diff --git a/backend/app/Controllers/AuthController.php b/backend/app/Controllers/AuthController.php
index d69a3ef..c59e759 100644
--- a/backend/app/Controllers/AuthController.php
+++ b/backend/app/Controllers/AuthController.php
@@ -39,13 +39,13 @@ class AuthController extends BaseController
         try {
             // Create Company
             $companyId = Company::create([
-                'name' => htmlspecialchars(strip_tags($data['company_name']))
+                'name' => $data['company_name']
             ]);
 
             // Create Admin User for this Company
             $userId = User::createSecure([
                 'company_id' => $companyId,
-                'name'       => htmlspecialchars(strip_tags($data['user_name'])),
+                'name'       => $data['user_name'],
                 'email'      => strtolower(trim($data['email'])),
                 'password'   => $data['password'],
                 'role'       => 'admin'
@@ -127,7 +127,7 @@ class AuthController extends BaseController
     {
         $user = User::find($request->user_id);
         
-        if (!$user) {
+        if (!$user || (int)$user['company_id'] !== (int)$request->company_id) {
             $response->json(['error' => 'User not found'], 404);
             return;
         }
diff --git a/backend/app/Core/Request.php b/backend/app/Core/Request.php
index 5f4a54e..a04d998 100644
--- a/backend/app/Core/Request.php
+++ b/backend/app/Core/Request.php
@@ -13,6 +13,11 @@ class Request
     private array $bodyParams;
     private array $headers;
 
+    // Explicit properties to store authentication details to avoid deprecation warnings in PHP 8.2+
+    public ?int $user_id = null;
+    public ?int $company_id = null;
+    public ?string $role = null;
+
     public function __construct()
     {
         $this->method = strtoupper($_SERVER['REQUEST_METHOD'] ?? 'GET');
diff --git a/backend/app/Core/Response.php b/backend/app/Core/Response.php
index ddeac34..af6c41d 100644
--- a/backend/app/Core/Response.php
+++ b/backend/app/Core/Response.php
@@ -39,10 +39,12 @@ class Response
         $this->setStatusCode($code);
         $this->setHeader('Content-Type', 'application/json; charset=utf-8');
         
-        // Setup base CORS headers for our API
-        $this->setHeader('Access-Control-Allow-Origin', '*');
+        // Setup CORS headers — restrict origin to the configured allowed domain
+        $allowedOrigin = getenv('ALLOWED_ORIGIN') ?: '*';
+        $this->setHeader('Access-Control-Allow-Origin', $allowedOrigin);
         $this->setHeader('Access-Control-Allow-Methods', 'GET, POST, PUT, DELETE, OPTIONS');
         $this->setHeader('Access-Control-Allow-Headers', 'Content-Type, Authorization, X-Requested-With');
+        $this->setHeader('Vary', 'Origin'); // Required when Access-Control-Allow-Origin is not *
 
         $this->sendHeaders();
         http_response_code($this->statusCode);
diff --git a/backend/app/Core/Router.php b/backend/app/Core/Router.php
index 400e182..62e1188 100644
--- a/backend/app/Core/Router.php
+++ b/backend/app/Core/Router.php
@@ -75,9 +75,11 @@ class Router
 
         // Handle CORS Preflight Preemptively
         if ($method === 'OPTIONS') {
-            $response->setHeader('Access-Control-Allow-Origin', '*');
+            $allowedOrigin = getenv('ALLOWED_ORIGIN') ?: '*';
+            $response->setHeader('Access-Control-Allow-Origin', $allowedOrigin);
             $response->setHeader('Access-Control-Allow-Methods', 'GET, POST, PUT, DELETE, OPTIONS');
             $response->setHeader('Access-Control-Allow-Headers', 'Content-Type, Authorization, X-Requested-With');
+            $response->setHeader('Vary', 'Origin');
             $response->setStatusCode(200);
             exit;
         }
@@ -116,12 +118,14 @@ class Router
                     return;
                 }
 
-                $response->error("Handler error for route: {$path}", 500);
+                error_log("Handler error for route: [{$method}] {$path}");
+                $response->error("Internal Server Error", 500);
                 return;
             }
         }
 
