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GHSA-4c35-wcg5-mm9h: next-intl has prototype pollution with `experimental.messages.precompile` via attacker-controlled translation catalog keys

May 6, 2026

setNestedProperty in packages/next-intl/src/extractor/utils.tsx walks a dotted key path and assigns the final value without blocking the reserved keys __proto__, constructor, or prototype. When the next-intl Next.js plugin is configured with experimental.messages and messages.precompile: true, a JSON translation catalog containing a top‑level __proto__ key causes setNestedProperty(result, '__proto__.isAdmin', compiledMessage) to assign onto Object.prototype, polluting every object in the running build process.

References

  • github.com/advisories/GHSA-4c35-wcg5-mm9h
  • github.com/amannn/next-intl/security/advisories/GHSA-4c35-wcg5-mm9h

Code Behaviors & Features

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Affected versions

All versions before 4.9.2

Fixed versions

  • 4.9.2

Solution

Upgrade to version 4.9.2 or above.

Impact 4.2 MEDIUM

CVSS:3.1/AV:L/AC:H/PR:L/UI:R/S:U/C:L/I:L/A:L

Learn more about CVSS

Weakness

  • CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')

Source file

npm/next-intl/GHSA-4c35-wcg5-mm9h.yml

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