Update devDependency defu to v6.1.5 [SECURITY]

[renovate]

This PR contains the following updates:

Package	Change	Age	Confidence
defu	6.1.4 → 6.1.5

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defu: Prototype pollution via __proto__ key in defaults argument

CVE-2026-35209 / GHSA-737v-mqg7-c878

More information

Details

Impact

Applications that pass unsanitized user input (e.g. parsed JSON request bodies, database records, or config files from untrusted sources) as the first argument to defu() are vulnerable to prototype pollution.

A crafted payload containing a __proto__ key can override intended default values in the merged result:

import { defu } from 'defu'

const userInput = JSON.parse('{"__proto__":{"isAdmin":true}}')
const config = defu(userInput, { isAdmin: false })

config.isAdmin // true — attacker overrides the server default

Root Cause

The internal _defu function used Object.assign({}, defaults) to copy the defaults object. Object.assign invokes the __proto__ setter, which replaces the resulting object's [[Prototype]] with attacker-controlled values. Properties inherited from the polluted prototype then bypass the existing __proto__ key guard in the for...in loop and land in the final result.

Fix

Replace Object.assign({}, defaults) with object spread ({ ...defaults }), which uses [[DefineOwnProperty]] and does not invoke the __proto__ setter.

Affected Versions

<= 6.1.4

Credits

Reported by @​BlackHatExploitation

Severity

• CVSS Score: 7.5 / 10 (High)
• Vector String: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

References

• https://github.com/unjs/defu/security/advisories/GHSA-737v-mqg7-c878
• https://nvd.nist.gov/vuln/detail/CVE-2026-35209
• https://github.com/unjs/defu/pull/156
• https://github.com/unjs/defu/commit/3942bfbbcaa72084bd4284846c83bd61ed7c8b29
• https://github.com/unjs/defu/releases/tag/v6.1.5
• https://github.com/advisories/GHSA-737v-mqg7-c878

This data is provided by the GitHub Advisory Database (CC-BY 4.0).

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Release Notes

unjs/defu (defu)

v6.1.5

Compare Source

compare changes

🩹 Fixes

• Prevent prototype pollution via __proto__ in defaults (#​156)
• Ignore inherited enumerable properties (11ba022)

🏡 Chore

• Add tea.yaml (70cffe5)
• Update repo (23cc432)
• Fix typecheck (89df6bb)

✅ Tests

• Add more tests for plain objects (b65f603)

🤖 CI

• Bump node (9237d9c)

❤️ Contributors

• Pooya Parsa (@​pi0)
• Kricsleo (@​kricsleo)

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Project	Deployment	Actions	Updated (UTC)
ungh	Ready	Preview, Comment	Jun 2, 2026 12:38am