Mutation-Based XSS - The Emerging Threat

A newer category worth understanding is mutation-based XSS (mXSS), which exploits the way browsers parse and re-serialize HTML. These attacks rely on browser quirks where seemingly safe HTML mutates into dangerous code during processing. For example, certain combinations of HTML entities and tags might be modified by the browser's parser in ways that create executable scripts. This type of XSS is particularly challenging because the payload might pass all server-side and client-side filters in its original form, only becoming dangerous after browser processing.