aBlocks <= 2.17.0 - Authenticated (Contributor+) Privilege Escalation to 'roleSlug' Block Attribute

The aBlocks – Gutenberg Blocks, User Dashboard Builder, Popup Builder, Form Builder & Animation Builder plugin for WordPress is vulnerable to Privilege Escalation in all versions up to, and including, 2.17.0 via the `/ablocks/v1/form-builder/registration` REST endpoint. The vulnerability exists because the endpoint is registered with `permission_callback => __return_true` and the `register()` handler reads `roleSlug` directly from attacker-controlled block attributes in `post_content` without ever verifying that the block's `formType` is `registration` — a condition that `RegistrationFormSanitizer::verify()` imposes only at save-time, meaning a Contributor can preserve an arbitrary `roleSlug` by saving a block with `formType='login'` and then triggering the endpoint via a valid `wp_rest` nonce and post-ownership check. This makes it possible for authenticated attackers, with Contributor-level access and above, to escalate their WordPress role to Editor or any other non-administrator role and receive a fully authenticated session at the elevated privilege level via `WP_User::set_role()` and `wp_set_auth_cookie()`. Escalation is bounded below administrator-tier roles because `is_safe_registration_role()` rejects any role holding `manage_options`, `edit_users`, `delete_users`, `create_users`, `promote_users`, or `edit_theme_options`, meaning the highest practically reachable role on a standard WordPress installation is Editor.

CVSS vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

CWE: CWE-269