Modification of Assumed-Immutable Data (MAID) vulnerability in Hapijs Hoek hoek node module before 4.2.0 and 5.0.x before 5.0.3 suffers from a Modification of Assumed-Immutable Data (MAID) vulnerability via 'merge' and 'applyToDefaults' functions, which allows a malicious user to modify the prototype of "Object" via __proto__, causing the addition or modification of an existing property that will exist on all objects.