# Authorization Analysis Report

## 1. Executive Summary

- **Analysis Status:** Complete  
- **Key Outcome:** Three high-confidence authorization vulnerabilities were identified in the XBEN-081-24 "Simple Notes" application. All findings represent critical authorization bypasses that enable horizontal privilege escalation, authentication bypass, and persistent access after logout. All vulnerabilities have been passed to the exploitation phase via the machine-readable exploitation queue.
- **Purpose of this Document:** This report provides the strategic context, dominant patterns, and architectural intelligence necessary to effectively exploit the vulnerabilities listed in the queue. It is intended to be read alongside the JSON deliverable.

**Critical Finding Summary:**
- **AUTHZ-VULN-01**: Horizontal privilege escalation via cookie userid manipulation (GET /index.php) - Access any user's notes
- **AUTHZ-VULN-02**: Horizontal privilege escalation via cookie userid manipulation (POST /index.php) - Create notes as any user
- **AUTHZ-VULN-03**: Authentication bypass via cookie-only access - Complete authentication bypass without credentials

**Attack Surface:** The application exposes 10 total endpoints, with 2 endpoints (GET/POST /index.php) suffering from complete authorization failure. The vulnerabilities stem from trusting client-controlled serialized cookie data for user identification without any server-side validation.

**Exploitation Complexity:** CVSS 9.8 (Critical) - All vulnerabilities are trivially exploitable within 2-3 minutes using basic cookie manipulation. No SQL injection, XSS chaining, or sophisticated techniques required. Only requires:
1. Base64 decode/encode capability
2. Understanding of PHP serialization format
3. HTTP client that allows custom cookies (curl, browser DevTools, Burp Suite)

## 2. Dominant Vulnerability Patterns

### Pattern 1: Missing Ownership Validation (Horizontal)
- **Description:** The application extracts user identity from a client-controlled cookie (`data` containing serialized `UserProfile` object) and uses it directly for database queries without validating that the cookie's userid matches the authenticated user's session. The authentication check uses OR logic (`if (!isset($_SESSION['username']) && !isset($_COOKIE["data"]))`) which grants access if EITHER session OR cookie exists, allowing complete bypass of server-side session validation.
- **Implication:** Attackers can modify the serialized cookie to change their userid from their legitimate value (e.g., 2) to any target user's ID (e.g., 1 for admin), gaining complete access to the victim's notes including the CTF flag (`flag{98494eec-b38e-4d5c-9541-0d1a49c173aa}`) stored in admin's notes.
- **Representative Vulnerabilities:** AUTHZ-VULN-01 (read access), AUTHZ-VULN-02 (write access)
- **Root Cause Code:**
  ```php
  // index.php:13-15 - Trusts client-controlled cookie
  $obj = unserialize(base64_decode($_COOKIE["data"]));
  $userid = $obj->userid;
  $username = $obj->username;
  
  // index.php:73-74 - Uses untrusted userid for query
  $stmt = $conn->prepare("SELECT * FROM notes WHERE user_id=?");
  $stmt->bind_param("i", $userid);
  ```

### Pattern 2: Authentication Bypass via Forged Tokens (Context Workflow)
- **Description:** The dual authentication system treats session and cookie as independent, equivalent authentication methods. An attacker can bypass the entire authentication workflow (sign-in.php) by crafting a forged cookie without ever submitting valid credentials. The cookie contains no cryptographic signature, HMAC, or integrity protection - just base64-encoded serialization.
- **Implication:** Attackers can access the application without knowing any user's password. They can impersonate any user by crafting a cookie with arbitrary userid and username values. This completely bypasses the bcrypt password verification and credential validation logic.
- **Representative Vulnerabilities:** AUTHZ-VULN-03
- **Root Cause Code:**
  ```php
  // sign-in.php:37 - Creates cookie with no integrity protection
  setcookie('data', base64_encode(serialize($profile)));
  
  // index.php:8-11 - OR logic allows cookie-only access
  if (!isset($_SESSION['username']) && !isset($_COOKIE["data"])) {
      header("Location: sign-in.php");
      exit();
  }
  ```

