Magazine Blocks < 1.8.7 - Authenticated (Contributor+) Stored Cross-Site Scripting via 'clientId' Block Attribute

Description

The Magazine Blocks plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the News Ticker block's clientId attribute in versions up to, and including, 1.8.6. This is due to insufficient input sanitization and output escaping in the NewsTicker::render() method, which concatenates the clientId block attribute into an HTML class attribute without applying 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.