The vulnerability stems from two unescaped outputs: 1) The user-controllable TOC title specified in @toc syntax, and 2) Header text used in anchor links. In markdown-it plugin architecture, these would be handled by the TOC rendering function and header parsing logic respectively. Without proper HTML entity escaping (e.g., using markdown-it's built-in escapeHtml utility), user input flows directly into HTML output. The high confidence comes from the vulnerability description explicitly identifying these two injection points and the package's failure to implement standard XSS protections in these contexts.