@phun-ky/defaults-deep Has a Prototype Pollution issue via Unsafe Recursive Property Merging

Exploitation

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

CVSS

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

EPSS

• CVE-2026-54737: 0.46% estimated exploitation activity in the next 30 days; percentile 39.50 (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 A prototype pollution vulnerability exists in @phun-ky/defaults-deep prior to version 2.0.5. The library recursively merged user-supplied objects without filtering unsafe property names such as proto, constructor, and prototype. An attacker able to supply crafted input could cause properties to be written to Object.prototype, resulting in prototype pollution affecting all objects within the running process. Applications that pass untrusted input to defaultsDeep() may be impacted. Depending on how the application uses merged objects, this could lead to unexpected behavior, logic bypasses, denial of service, or other security issues. Patches This issue has been fixed in version 2.0.5. Users should upgrade to version 2.0.5 or later. The fix prevents unsafe prototype-related keys (proto, constructor, and prototype) from being processed during recursive merge operations and includes regression tests covering known prototype pollution vectors. Workarounds Users unable to upgrade…

Published by the source

31 Jul 2026, 17:49 UTC

Last modified by the source

31 Jul 2026, 17:49 UTC

Source last checked

26 Oct 2026, 13:00 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-mj3g-7xcc-x4vh

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# Patch Next advisory brief: CVE-2026-54737

Advisory: @phun-ky/defaults-deep Has a Prototype Pollution issue via Unsafe Recursive Property Merging
IDs: CVE-2026-54737, GHSA-mj3g-7xcc-x4vh
Record: https://patchnext.com/advisories/cve-2026-54737 (revision 1, source checked 26 Oct 2026, 13:00 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: @phun-ky/defaults-deep 2.0.5. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm @phun-ky/defaults-deep: affected < 2.0.5; fixed in 2.0.5

## Suggested inspection (read-only)
- `npm ls @phun-ky/defaults-deep --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 @phun-ky/defaults-deep.
- 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://github.com/advisories/GHSA-mj3g-7xcc-x4vh (GitHub-reviewed advisory GHSA-mj3g-7xcc-x4vh lists affected ranges: npm @phun-ky/defaults-deep >=0 <2.0.5)

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