Vikunja before 2.7.1 Memory Exhaustion DoS via Trello, Todoist and Microsoft To Do Migrations

Vikunja before 2.7.1 allocates memory without limits in its Trello, Todoist and Microsoft To Do migration importers, which buffer remote attachment downloads and API responses in memory without size caps. Authenticated users can start a migration that references huge attacker-served attachments or yields oversized API responses, exhausting memory and crashing the shared API process for all tenants.