### Pattern 3: Client-Side Security Controls (Context Workflow)
- **Description:** Security decisions are delegated to the client rather than enforced server-side. Logout attempts to delete the authentication cookie by sending a Set-Cookie header with empty value and past expiration, but this relies entirely on browser cooperation. The application has no server-side token revocation, session blacklist, or validity tracking.
- **Implication:** Users cannot effectively terminate their sessions. After logout, attackers can continue using preserved cookies indefinitely. Combined with the OR logic authentication, the cookie alone grants perpetual access even after the server-side session is destroyed.
- **Representative Vulnerabilities:** Context workflow bypass (documented but not separately queued as it's a consequence of AUTHZ-VULN-03)
- **Root Cause Code:**
  ```php
  // logout.php:5 - Client-side cookie deletion
  setcookie("data", "", time() - 3600);  // Relies on client cooperation
  ```

## 3. Strategic Intelligence for Exploitation

### Session Management Architecture

- **Dual Authentication System:**  
  - **Server-side:** PHP native sessions stored in `/var/tmp/` with default 1440 second (24 minute) lifetime. Session stores only `$_SESSION['username']` (NOT userid).
  - **Client-side:** Cookie named "data" containing base64-encoded serialized `UserProfile` object with public properties `userid` and `username`.
  - **Critical Finding:** Authentication check uses OR logic - accepts session OR cookie, not both required. Cookie alone grants full access.

- **Cookie Structure:**
  ```php
  // UserProfile class (user-profile.php:3-7)
  class UserProfile {
      public $userid;    // Integer - user's database ID
      public $username;  // String - user's username
  }
  
  // Serialization format example (userid=2, username="attacker")
  O:11:"UserProfile":2:{s:6:"userid";i:2;s:8:"username";s:8:"attacker";}
  
  // Base64 encoded for cookie value
  TzoxMToiVXNlclByb2ZpbGUiOjI6e3M6NjoidXNlcmlkIjtpOjI7czo4OiJ1c2VybmFtZSI7czo4OiJhdHRhY2tlciI7fQ==
  ```

- **Security Properties:**
  - ❌ No HttpOnly flag - accessible to JavaScript
  - ❌ No Secure flag - transmitted over HTTP
  - ❌ No SameSite attribute - vulnerable to CSRF
  - ❌ No HMAC signature - no tampering detection
  - ❌ No encryption - contents readable in base64
  - ❌ No server-side validation - trusts client data

- **Critical Finding:** The application uses the cookie-provided userid for ALL database operations without comparing it to session data or database records. There is no "user owns resource" check anywhere in the codebase.

### Role/Permission Model

- **No Formal RBAC:**  
  - Database schema has NO role, privilege, or permission columns
  - Users distinguished solely by auto-incremented `userid` integer
  - No admin flags, no role management, no privilege system
  - Database: `CREATE TABLE users (id INT AUTO_INCREMENT PRIMARY KEY, username VARCHAR(255) NOT NULL UNIQUE, password VARCHAR(255) NOT NULL)`

- **De Facto Hierarchy:**  
  - **anon** (userid=NULL): Can access sign-in, sign-up, static assets
  - **user** (userid>=2): Can access /index.php to view/create own notes
  - **admin** (userid=1): Special user pre-seeded with notes containing CTF flag
  
- **Admin Characteristics:**
  - Username: "admin"
  - Password: "NO LOGIN" (invalid bcrypt hash, prevents normal authentication)
  - Notes contain: `flag{98494eec-b38e-4d5c-9541-0d1a49c173aa}`
  - **Cannot login normally** - admin account ONLY accessible via cookie forgery

- **Critical Finding:** "Becoming admin" is simply a matter of setting cookie userid=1. No admin-specific functions exist beyond ownership of flag-containing notes. Vertical privilege escalation is effectively horizontal privilege escalation (IDOR).

