Zulip is an open-source team collaboration tool

Zulip is an open-source team collaboration tool. From 8.0 until 12.2, in organizations where the Who can view all other users in the organization setting restricted guests from viewing other users, saving or editing a direct message draft did not verify that the sender could access the draft recipients. A guest could thereby gain access to otherwise restricted users' profile information without sending a message. Organizations that did not restrict guest access were unaffected. This issue is fixed in version 12.2.