Symptoms
Users with ITIL role are able to create articles and how to block these users from creating new articles.
Cause
Create ACLs on kb_knowledge
Resolution
You can achieve this by modifying the create ACLs on Knowledge (kb_knowledge) table. You can add roles so that ITIL users are not included in that or you could add a script within the ACL to check if the user has an ITIL role and block the user.