Plane is an open-source project management tool. Prior to 1.4.0, the GraphQL joinProject mutation lets any workspace member add themselves to any project in that workspace including network=0 (secret/private) projects they were never invited to and grants them a full Member role (read + write). The resolver checks only workspace-level membership/role and never checks the target project's visibility (network). This collapses project-level tenant isolation within a workspace: a low-privilege member can read and modify confidential data in every private project. This issue is fixed in 1.4.0.