Prototype pollution via unsanitized assign keys

Prototype pollution in ts-fns 13.1.3 and earlier allows attackers to modify Object.prototype through crafted assign keys. The assign function treats attacker-controlled dotted property paths such as proto.injectedProp as ordinary deep-assignment targets, so its write reaches the global Object prototype. Exposure requires a consuming application to pass attacker-controlled keys into assign; inherited properties can then corrupt validation state, change application behavior, or crash the process.