The Advanced Custom Fields (ACF) plugin for WordPress is vulnerable to Stored Cross-Site Scripting via a custom text field in all versions up to, and including, 6.2.4 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.
https://www.advancedcustomfields.com/blog/acf-6-2-5-security-release/
https://plugins.trac.wordpress.org/changeset/3022469/advanced-custom-fields