AIKIDO-2026-10707

TL;DR

Object schemas that define a catchall merge unrecognized keys onto the parsed output through an internal catchall path. That path treated a literal __proto__ key like a normal property and assigned catchall results onto the output using ordinary property assignment, which can replace the result object's prototype so attacker-supplied keys appear as inherited properties on validated objects. The correction skips that key before running catchall validation so prototype reassignment through this mechanism cannot occur.