         // Route not found
-        $response->error("Route not found: [{$method}] {$path}", 404);
+        error_log("Route not found: [{$method}] {$path}");
+        $response->error("Not Found", 404);
     }
 }
diff --git a/backend/app/Core/Security.php b/backend/app/Core/Security.php
index 7d42521..0cffaa2 100644
--- a/backend/app/Core/Security.php
+++ b/backend/app/Core/Security.php
@@ -14,7 +14,10 @@ class Security
      */
     private static function getEncryptionKey(): string
     {
-        $key = getenv('ENCRYPTION_KEY') ;
+        $key = getenv('ENCRYPTION_KEY');
+        if (!$key || strlen($key) < 16) {
+            throw new \RuntimeException("ENCRYPTION_KEY environment variable is empty or too short. Cryptographic operations aborted.");
+        }
         return substr(hash('sha256', $key, true), 0, 32);
     }
 
@@ -23,7 +26,11 @@ class Security
      */
     private static function getHmacSalt(): string
     {
-        return getenv('HMAC_SALT');
+        $salt = getenv('HMAC_SALT');
+        if (!$salt) {
+            throw new \RuntimeException("HMAC_SALT environment variable is empty. Cryptographic operations aborted.");
+        }
+        return $salt;
     }
 
     /**
@@ -31,7 +38,11 @@ class Security
      */
     private static function getJwtSecret(): string
     {
-        return getenv('JWT_SECRET');
+        $secret = getenv('JWT_SECRET');
+        if (!$secret) {
+            throw new \RuntimeException("JWT_SECRET environment variable is empty. Cryptographic operations aborted.");
+        }
+        return $secret;
     }
 
     /**
diff --git a/backend/app/Middlewares/RateLimitMiddleware.php b/backend/app/Middlewares/RateLimitMiddleware.php
new file mode 100644
index 0000000..521cdb4
--- /dev/null
+++ b/backend/app/Middlewares/RateLimitMiddleware.php
@@ -0,0 +1,94 @@
+<?php
+
+namespace App\Middlewares;
+
+use App\Core\Request;
+use App\Core\Response;
+
+/**
+ * Rate Limit Middleware
+ * Limits the number of requests per IP address using file-based counters.
+ * Protects sensitive endpoints (login, register) from Brute Force attacks.
+ */
+class RateLimitMiddleware
+{
+    /**
+     * Maximum allowed requests within the time window
+     */
+    private int $maxAttempts;
+
+    /**
+     * Time window in seconds
+     */
+    private int $decaySeconds;
+
+    public function __construct(int $maxAttempts = 5, int $decaySeconds = 60)
+    {
+        $this->maxAttempts  = $maxAttempts;
+        $this->decaySeconds = $decaySeconds;
+    }
+
+    public function handle(Request $request, Response $response): void
+    {
+        $ip  = $this->getClientIp();
+        $key = 'rate_' . md5($ip . '_' . $request->getPath());
+
+        $storageDir = APP_ROOT . '/storage/rate_limits';
+        if (!is_dir($storageDir)) {
+            mkdir($storageDir, 0750, true);
+        }
+
+        $filePath = $storageDir . '/' . $key . '.json';
+
+        $data = ['count' => 0, 'expires_at' => time() + $this->decaySeconds];
+
+        if (file_exists($filePath)) {
+            $raw = json_decode(file_get_contents($filePath), true);
+            if ($raw && isset($raw['expires_at']) && $raw['expires_at'] > time()) {
+                // Window still active — use existing data
+                $data = $raw;
+            }
+            // If window expired, fall through and reset (overwrite with fresh data below)
+        }
+
+        $data['count']++;
+
+        if ($data['count'] > $this->maxAttempts) {
+            $retryAfter = max(0, $data['expires_at'] - time());
+            $response->setHeader('Retry-After', (string)$retryAfter);
+            $response->json([
+                'error'   => 'Too Many Requests',
+                'message' => "You have exceeded the maximum number of {$this->maxAttempts} attempts. Please try again in {$retryAfter} seconds."
+            ], 429);
+            return;
+        }
+
+        // Persist the updated counter
+        file_put_contents($filePath, json_encode($data), LOCK_EX);
+    }
+
+    /**
+     * Get real client IP, accounting for proxies
+     */
+    private function getClientIp(): string
+    {
+        $headers = [
+            'HTTP_CF_CONNECTING_IP',   // Cloudflare
+            'HTTP_X_FORWARDED_FOR',
+            'HTTP_X_REAL_IP',
+            'REMOTE_ADDR'
+        ];
+
+        foreach ($headers as $header) {
+            if (!empty($_SERVER[$header])) {
+                // X-Forwarded-For can be a comma-separated list; take first
+                $ip = trim(explode(',', $_SERVER[$header])[0]);
+                if (filter_var($ip, FILTER_VALIDATE_IP)) {
+                    return $ip;
+                }
+            }
+        }
+
+        return '0.0.0.0';
+    }
+}
diff --git a/backend/app/Middlewares/SecurityMiddleware.php b/backend/app/Middlewares/SecurityMiddleware.php
index 251e30d..978daa6 100644
--- a/backend/app/Middlewares/SecurityMiddleware.php
+++ b/backend/app/Middlewares/SecurityMiddleware.php
@@ -33,7 +33,7 @@ class SecurityMiddleware
     }
 
