AIKIDO-2026-500926

TL;DR

Object and record parsers did not consistently strip a __proto__ key. The key could still be copied from untrusted input, declared on the schema, or produced when a record key schema or transform normalized a value to __proto__, which can replace the parsed object's prototype via ordinary property assignment. .strict() also swallowed an own __proto__ input key instead of reporting unrecognized_keys. Error formatters and both JSON Schema converters wrote nested path segments such as toString or constructor without own-property semantics, so those segments could walk onto Object.prototype. Parsers now drop __proto__ in all of those cases, .strict() reports the key, and formatters and converters use own-property writes.