js-yaml has prototype pollution in merge (<<)
### 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/Prototype_Pollution_Prevention_Cheat_Sheet.html
describes (1)
Related CVEs.
| ID | severity | exploitable | ||
|---|---|---|---|---|
| CVE-2025-64718US | — | — | ||
js-yaml is a JavaScript YAML parser and dumper. In js-yaml before 4.1.1 and 3.14.2, it's possible for an attacker to modify the prototype of the result of a parsed yaml document vi… | ||||
references
External citations — patches, advisories, analysis.
- https://github.com/advisories/GHSA-mh29-5h37-fv8mADVISORY
- https://github.com/nodeca/js-yamlPACKAGE
- https://github.com/nodeca/js-yaml/commit/383665ff4248ec2192d1274e934462bb30426879WEB
- https://github.com/nodeca/js-yaml/commit/5278870a17454fe8621dbd8c445c412529525266WEB
- https://github.com/nodeca/js-yaml/issues/730#issuecomment-3549635876WEB
- https://github.com/nodeca/js-yaml/security/advisories/GHSA-mh29-5h37-fv8mWEB
- https://nvd.nist.gov/vuln/detail/CVE-2025-64718ADVISORY
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