The vulnerability stems from unsanitized filename handling in two key areas: 1) When serving files directly, filenames containing XSS payloads would be reflected in Content-Disposition headers or error messages. 2) When generating directory listings, filenames are embedded in HTML without proper escaping. These patterns match common static server implementations, and the vulnerability description explicitly mentions filename sanitization failures as the root cause. While exact code isn't available, these functions represent standard points of vulnerability for XSS in file-serving applications.