Vikunja is an open-source self-hosted task management platform. Prior to version 2.2.1, when the Vikunja API returns tasks, it populates the `related_tasks` field with full task objects for all related tasks without checking whether the requesting user has read permission on those tasks' projects. An authenticated user who can read a task that has cross-project relations will receive full details (title, description, due dates, priority, percent completion, project ID, etc.) of tasks in projects they have no access to. Version 2.2.1 patches the issue.

Affected: Go: code.vikunja.io/api

## Summary

When the Vikunja API returns tasks, it populates the `related_tasks` field with full task objects for all related tasks without checking whether the requesting user has read permission on those tasks' projects. An authenticated user who can read a task that has cross-project relations will receive full details (title, description, due dates, priority, percent completion, project ID, etc.) of tasks in projects they have no access to.

## Details

The vulnerability is in `addRelatedTasksToTasks()` at `pkg/models/tasks.go:496-548`. This function is called by `addMoreInfoToTasks()` (line 773) during every task read operation — both project task listings (`GET /api/v1/projects/{id}/views/{id}/tasks`) and single task reads (`GET /api/v1/tasks/{id}`).

The function fetches all related tasks directly from the database without any permission filtering:

```go // pkg/models/tasks.go:496-548 func addRelatedTasksToTasks(s *xorm.Session, taskIDs []int64, taskMap map[int64]*Task, a web.Auth) (err error) { relatedTasks := []*TaskRelation{} err = s.In("task_id", taskIDs).Find(&relatedTasks) // ... fullRelatedTasks := make(map[int64]*Task) err = s.In("id", relatedTaskIDs).Find(&fullRelatedTasks) // Line 514: NO permission check // ... for _, rt := range relatedTasks { // Directly adds to response without checking if user can read the related task taskMap[rt.TaskID].RelatedTasks[rt.RelationKind] = append( taskMap[rt.TaskID].…