (`__proto__`). All users who parse untrusted yaml documents may be impacted. The problem is patched in js-yaml 4.1.1. Users can protect against this kind of attack on the server by using `node --disable-proto=delete` or `deno` (in Deno, pollution protection is on by default).

CVSS Scores

EPSS Scores

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Meta Information

Published

2025-11-13

Last Modified

2025-12-02

Generated

2026-07-06

AI Q&A

2025-11-13

EPSS Evaluated

2026-07-05

NVD

CVE-2025-64718

Affected Vendors & Products

Vendor	Product	Version / Range
nodeca	js-yaml	to 4.1.1 (exc)

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
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.

Attack-Flow Graph

Executive Summary

This vulnerability in js-yaml versions 4.1.0 and below allows an attacker to modify the prototype of the object resulting from parsing a YAML document through prototype pollution using the __proto__ property. This means that if an attacker provides a malicious YAML document, they can manipulate the internal structure of the parsed object, potentially leading to unexpected behavior or security issues.

Impact Analysis

If you parse untrusted YAML documents using vulnerable versions of js-yaml, an attacker could exploit this vulnerability to perform prototype pollution, which may lead to altered application behavior or security risks. This could affect the integrity of your application and potentially allow further attacks depending on how the parsed data is used.

Mitigation Strategies

To mitigate this vulnerability, update js-yaml to version 4.1.1 or later. Additionally, on the server side, you can protect against prototype pollution by running Node.js with the flag `--disable-proto=delete`. Using Deno is also a mitigation option since it has pollution protection enabled by default.

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