The Easy Prism Syntax Highlighter plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the plugin's 'code' (and 'c') shortcode in versions up to, and including, 1.0.2. This is due to insufficient input sanitization and output escaping on user supplied shortcode attributes in the shortcode() function, which concatenates the first positional attribute directly into the class attribute of the generated <pre>/<code> HTML without calling esc_attr() or any other escaping function. This makes it possible for authenticated attackers, with contributor-level access and above, to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page.