Advanced Custom Fields <= 6.3.8 - Authenticated (Admin+) Limited Arbitrary Function Call

The Advanced Custom Fields (ACF) plugin for WordPress is vulnerable to limited arbitrary function calls via the 'register_meta_box_cb' and 'meta_box_cb' parameters in all versions up to, and including, 6.3.8 (excluding 6.3.6.2) due to insufficient input validation on those parameters. This makes it possible for authenticated attackers, with administrator-level access, to inject arbitrary functions, like WordPress functions, in custom post types that will execute whenever a user accesses the injected post type. This can be leveraged to trick other users like administrators accessing posts into performing unauthorized actions through functions, and is not a very serious risk for the vast majority of site owners. Please follow the reference listed in this vulnerability record for instructions on how to update to the latest version of ACF that patches this issue and ensures accessibility to updates moving forward. Please note this issue was partially patched in 6.3.8 and 6.3.6.1 - 6.3.6.2, however, was hardened further in 6.3.6.3 and 6.3.9.