defaults-deep CVE-2018-16486
Prototype Pollution in defaults-deep via constructor.prototype.
The problem
defaults-deep <= 0.2.4 (all published versions) is affected by
CVE-2018-16486 (CWE-1321 Prototype Pollution). The published package has
no fix available — exactly what npm audit reports. `defaults-deep` recursively copies source properties into a target. The published version guards against a literal `__proto__` key but still recurses through `constructor` into `constructor.prototype`, allowing an attacker-controlled source object (e.g. parsed from untrusted JSON) to add or overwrite properties on `Object.prototype` for the whole process.
The fix — drop-in, no code changes
Add an overrides entry so every direct and transitive dependency on
defaults-deep resolves to the patched fork, then reinstall:
{
"overrides": {
"defaults-deep": "npm:@keep-lts/defaults-deep@^0.2.5"
}
}Equivalent for Yarn: use resolutions. The public API is unchanged — nothing else to do.
✓ Live on npm: @keep-lts/defaults-deep · or install directly: npm i @keep-lts/defaults-deep
This is rarely the only one
If defaults-deep turned up in your npm audit, there are very likely other abandoned dependencies in the same tree whose CVEs also have no fix on npm. Send us your npm audit output — or your Snyk / Dependabot list — and we'll tell you, for free, which of those findings we already fix. No call, no obligation.
Mid-audit and need a vendor on the hook? Keep LTS Pro adds an SLA on future CVEs and the SBOM / VEX artefacts your auditor will accept — all async, no calls.
What we changed
Keys that name a prototype slot (`__proto__`, `constructor`, `prototype`) are skipped during the recursive merge, so no source data can reach `Object.prototype`. Legitimate deep-default behavior is unchanged — real configuration data does not contain these reserved section names.
Proof of concept (the vulnerability)
const defaultsDeep = require('defaults-deep');
defaultsDeep({}, JSON.parse('{"constructor":{"prototype":{"polluted":"yes"}}}'));
console.log(({}).polluted); // => 'yes' (Object.prototype polluted)@keep-lts/defaults-deep@0.2.5How we keep it trustworthy
- Minimal, surgical patch — security only, no feature changes.
- A regression test that fails on the original and passes on the patch; legitimate behaviour preserved.
- Published under the
@keep-ltsorg with the full advisory and tests inside the package; upstream license & attribution retained.
Full advisory and changelog ship inside the package (SECURITY.md, CHANGELOG.md).