In Episode 49 of the Melapress Show, Matthew Rollings, application security professional and bug bounty hunter, joins Robert Abela to break down RegexXSS: a vulnerability class hiding in the regex code of WordPress plugins. Mat explains how post-sanitization regex manipulation can reintroduce cross-site scripting even after WordPress has done its job, and demonstrates how an attacker can leverage it to take over a full admin account.

Many developers are unaware that using regex to parse or modify HTML, even after WordPress's built-in KSES sanitization, can introduce fresh XSS vectors. With over 70,000 WordPress plugins in existence, and regex used heavily throughout PHP development, this vulnerability class is both widespread and chronically under-reported. Mat has earned £20–30k in bug bounties from this single class alone.

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