Improper Neutralization of Invalid Characters in Identifiers in Web Pages

Modern web browsers often interpret malformed identifiers in unexpected ways. For instance, a browser might silently strip out null bytes or other invalid characters, reconstructing a dangerous payload that the developer's filters missed. This creates a gap where your security checks see a harmless string, but the browser executes it as active code. Attackers exploit this by embedding these invalid sequences—like null bytes or alternative encodings—within identifiers such as URI schemes. A common bypass involves encoding "javascript:" as something like `java%00script:`, which might bypass a simple blacklist filter but still render as executable JavaScript in the browser, leading to cross-site scripting (XSS) or other client-side attacks.