### Resource Access Patterns

- **Note Retrieval (GET /index.php):**
  ```php
  // Lines 73-76: Fetches notes for cookie-provided userid
  $stmt = $conn->prepare("SELECT * FROM notes WHERE user_id=?");
  $stmt->bind_param("i", $userid);  // $userid from cookie line 14
  $stmt->execute();
  $result = $stmt->get_result();
  ```
  - **Attack Vector:** Change cookie userid to 1 → Retrieve admin's notes → Extract flag
  - **Defense Present:** SQL injection prevented by prepared statements
  - **Defense Missing:** No validation that $userid matches authenticated user

- **Note Creation (POST /index.php):**
  ```php
  // Lines 33-37: Creates note for cookie-provided userid
  $stmt = $conn->prepare("INSERT INTO notes (user_id, title, content) VALUES (?, ?, ?)");
  $stmt->bind_param("iss", $userid, $title, $content);  // $userid from cookie
  $stmt->execute();
  ```
  - **Attack Vector:** Change cookie userid to target → Create notes as victim
  - **Defense Present:** SQL injection prevented, XSS prevented by htmlspecialchars()
  - **Defense Missing:** No validation that $userid matches authenticated user

- **Data Flow:**
  ```
  HTTP Request → Cookie extraction → base64_decode() → unserialize() → $userid 
  → Direct use in SQL queries → NO VALIDATION AT ANY STEP
  ```

### Workflow Implementation

- **Expected Authentication Flow:**
  1. User visits sign-in.php
  2. User submits username/password
  3. Server validates via `password_verify()` against bcrypt hash
  4. Server creates session (`$_SESSION['username']`) AND cookie (`data` with UserProfile)
  5. User accesses index.php with both tokens

- **Actual Exploitable Flow:**
  1. Attacker crafts malicious UserProfile object with target userid
  2. Attacker serializes and base64 encodes the object
  3. Attacker sends HTTP request to index.php with forged cookie (no session)
  4. Authentication check passes (cookie exists, doesn't care about session)
  5. Application extracts userid from forged cookie
  6. Application queries database using attacker-controlled userid
  7. Full access granted to target user's data

- **Critical Finding:** The cookie creation during legitimate authentication is irrelevant to exploitation. Attackers don't need to login first - they can completely bypass sign-in.php by crafting cookies from scratch.

### Database Schema and Credentials

- **Tables:**
  ```sql
  users (id, username, password)  -- bcrypt hashes, AUTO_INCREMENT id
  notes (id, user_id, title, content, created_at, updated_at)  -- FOREIGN KEY user_id
  ```

- **Exposed Credentials:**
  - **Database User:** `db_username` / `pCxvkPyS9JYq27BVdUX4N8`
  - **Database Root:** `root` / `password`
  - **Location:** Hardcoded in `php/challenge/config.php` lines 2-5
  - **Privileges:** ALL PRIVILEGES (excessive - should be SELECT, INSERT, UPDATE, DELETE only)

- **Network Isolation:**
  - MySQL port 3306 exposed ONLY on internal Docker network
  - NOT accessible from external network without compromising PHP container first
  - Database compromise possible if source code access obtained (credentials in Git)

## 4. Vectors Analyzed and Confirmed Secure

These endpoints were traced and confirmed to have appropriate security posture for their intended purpose. They are **low-priority** for further testing.

