Node.js CVE-2026-33863

Impact

Two unguarded prototype pollution paths exist, not covered by previous fixes:

1. config.load() / config.loadFile() - overlay() recursively merges config data without checking for forbidden keys. Input containing __proto__ or constructor.prototype (e.g. from a JSON file) causes the recursion to reach Object.prototype and write attacker-controlled values onto it.
2. Schema initialization - passing a schema with constructor.prototype.* keys to convict({...}) causes default-value propagation to write directly to Object.prototype at startup.

Depending on how polluted properties are consumed, impact ranges from unexpected behavior to authentication bypass or RCE.

Workarounds

Do not pass untrusted data to load(), loadFile(), or convict().

Resources

Prior advisory: GHSA-44fc-8fm5-q62h Related issue: https://github.com/mozilla/node-convict/issues/423