Newsletters < 4.16 - Authenticated (Contributor+) Stored Cross-Site Scripting via 'target' Shortcode Attribute

Description

The Newsletters Lite plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'target' attribute of the [newsletters_post] shortcode in versions up to and including 4.15. This is due to insufficient input sanitization and output escaping in the posts_single() function which propagates the attacker-controlled 'target' attribute into the global $wpml_target, and in the shortcode_posts() 'post_thumbnail' handler which concatenates $wpml_target into a target="..." HTML attribute without esc_attr(). 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.