GHSA-564f-wx8x-878h Vikunja read-only users can delete project background images via broken object-level authorization

• Go code.vikunja.io/api: >= 0.20.2, < 2.2.0 → fixed in 2.2.0

Summary The `DELETE /api/v1/projects/:project/background` endpoint checks `CanRead` permission instead of `CanUpdate`, allowing any user with read-only access to a project to permanently delete its background image. Details The `RemoveProjectBackground` handler (`pkg/modules/background/handler/background.go`) reuses `checkProjectBackgroundRights`, a helper originally written for the read-only `GetProjectBackground` endpoint. This helper only verifies `CanRead` permission. In contrast, the handler for *setting* a background (`setBackgroundPreparations`) correctly checks `CanUpdate`. As a result, destructive write operations (deleting the background file from storage and clearing the project's `background_file_id` and `background_blur_hash` fields) are gated behind a read-only permission check. Impact A user with read-only access to a project — via direct sharing, team membership, link share tokens with read permission, or read-scoped API tokens — can permanently delete the project's background image. The background file is removed from storage and cannot be recovered. This constitutes unauthorized data destruction. Reproduction 1. User A creates a project and sets a background image. 2. User A shares the project with User B with read-only permission. 3. User B sends: `DELETE /api/v1/projects/{project_id}/background` with a valid auth token. 4. The request succeeds. The background image is permanently deleted. References • `pkg/modules/background/handler/background.go` — `RemoveProjectBackground` (line 416), `checkProjectBackgroundRights` (line 304), `setBackgroundPreparations` (line 106) • `pkg/routes/routes.go` line 665 — route registration Credits This vulnerability was found using GitHub Security Lab Taskflows.