     /**
-     * Recursively sanitize input arrays
+     * Recursively trim input arrays
      */
     private function sanitizeArray(array $data): array
     {
@@ -42,8 +42,7 @@ class SecurityMiddleware
             if (is_array($value)) {
                 $sanitized[$key] = $this->sanitizeArray($value);
             } elseif (is_string($value)) {
-                // Strip HTML tags and convert special characters to HTML entities
-                $sanitized[$key] = htmlspecialchars(strip_tags(trim($value)), ENT_QUOTES, 'UTF-8');
+                $sanitized[$key] = trim($value);
             } else {
                 $sanitized[$key] = $value;
             }
diff --git a/backend/app/Models/BaseModel.php b/backend/app/Models/BaseModel.php
index 8f65cb7..bcbdb03 100644
--- a/backend/app/Models/BaseModel.php
+++ b/backend/app/Models/BaseModel.php
@@ -12,12 +12,42 @@ abstract class BaseModel
     protected static string $table = '';
     protected static string $primaryKey = 'id';
 
+    /**
+     * Validate table, primary key, and column names to prevent SQL injection.
+     */
+    protected static function getSafeTable(): string
+    {
+        $table = static::$table;
+        if (!preg_match('/^[a-zA-Z0-9_]+$/', $table)) {
+            throw new \InvalidArgumentException("Invalid table name: {$table}");
+        }
+        return $table;
+    }
+
+    protected static function getSafePrimaryKey(): string
+    {
+        $primaryKey = static::$primaryKey;
+        if (!preg_match('/^[a-zA-Z0-9_]+$/', $primaryKey)) {
+            throw new \InvalidArgumentException("Invalid primary key: {$primaryKey}");
+        }
+        return $primaryKey;
+    }
+
+    protected static function validateColumns(array $columns): void
+    {
+        foreach ($columns as $column) {
+            if (!preg_match('/^[a-zA-Z0-9_]+$/', $column)) {
+                throw new \InvalidArgumentException("Invalid column name: {$column}");
+            }
+        }
+    }
+
     /**
      * Retrieve all records
      */
     public static function all(): array
     {
-        $table = static::$table;
+        $table = static::getSafeTable();
         return Database::select("SELECT * FROM {$table}");
     }
 
@@ -29,22 +59,27 @@ abstract class BaseModel
      */
     public static function find($id): ?array
     {
-        $table = static::$table;
-        $primaryKey = static::$primaryKey;
+        // Enforce integer conversion or validate to prevent type misuse
+        $id = is_numeric($id) ? (int)$id : $id;
+        $table = static::getSafeTable();
+        $primaryKey = static::getSafePrimaryKey();
         return Database::selectOne("SELECT * FROM {$table} WHERE {$primaryKey} = :id LIMIT 1", ['id' => $id]);
     }
 
     /**
      * Insert a new record
      *
-     * @param array $data Assocation array of columns and values
+     * @param array $data Association array of columns and values
      * @return string Last inserted primary key ID
      */
     public static function create(array $data): string
     {
-        $table = static::$table;
-        $columns = implode(', ', array_keys($data));
-        $placeholders = ':' . implode(', :', array_keys($data));
+        $table = static::getSafeTable();
+        $columnKeys = array_keys($data);
+        static::validateColumns($columnKeys);
+
+        $columns = implode(', ', $columnKeys);
+        $placeholders = ':' . implode(', :', $columnKeys);
 
         $sql = "INSERT INTO {$table} ({$columns}) VALUES ({$placeholders})";
         return Database::insert($sql, $data);
@@ -59,11 +94,15 @@ abstract class BaseModel
      */
     public static function update($id, array $data): int
     {
-        $table = static::$table;
-        $primaryKey = static::$primaryKey;
+        $id = is_numeric($id) ? (int)$id : $id;
+        $table = static::getSafeTable();
+        $primaryKey = static::getSafePrimaryKey();
+        
+        $columnKeys = array_keys($data);
+        static::validateColumns($columnKeys);
 
         $sets = [];
-        foreach (array_keys($data) as $column) {
+        foreach ($columnKeys as $column) {
             $sets[] = "{$column} = :{$column}";
         }
         $setSql = implode(', ', $sets);
@@ -81,8 +120,9 @@ abstract class BaseModel
      */
     public static function delete($id): int
     {
-        $table = static::$table;
-        $primaryKey = static::$primaryKey;
+        $id = is_numeric($id) ? (int)$id : $id;
+        $table = static::getSafeTable();
+        $primaryKey = static::getSafePrimaryKey();
 
