js-yaml has prototype pollution in merge (<<)

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

5.3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

EPSS

• CVE-2025-64718: 0.42% estimated exploitation activity in the next 30 days; percentile 36.66 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Impact In js-yaml 4.1.0, 4.0.0, and 3.14.1 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. Patches Problem is patched in js-yaml 4.1.1 and 3.14.2. Workarounds You 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). References https://cheatsheetseries.owasp.org/cheatsheets/PrototypePollutionPreventionCheatSheet.html

Published by the source

14 Nov 2025, 14:29 UTC

Last modified by the source

10 Sep 2026, 03:50 UTC

Source last checked

26 Oct 2026, 12:41 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-mh29-5h37-fv8m

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-mh29-5h37-fv8m

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# Patch Next advisory brief: CVE-2025-64718

Advisory: js-yaml has prototype pollution in merge (<<)
IDs: CVE-2025-64718, GHSA-mh29-5h37-fv8m
Record: https://patchnext.com/advisories/cve-2025-64718 (revision 2, source checked 26 Oct 2026, 12:41 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: js-yaml 4.1.1, 3.14.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm js-yaml: affected >= 4.0.0, < 4.1.1; < 3.14.2; fixed in 3.14.2, 4.1.1

## Suggested inspection (read-only)
- `npm ls js-yaml --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on js-yaml.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-mh29-5h37-fv8m (OSV record GHSA-mh29-5h37-fv8m lists affected ranges: npm js-yaml >=4.0.0 =0 <3.14.2 (fixed))
- Verified: https://github.com/advisories/GHSA-mh29-5h37-fv8m (GitHub-reviewed advisory GHSA-mh29-5h37-fv8m lists affected ranges: npm js-yaml >=4.0.0 =0 <3.14.2)

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