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CVE-2026-54737 high CVSS 7.3

Vulnerability in @phun-ky/defaults-deep (CVE-2026-54737)

Summary

Vulnerability in @phun-ky/defaults-deep (CVE-2026-54737). Risk of unauthorized operations or information disclosure. Exploitable via __proto__. Mitigation: upgrade to 2.0.5 or later.

Original description

The description as published by the source.

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 should ensure that untrusted input is sanitized before being passed to defaultsDeep().

At a minimum, applications should reject or remove the following property names from all levels of user-controlled objects:

  • __proto__
  • constructor
  • prototype

Upgrading to a patched version remains the recommended mitigation.

Source: GitHub Security Advisories (Global) NVD GitHub Advisory

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2026-54737 has been found in @phun-ky/defaults-deep.
Attackers can target a specific entry point like __proto__ over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 7.3/10.
What to do: upgrade @phun-ky/defaults-deep to 2.0.5 or later.
If unsure, ask your IT team or search "@phun-ky/defaults-deep CVE-2026-54737" on the vendor's site.

CVE-2026-54737 (@phun-ky/defaults-deep) — CWE-1321 / CVSS v3 7.3
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: __proto__ / constructor / prototype / Object.prototype
Patched: 2.0.5 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

A vulnerability (CWE-1321) exists in @phun-ky/defaults-deep. Attackers reach the vulnerable code path via __proto__ without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of @phun-ky/defaults-deep. Attack surface: __proto__ / constructor / prototype / Object.prototype.

🔥 Severity

Severity: High (CVSS 7.3/10). Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 2.0.5.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r '@phun-ky/defaults-deep' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

  1. 1
    Identify exposure identify 
    grep -r '@phun-ky/defaults-deep' . | grep -v node_modules

    リポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で @phun-ky/defaults-deep を grep し、稼働しているサービス・バージョンを把握する。

  2. 2
    Apply patch patch 
    Upgrade @phun-ky/defaults-deep to 2.0.5

    ステージング環境で 2.0.5 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。

  3. 3
    Post-deployment verification verify 
    Confirm patched version is live in production

    パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

npm @phun-ky/defaults-deep
[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"2.0.5"}]}]

References

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