fix(zod): prevent prototype injection in smart coercion#1727
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`ZodSmartCoercionPlugin` and `experimental_ZodSmartCoercionPlugin`
collected coerced object and record properties into a plain `{}`, so an
input key named `__proto__` hit the `Object.prototype` setter instead of
creating an own property.
They also looked up sub-schemas with `shape[key]`, which resolves
`constructor`, `toString` and `__proto__` through `Object.prototype`.
Those inherited values were then dereferenced as Zod schemas and threw a
`TypeError`, so any request carrying such a key failed coercion.
Collect into `NullProtoObj` and guard the lookup with `Object.hasOwn`.
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Same two prototype chain bugs as #1726, in
ZodSmartCoercionPlugin(zod 3) andexperimental_ZodSmartCoercionPlugin(zod 4). Both plugins coerce untrusted input before validation, so the keys below are attacker controlled.1. Coerced properties were collected into a plain
{}newObj['__proto__'] = valuetriggers the inherited__proto__setter instead of creating an own property. This affects theobjectandrecordbranches in both plugins.Fix: collect into
NullProtoObj, the helper already used for untrusted keys inbracket-notation.tsandrpc-matcher.ts.2.
shape[key]returned inherited membersFor keys like
constructor,toStringand__proto__the lookup resolves toObject.prototypemembers, which were then dereferenced as Zod schemas:The throw happens before the assignment, so in practice these keys made coercion fail rather than injecting a prototype. Any client could break a request this way.
Fix: guard the lookup with
Object.hasOwn, so unknown keys fall through tocatchallas they already do for every other name.Verification
zodSmartCoercionPlugin prevents prototype injectionadded to both test files, coveringobject,recordandcatchall. Both fail without the fix. The zod coercer suites pass (583 tests).tsc -band eslint are clean.