diff --git a/app.py b/app.py
index f85eed1..8ed7cc9 100644
--- a/app.py
+++ b/app.py
@@ -1,6 +1,7 @@
 from flask import Flask, render_template, request, jsonify, redirect, url_for, send_file, session
-import sqlite3, os, uuid
+import sqlite3, os, uuid, time
 from datetime import datetime, date
+from urllib.parse import urlparse
 from werkzeug.utils import secure_filename
 from auth import (login_user, logout_user, current_user, is_logged_in,
                   is_superadmin, is_admin, login_required, admin_required,
@@ -8,7 +9,28 @@ from auth import (login_user, logout_user, current_user, is_logged_in,
                   create_initial_superadmin)
 
 app = Flask(__name__)
-app.secret_key = 'marine_maint_secret_2026_xK9p'
+
+# ── Security: SECRET_KEY desde variable de entorno ───────────────────────────
+_secret_key = os.environ.get('SECRET_KEY')
+if not _secret_key:
+    _secret_key = 'marine_maint_secret_2026_xK9p'
+    print('⚠️  WARNING: SECRET_KEY no configurado en variables de entorno. '
+          'Crea un archivo .env con SECRET_KEY=<clave aleatoria> antes de producción.')
+app.secret_key = _secret_key
+
+# ── Rate-limiting simple para login (sin dependencias externas) ──────────────
+_login_attempts: dict = {}   # ip -> [timestamps]
+_LOGIN_MAX    = 10
+_LOGIN_WINDOW = 900          # 15 minutos
+
+def _is_rate_limited(ip: str) -> bool:
+    now = time.time()
+    attempts = [t for t in _login_attempts.get(ip, []) if now - t < _LOGIN_WINDOW]
+    _login_attempts[ip] = attempts
+    return len(attempts) >= _LOGIN_MAX
+
+def _record_failed_login(ip: str):
+    _login_attempts.setdefault(ip, []).append(time.time())
 
 BASE_DIR     = os.path.dirname(os.path.abspath(__file__))
 DB_PATH      = os.path.join(BASE_DIR, 'marine_maintenance.db')
@@ -268,6 +290,10 @@ def auth_login():
     error = None
     username = ''
     if request.method == 'POST':
+        ip = request.remote_addr or '0.0.0.0'
+        if _is_rate_limited(ip):
+            error = 'Demasiados intentos fallidos. Espera 15 minutos.'
+            return render_template('login.html', error=error, username='')
         username = request.form.get('username','').strip()
         password = request.form.get('password','')
         conn = get_db()
@@ -279,7 +305,13 @@ def auth_login():
         conn.close()
         if user and verify_password(password, user['password_hash']):
             login_user(user)
-            return redirect(request.args.get('next') or url_for('dashboard'))
+            # Validar next para prevenir open redirect
+            next_url = request.args.get('next') or url_for('dashboard')
+            parsed = urlparse(next_url)
+            if parsed.netloc and parsed.netloc != request.host:
+                next_url = url_for('dashboard')
+            return redirect(next_url)
+        _record_failed_login(ip)
         error = 'Usuario o contraseña incorrectos.'
     return render_template('login.html', error=error, username=username)
 
@@ -814,13 +846,32 @@ def work_order_detail(woid):
                            vessel_owner_email=conn2_data.get('owner_email',''),
                            vessel_owner_name=conn2_data.get('owner_name',''))
 
