Impact

A user invited via email to a forum with must_approve_users enabled is going to be automatically logged in bypassing the check that does not allow unapproved users to sign in. They will be able to do everything an approved user can do. If they logout, they cannot log in back.

Patches

This issue is patched in the latest stable, beta and tests-passed versions of Discourse.

Workarounds

Disable invites. Administrators can increase min_trust_level_to_allow_invite to reduce the attack surface to more trusted users (e.g. trust level 4).

References

https://meta.discourse.org/t/invite-redemption-allowed-user-to-access-forum-before-approval/214328

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