Deactivated users that had either enrolled via OAuth/SAML or had their account connected to an OAuth/SAML account can still partially access authentik even if their account is deactivated. They end up in a half-authenticated state where they cannot access the API but crucially they can authorize applications if they know the URL of the application.
Several API endpoints can be accessed by users without correct authentication/authorization. The main API endpoints affected by this: /api/v3/crypto/certificatekeypairs/<uuid>/view_certificate/ /api/v3/crypto/certificatekeypairs/<uuid>/view_private_key/ /api/v3/…/used_by/ Note that all of the affected API endpoints require the knowledge of the ID of an object, which especially for certificates is not accessible to an unprivileged user. Additionally the IDs for most objects are UUIDv4, meaning they are not easily guessable/enumerable.
PKCE is a very important countermeasure in OAuth2 , both for public and confidential clients. It protects against CSRF attacks and code injection attacks. Because of this bug, an attacker can circumvent the protection PKCE offers.