+_VALID_WO_STATUSES = {'pending', 'in_progress', 'completed', 'cancelled', 'on_hold'}
+
+def _check_wo_access(conn, woid):
+    """Verifica que el WO pertenece a la empresa del usuario actual."""
+    company_id = cid()
+    if company_id is None:   # superadmin ve todo
+        return True
+    row = conn.execute("""
+        SELECT wo.id FROM work_orders wo
+        JOIN vessels v ON wo.vessel_id = v.id
+        WHERE wo.id=? AND v.company_id=?
+    """, (woid, company_id)).fetchone()
+    return row is not None
+
 @app.route('/work-orders/<int:woid>/update-status', methods=['POST'])
 @login_required
 def update_status(woid):
     status = request.json.get('status')
+    if status not in _VALID_WO_STATUSES:
+        return jsonify({'error': 'Estado inválido'}), 400
     conn = get_db()
-    extra = ", end_date=date('now')" if status=='completed' else ""
-    conn.execute(f"UPDATE work_orders SET status=?,updated_at=CURRENT_TIMESTAMP{extra} WHERE id=?", (status,woid))
+    if not _check_wo_access(conn, woid):
+        conn.close()
+        return jsonify({'error': 'No autorizado'}), 403
+    extra = ", end_date=date('now')" if status == 'completed' else ""
+    conn.execute(f"UPDATE work_orders SET status=?,updated_at=CURRENT_TIMESTAMP{extra} WHERE id=?", (status, woid))
     conn.commit(); conn.close()
     # Auto-save PDF when completed
     if status == 'completed':
@@ -874,6 +925,8 @@ def update_status(woid):
 def update_fields(woid):
     data = request.json
     conn = get_db()
+    if not _check_wo_access(conn, woid):
+        conn.close(); return jsonify({'error': 'No autorizado'}), 403
     conn.execute("""UPDATE work_orders SET root_cause=?,repairs_done=?,
         updated_at=CURRENT_TIMESTAMP WHERE id=?""",
         (data.get('root_cause',''),data.get('repairs_done',''),woid))
@@ -885,6 +938,8 @@ def update_fields(woid):
 def update_labor(woid):
     data = request.json
     conn = get_db()
+    if not _check_wo_access(conn, woid):
+        conn.close(); return jsonify({'error': 'No autorizado'}), 403
     conn.execute("""UPDATE work_orders SET labor_hours=?, labor_rate=?,
         updated_at=CURRENT_TIMESTAMP WHERE id=?""",
         (float(data.get('labor_hours', 0)),
@@ -896,6 +951,10 @@ def update_labor(woid):
 @login_required
 def upload_photo(woid):
     if 'photo' not in request.files: return jsonify({'error':'No file'}),400
+    conn_chk = get_db()
+    if not _check_wo_access(conn_chk, woid):
+        conn_chk.close(); return jsonify({'error': 'No autorizado'}), 403
+    conn_chk.close()
     f = request.files['photo']
     if f and allowed_file(f.filename, ALLOWED_IMG):
         ext = f.filename.rsplit('.',1)[1].lower()
@@ -916,6 +975,8 @@ def add_part_to_order(woid):
     qty = float(data.get('quantity',1))
     cost = float(data.get('unit_cost',0))
     conn = get_db()
+    if not _check_wo_access(conn, woid):
+        conn.close(); return jsonify({'error': 'No autorizado'}), 403
     conn.execute("INSERT INTO work_order_parts (work_order_id,part_id,description,quantity,unit_cost) VALUES (?,?,?,?,?)",
                  (woid,part_id or None,data.get('description',''),qty,cost))
     if part_id:
@@ -1164,6 +1225,8 @@ def purchase_detail(pid):
 def purchase_update_status(pid):
     data = request.json
     new_status = data.get('status')
+    if new_status not in PURCHASE_STATUSES:
+        return jsonify({'error': 'Estado inválido'}), 400
     conn = get_db()
     extra_fields = ""
     extra_vals = []
@@ -1200,6 +1263,8 @@ def upload_invoice(pid):
     f = request.files.get('invoice')
     if not f or not f.filename:
         return jsonify({'ok': False, 'error': 'No file'})
+    if not allowed_file(f.filename, ALLOWED_DOCS):
+        return jsonify({'ok': False, 'error': 'Tipo de archivo no permitido'})
     ext = f.filename.rsplit('.',1)[-1].lower()
     fname = f"invoice_{pid}_{datetime.now().strftime('%Y%m%d_%H%M%S')}.{ext}"
     f.save(os.path.join(UPLOAD_FOLDER, fname))
@@ -1494,6 +1559,8 @@ def api_wo_equipment(woid):
     return jsonify([dict(i) for i in items])
 
