Improper Neutralization of Alternate XSS Syntax

Traditional XSS defenses often focus on blocking common vectors like `<script>` tags or basic event handlers. However, attackers can bypass these filters by using less common syntax, encoding techniques, or obscure HTML attributes that browsers still interpret as executable code. This includes alternative event handlers, JavaScript pseudo-protocols in unexpected places, or creatively malformed tags that slip past validation routines. To prevent this, developers must adopt a positive security model that defines allowed input, rather than just blocking known bad patterns. Input validation should be combined with context-aware output encoding, ensuring user data is treated as text, not code, regardless of the syntax used. Regular security testing with tools that probe for these alternate vectors is essential for robust defense.