Moodle OpenAI Chat Block plugin 3.0.1 (2025021700) suffers from an Insecure Direct Object Reference (IDOR) vulnerability due to insufficient validation of the blockId parameter in /blocks/openaichat/api/completion.php. An authenticated student can impersonate another user's block (e.g., administrator) and send queries that are executed with that block's configuration. This can expose administrator-only Source of Truth entries, alter model behavior, and potentially misuse API resources.