 # ── SIGNATURES ───────────────────────────────────────────────────────────────
+_SIG_COLS = {'tech': 'signature_tech', 'client': 'signature_client'}
+
 @app.route('/work-orders/<int:woid>/save-signature', methods=['POST'])
 @login_required
 def save_signature(woid):
@@ -1503,6 +1570,10 @@ def save_signature(woid):
     dataurl = data.get('dataUrl', '')
     if not who or not dataurl:
         return jsonify({'error': 'Missing data'}), 400
+    # Allowlist: solo 'tech' o 'client' son válidos
+    col = _SIG_COLS.get(who)
+    if not col:
+        return jsonify({'error': 'Parámetro who inválido'}), 400
     # Strip header: data:image/png;base64,....
     match = re.match(r'data:image/\w+;base64,(.*)', dataurl, re.DOTALL)
     if not match:
@@ -1511,9 +1582,10 @@ def save_signature(woid):
     fname = f"sig_{woid}_{who}_{uuid.uuid4().hex[:6]}.png"
     with open(os.path.join(SIG_FOLDER, fname), 'wb') as f:
         f.write(img_bytes)
-    col = 'signature_tech' if who == 'tech' else 'signature_client'
     conn = get_db()
-    # Delete old file if exists
+    if not _check_wo_access(conn, woid):
+        conn.close(); return jsonify({'error': 'No autorizado'}), 403
+    # Delete old file if exists (col ya está validado contra allowlist)
     old = conn.execute(f"SELECT {col} FROM work_orders WHERE id=?", (woid,)).fetchone()
     if old and old[col]:
         op = os.path.join(SIG_FOLDER, old[col])
@@ -1526,8 +1598,12 @@ def save_signature(woid):
 @login_required
 def clear_signature(woid):
     who = request.json.get('who')
-    col = 'signature_tech' if who == 'tech' else 'signature_client'
+    col = _SIG_COLS.get(who)
+    if not col:
+        return jsonify({'error': 'Parámetro who inválido'}), 400
     conn = get_db()
+    if not _check_wo_access(conn, woid):
+        conn.close(); return jsonify({'error': 'No autorizado'}), 403
     old = conn.execute(f"SELECT {col} FROM work_orders WHERE id=?", (woid,)).fetchone()
     if old and old[col]:
         fp = os.path.join(SIG_FOLDER, old[col])
diff --git a/auth.py b/auth.py
index 67b7bdf..d03c75a 100644
--- a/auth.py
+++ b/auth.py
@@ -112,7 +112,13 @@ def verify_password(password, hashed):
     return check_password_hash(hashed, password)
 
 # ── Crear superadmin inicial ──────────────────────────────────────────────────
-def create_initial_superadmin(username='admin', password='admin123', email='admin@marine.local'):
+def create_initial_superadmin(username='admin', password=None, email='admin@marine.local'):
+    """Crea el superadmin solo si no existe ninguno.
+    Password: variable de entorno ADMIN_PASSWORD, o 'admin123' como último recurso.
+    """
+    import os
+    if password is None:
+        password = os.environ.get('ADMIN_PASSWORD', 'admin123')
     conn = get_db()
     existing = conn.execute("SELECT id FROM users WHERE role='superadmin'").fetchone()
     if not existing:
@@ -121,5 +127,9 @@ def create_initial_superadmin(username='admin', password='admin123', email='admi
             VALUES (NULL, ?, ?, ?, 'Super Administrator', 'superadmin')
         """, (username, email, hash_password(password)))
         conn.commit()
-        print(f"[AUTH] Superadmin creado: {username} / {password}")
+        if password == 'admin123':
+            print(f"[AUTH] ⚠️  Superadmin creado con contraseña por defecto. "
+                  f"Configura ADMIN_PASSWORD en tu .env y reinicia.")
+        else:
+            print(f"[AUTH] Superadmin creado: {username}")
     conn.close()