         $sql = "DELETE FROM {$table} WHERE {$primaryKey} = :id";
         return Database::execute($sql, ['id' => $id]);
diff --git a/backend/app/bootstrap.php b/backend/app/bootstrap.php
index d3797f7..d47d669 100644
--- a/backend/app/bootstrap.php
+++ b/backend/app/bootstrap.php
@@ -55,3 +55,32 @@ if ($isDebug) {
     ini_set('display_errors', '0');
     error_reporting(0);
 }
+
+// 4. Global Uncaught Exception Handler
+// Catches any unhandled exception anywhere in the app and returns a clean JSON error
+// instead of leaking PHP stack traces to the browser.
+set_exception_handler(function (\Throwable $e) {
+    $isDebug = filter_var(getenv('APP_DEBUG') ?: true, FILTER_VALIDATE_BOOLEAN);
+
+    error_log('[EXCEPTION] ' . get_class($e) . ': ' . $e->getMessage() . ' in ' . $e->getFile() . ':' . $e->getLine());
+
+    if (!headers_sent()) {
+        header('Content-Type: application/json; charset=utf-8');
+        http_response_code(500);
+    }
+
+    $body = ['error' => 'Internal Server Error'];
+
+    // In debug mode, expose details to the developer only
+    if ($isDebug) {
+        $body['debug'] = [
+            'exception' => get_class($e),
+            'message'   => $e->getMessage(),
+            'file'      => $e->getFile(),
+            'line'      => $e->getLine(),
+        ];
+    }
+
+    echo json_encode($body, JSON_UNESCAPED_UNICODE | JSON_PRETTY_PRINT);
+    exit(1);
+});
diff --git a/backend/public/index.php b/backend/public/index.php
index f496c9f..a259813 100644
--- a/backend/public/index.php
+++ b/backend/public/index.php
@@ -20,23 +20,20 @@ $router = new Router();
 $router->use(\App\Middlewares\SecurityMiddleware::class);
 
 // 4. Define API Routes
+// Health Check — no php_version or environment in production to avoid info disclosure
 $router->get('/api/health', function ($request, $response) {
     $response->json([
-        'status' => 'success',
-        'message' => 'Nabeh API is healthy',
-        'details' => [
-            'app_name' => getenv('APP_NAME') ?: 'Nabeh',
-            'environment' => getenv('APP_ENV') ?: 'development',
-            'php_version' => PHP_VERSION,
-            'time' => date('Y-m-d H:i:s')
-        ]
+        'status'   => 'success',
+        'message'  => 'Nabeh API is healthy',
+        'app_name' => getenv('APP_NAME') ?: 'Nabeh',
+        'time'     => date('Y-m-d H:i:s')
     ]);
 });
 
-// Authentication Routes
-$router->post('/api/auth/register', [\App\Controllers\AuthController::class, 'register']);
-$router->post('/api/auth/login', [\App\Controllers\AuthController::class, 'login']);
-$router->get('/api/auth/me', [\App\Controllers\AuthController::class, 'me'], [\App\Middlewares\AuthMiddleware::class]);
+// Authentication Routes (Rate-limited: 5 attempts per 60 seconds per IP)
+$router->post('/api/auth/register', [\App\Controllers\AuthController::class, 'register'], [\App\Middlewares\RateLimitMiddleware::class]);
+$router->post('/api/auth/login',    [\App\Controllers\AuthController::class, 'login'],    [\App\Middlewares\RateLimitMiddleware::class]);
+$router->get('/api/auth/me',        [\App\Controllers\AuthController::class, 'me'],       [\App\Middlewares\AuthMiddleware::class]);
 
 
 // 4. Dispatch the request
diff --git a/implementation_plan.md b/implementation_plan.md
index 6f530c6..c1f6bc9 100644
--- a/implementation_plan.md
+++ b/implementation_plan.md
@@ -251,4 +251,48 @@ server {
 > - هل ترغب بإنشاء مسار `POST /api/auth/register` مفتوح للجميع لإنشاء حسابات شركات جديدة؟ أم نكتفي حالياً بإنشاء مستخدم مدير (Admin) افتراضي يدوياً أو عبر سكربت ليكون النظام مغلقاً للشركات المعتمدة فقط؟
 > - في عملية تسجيل الدخول، هل نحتاج لإرجاع بيانات الشركة المرتبطة بالمستخدم ضمن نفس الـ Response، أم نكتفي بإرجاع التوكن (Token) وبيانات المستخدم الأساسية فقط؟
 
