The Passster – Password Protect Pages and Content plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'metavalue (metakeyinput=passster_id | passster_headline)' parameter in all versions up to, and including, 4.3.21 due to insufficient input sanitization and output escaping. 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. A Contributor can break out of the shortcode attribute context by embedding a ] character in the passster_id or passster_headline meta value to prematurely close the opening shortcode tag, then append a [/passster] closing tag so that the trailing HTML payload is emitted verbatim by do_shortcode() — bypassing the per-attribute escaping present inside render_shortcode() — and the script will also execute in an editor's or administrator's browser when they preview the Contributor's pending post, since filter_the_content() has no edit-permission capability gate.
Attack Parameters
Impact Assessment
CVSS Vector v3.1