CVE-2025-64718: js-yaml prototype pollution in merge operator

CVE-2025-64718 · Severity: medium · CVSS 5.3 · Published 2025-11-13

js-yaml is a popular YAML parser used in Node.js applications. The library contains a prototype pollution vulnerability in its merge operation (<<) that allows attackers to modify object prototypes when parsing untrusted YAML documents. This could enable attackers to inject malicious properties into application objects, leading to unexpected behavior, authentication bypass, or code execution depending on how the application uses the parsed data.

Technologies: js-yaml (npm). Vendors: npm.

Quick answers

Is CVE-2025-64718 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2025-64718 being exploited in the wild.
How severe is CVE-2025-64718?
Medium severity, with a CVSS score of 5.3, published 13 November 2025.
Which products and versions are affected?
js-yaml (npm) SEMVER:introduced=4.0.0,fixed=4.1.1.
Is there a fix for CVE-2025-64718?
Yes. js-yaml (npm): upgrade to 4.1.1 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2025-64718 attacked?
It is attacked over the network.
Am I affected by CVE-2025-64718?
Check whether you run js-yaml (npm) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • js-yaml (npm): upgrade to 4.1.1 or later
    npm install js-yaml@4.1.1

Technical details

The vulnerability is a prototype pollution flaw in js-yaml versions 4.0.0–4.1.0 and below 3.14.2, occurring in the merge operator (<<) during YAML deserialization. An attacker can craft a malicious YAML document that pollutes the Object prototype by setting __proto__ properties, affecting all objects created after parsing. The attack requires the application to parse untrusted YAML input and does not require authentication or network access beyond submitting the YAML payload. The impact ranges from object property manipulation to potential code execution if the application relies on prototype-based logic. Patches are available in js-yaml 4.1.1 and 3.14.2.

Affected products

  • nodeca js-yaml >=4.0.0, <4.1.1 and <3.14.2

Identifiers

  • CVE-2025-64718
  • GHSA-mh29-5h37-fv8m

Timeline

  • 2025-11-12: disclosed
  • 2025-11-12: patched: Patched in js-yaml 4.1.1 and 3.14.2

References

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