+---
+
+## المرحلة الخامسة: معالجة وإصلاح الثغرات الأمنية (Security Audit Remediation)
+
+بناءً على التقرير الأمني الصادر، سنقوم بتطبيق التعديلات البرمجية لرفع مستوى أمان الخادم وحماية البيانات.
+
+### Proposed Changes
+
+#### [MODIFY] [Security.php](file:///Users/hamzaaleghwairyeen/development/App/nabeh/backend/app/Core/Security.php)
+- إرجاع خطأ (Exception) فوراً في حال عدم وجود متغيرات البيئة (`ENCRYPTION_KEY`, `HMAC_SALT`, `JWT_SECRET`) لمنع تشفير البيانات بمفاتيح فارغة.
+
+#### [MODIFY] [BaseModel.php](file:///Users/hamzaaleghwairyeen/development/App/nabeh/backend/app/Models/BaseModel.php)
+- تنظيف وفلترة أسماء الأعمدة ديناميكياً باستخدام مصفوفة بيضاء (Whitelist Regex) لمنع ثغرات الـ SQL Injection عبر أسماء الأعمدة في دالتي `create()` و `update()`.
+
+#### [MODIFY] [SecurityMiddleware.php](file:///Users/hamzaaleghwairyeen/development/App/nabeh/backend/app/Middlewares/SecurityMiddleware.php)
+- إلغاء تطبيق `htmlspecialchars` و `strip_tags` على المدخلات الخام القادمة للخلفية لمنع تلف كلمات المرور والرموز الخاصة، وتأجيل التنظيف ليكون حصراً عند الطباعة/العرض (Output Encoding).
+
+#### [MODIFY] [AuthController.php](file:///Users/hamzaaleghwairyeen/development/App/nabeh/backend/app/Controllers/AuthController.php)
+- إزالة التنظيف المزدوج (Double Encoding) لأسماء المستخدمين والشركات.
+
+#### [MODIFY] [Router.php](file:///Users/hamzaaleghwairyeen/development/App/nabeh/backend/app/Core/Router.php)
+- إخفاء مسار الملفات الحقيقي من رسائل الخطأ 404 و 500 وإظهار رسائل عامة لمنع تسريب بنية المجلدات (Information Disclosure).
+
+#### [MODIFY] [Response.php](file:///Users/hamzaaleghwairyeen/development/App/nabeh/backend/app/Core/Response.php)
+- جعل رابط الـ CORS ديناميكياً يعتمد على متغير بيئة `ALLOWED_ORIGIN` بدلاً من فتح النطاق للجميع عبر `*`.
+
+#### [MODIFY] [bootstrap.php](file:///Users/hamzaaleghwairyeen/development/App/nabeh/backend/app/bootstrap.php)
+- تسجيل معالج أخطاء عام (`set_exception_handler` / `set_error_handler`) لتحويل الأخطاء الفادحة غير المعالجة إلى استجابات JSON نظيفة ومخفية في الإنتاج، مع تسجيل التفاصيل التقنية في الـ `error_log` فقط.
+
+#### [MODIFY] [Request.php](file:///Users/hamzaaleghwairyeen/development/App/nabeh/backend/app/Core/Request.php)
+- تعريف الخصائص المعرفية (`$user_id`, `$company_id`, `$role`) بشكل صريح لتفادي مشاكل الخصائص الديناميكية (Dynamic Properties Deprecation) في إصدارات PHP 8.2+.
+
+#### [NEW] [RateLimitMiddleware.php](file:///Users/hamzaaleghwairyeen/development/App/nabeh/backend/app/Middlewares/RateLimitMiddleware.php)
+- بناء فلتر مخصص للحد من معدل الطلبات (Rate Limiting) على مسارات تسجيل الدخول والتسجيل لحماية التطبيق من محاولات التخمين العنيف (Brute Force).
+
+#### [MODIFY] [index.php](file:///Users/hamzaaleghwairyeen/development/App/nabeh/backend/public/index.php)
+- تفعيل فلتر الحد من معدل الطلبات على مسارات الحماية.
+
+### User Review Required
+
+> [!IMPORTANT]
+> هل نعتمد نظام تخزين المحاولات للحد من معدل الطلبات (Rate Limiting) في ملفات مؤقتة داخل مجلد `storage/` محلي (سهل الإعداد ومستقل)، أم نستخدم جدولاً مخصصاً في قاعدة البيانات؟
+
 </div>
+