The Music Sheet Viewer plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the plugin's 'pn_msv' shortcode in all versions up to, and including, 4.1 due to insufficient input sanitization and output escaping on user supplied attributes. 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.
The Music Sheet Viewer plugin for WordPress is vulnerable to Arbitrary File Read in all versions up to, and including, 4.1 via the read_score_file() function. This makes it possible for unauthenticated attackers to read the contents of arbitrary files on the server, which can contain sensitive information.