GHSA-mh29-5h37-fv8m CVE-2025-64718
js-yaml has prototype pollution in merge (<<)
- Severity
- 5.3 / 10
- Medium · CVSS 3.1
- Exploit chance (EPSS)
- 0.42%
- Chance of exploitation in the next 30 days. Higher than 36.64% of scored vulnerabilities.
- Known exploited
- No
- Not in CISA's catalog
- Weakness
- CWE-1321 Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')
- Fix
4.1.1- Upgrade js-yaml to this version or later
Description
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
Affected versions
npm
| Package | Vulnerable | Fixed in |
|---|---|---|
| js-yaml | >= 4.0.0, < 4.1.1 |
4.1.1 |
| js-yaml | < 3.14.2 |
3.14.2 |
| js-yaml | >= 4.0.0, < 4.1.1 |
4.1.1 |
| js-yaml | < 3.14.2 |
3.14.2 |
How to fix
Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.
js-yaml npm → 4.1.1
- npm
npm install js-yaml@4.1.1- yarn
yarn add js-yaml@4.1.1- pnpm
pnpm add js-yaml@4.1.1
Severity breakdown
CVSS 3.1 5.3
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- Low
- Availability
- None
Weakness
CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')
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.
How to prevent it
- Implementation: By freezing the object prototype first (for example, Object.freeze(Object.prototype)), modification of the prototype becomes impossible.
- Architecture and Design: By blocking modifications of attributes that resolve to object prototype, such as proto or prototype, this weakness can be mitigated.
- Implementation: When handling untrusted objects, validating using a schema can be used.
- Implementation: By using an object without prototypes (via Object.create(null) ), adding object prototype attributes by accessing the prototype via the special attributes becomes impossible, mitigating this weakness.
- Implementation: Map can be used instead of objects in most cases. If Map methods are used instead of object attributes, it is not possible to access the object prototype or modify it.
References
Advisories
Fixes and patches
Packages
Other links
Timeline
- Published
- Last updated by the source
- Latest EPSS score
Related advisories
| Advisory | Severity | Why it's related |
|---|---|---|
| GHSA-r3ph-w7gj-g6xm js-yaml: maxTotalMergeKeys does not limit CPU use for empty merge sources | Medium | Also affects js-yaml |
| GHSA-2883-xcg3-v3hh js-yaml: maxTotalMergeKeys does not limit CPU use for empty merge sources | High | Also affects js-yaml |
| GHSA-5p4m-2wfm-xmqj JS-YAML: Quadratic CPU consumption in !!omap resolution (3.x and 4.x) — CVE-2026-59870 fix not backported | High | Also affects js-yaml |
| GHSA-pm4m-ph32-ghv5 js-yaml: Exponential parsing time in flow collections leads to denial of service | High | Also affects js-yaml |
| GHSA-724g-mxrg-4qvm js-yaml: Quadratic-complexity (O(n^2)) DoS via !!omap tag in YAML11_SCHEMA | High | Also affects js-yaml |
| GHSA-52cp-r559-cp3m js-yaml: YAML merge-key chains can force quadratic CPU consumption | High | Also affects js-yaml |
| GHSA-g796-fgmg-93mv js-yaml: YAML merge-key chains can force quadratic CPU consumption in js-yaml | High | Also affects js-yaml |
| GHSA-h67p-54hq-rp68 JS-YAML: Quadratic-complexity DoS in merge key handling via repeated aliases | Medium | Also affects js-yaml |
Credits: Zephkek, alexstrive, jlp-craigmorten, mhassan1, opal-visibuild, turi4200
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