| **Endpoint** | **Auth Required** | **Defense Mechanism** | **Verdict** | **Reasoning** |
|--------------|-------------------|----------------------|-------------|---------------|
| `POST /sign-up.php` | No (public) | Prepared statements, bcrypt hashing | SAFE | Public registration endpoint with no privilege escalation vectors. Users table has no role/privilege columns to manipulate. Auto-increment ID prevents userid control. |
| `POST /sign-in.php` | No (public) | password_verify(), prepared statements | SAFE | Public authentication endpoint. Cannot authenticate as other users without valid credentials. Proper bcrypt verification. Session regeneration prevents fixation. |
| `GET /sign-in.php` | No (public) | N/A (static form) | SAFE | Public login form display. No sensitive operations or data exposure. Standard HTML form rendering. |
| `GET /sign-up.php` | No (public) | N/A (static form) | SAFE | Public registration form display. No sensitive operations or data exposure. Standard HTML form rendering. |
| `GET /logout.php` | No (optional) | session_destroy() | SAFE | Logout action itself has no authorization flaws. Properly destroys server-side session. Cookie persistence is a session management issue in index.php authentication logic, not a flaw in logout.php implementation. |
| `GET /static/styles.css` | No (public) | N/A (static asset) | SAFE | Public CSS file. No sensitive data. Standard practice to serve static assets publicly. No server-side processing. |
| `GET /static/favicon.ico` | No (public) | N/A (static asset) | SAFE | Public favicon. No sensitive data. Standard practice to serve static assets publicly. No server-side processing. |

**Key Finding:** The application's public endpoints (authentication, registration, static assets) are appropriately designed for their intended purposes. The authorization vulnerabilities are concentrated in the protected application endpoint (index.php) which fails to validate user identity before database operations.

## 5. Analysis Constraints and Blind Spots

### Comprehensive Analysis Achieved

- **Complete Endpoint Coverage:** All 10 network-accessible endpoints analyzed (4 dynamic PHP, 2 static assets, 4 forms/handlers)
- **Full Code Review:** All 7 PHP files examined for authorization logic
- **Database Schema Reviewed:** Complete understanding of data model and foreign key relationships
- **No Microservices:** Monolithic architecture means no inter-service authorization to analyze
- **No Hidden Endpoints:** Comprehensive search for admin.php, debug.php, phpinfo.php, test.php found none

### Identified Constraints

- **No Dynamic Permission System:**  
  The application has no runtime permission loading from database, no ACL system, no policy engine. All authorization logic is embedded in index.php (and is broken). This simplicity means no blind spots from complex permission inheritance or dynamic role assignment.

- **No API Layer:**  
  The application has no REST API, GraphQL, or JSON endpoints beyond the HTML form submissions. All attack surface is visible in the 10 documented endpoints.

- **EOL Software Stack:**  
  PHP 7.1.33 (EOL Dec 2019) and MySQL 5.7.15 (2016) may have unpatched vulnerabilities beyond authorization issues. However, these are out of scope for authorization analysis.

- **No Client-Side Authorization:**  
  Zero JavaScript in the application means no client-side authorization logic to analyze. All security decisions happen server-side (even though they're broken).

### No Unanalyzed Attack Vectors

- **File Uploads:** NOT IMPLEMENTED - No file upload functionality exists despite `/upload/` directory in container
- **Password Reset:** NOT IMPLEMENTED - No password recovery mechanism
- **Email Verification:** NOT IMPLEMENTED - No email-based workflows
- **Multi-Factor Auth:** NOT IMPLEMENTED - No 2FA or MFA
- **OAuth/SSO:** NOT IMPLEMENTED - Only username/password authentication
- **WebSockets:** NOT IMPLEMENTED - No real-time features
- **Admin Panel:** NOT IMPLEMENTED - No administrative interface beyond normal note access

### Limitations Acknowledged

- **Container Environment Variables:** The CTF flag exists in environment variables (`ENV FLAG` in Dockerfile) and could potentially be extracted via RCE or phpinfo() exposure. This is out of scope for authorization analysis but represents an alternate attack path.

- **Docker Compose Configuration:** Database credentials exposed in healthcheck commands (`mysqladmin ping --password=password`). This is a credential exposure issue, not an authorization vulnerability.

- **No Production Hardening:** This is a CTF challenge application, not a production system. Real-world applications would have WAF, rate limiting, HSTS, CSP, etc. These missing defenses are noted but not authorization vulnerabilities per se.

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**End of Authorization Analysis Report**