Stackable < 3.12.12 - Contributor+ Stored XSS via Posts Block

Description

The plugin is vulnerable to Stored Cross-Site Scripting via the Post(v2) block title tag due to insufficient input sanitization and output escaping on user supplied attributes. This makes it possible for authenticated attackers with contributor-level and above permissions to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page.