Security First Validator

Security-First Validator

Enforces security requirements for all Django REST Framework API endpoints.

Activation Triggers

This skill activates when:

• Creating API views or viewsets
• Creating serializers
• Mentioning "endpoint", "API", "view", "route"
• Writing DRF classes (APIView, ViewSet, Serializer)
• Creating URL patterns for APIs
• Discussing authentication or permissions

Security Requirements (MANDATORY)

Every API endpoint MUST have:

1. Permission Classes (REQUIRED)

from rest_framework import viewsets
from rest_framework.permissions import IsAuthenticated

class UserViewSet(viewsets.ModelViewSet):
    permission_classes = [IsAuthenticated]  # ✅ REQUIRED
    # ...

2. Serializer Validation (REQUIRED)

from rest_framework import serializers

class UserSerializer(serializers.ModelSerializer):
    class Meta:
        model = User
        fields = ['id', 'email', 'first_name']
        # NO sensitive fields exposed ✅

    def validate_email(self, value):
        # Custom validation ✅
        if not value.endswith('@company.com'):
            raise serializers.ValidationError("Must use company email")
        return value

3. No Raw SQL (REQUIRED)

# ❌ DANGEROUS
User.objects.raw(f"SELECT * FROM users WHERE id = {user_id}")

# ✅ SAFE
User.objects.filter(id=user_id)

4. Rate Limiting (REQUIRED for sensitive endpoints)

from rest_framework.throttling import UserRateThrottle

class LoginView(APIView):
    throttle_classes = [UserRateThrottle]  # ✅ REQUIRED for auth
    # ...

Validation Process

Step 1: Detect New API Endpoint

When API code is being written:

class UserViewSet(viewsets.ModelViewSet):
    queryset = User.objects.all()
    serializer_class = UserSerializer
    # Missing security! ❌

Step 2: Run Security Checklist

Verify:

1. ✅ Permission classes defined
2. ✅ Serializer has proper validation
3. ✅ No raw SQL queries
4. ✅ Rate limiting on sensitive endpoints
5. ✅ No password/token fields in serializer
6. ✅ Proper CORS configuration

Step 3: Auto-Add Security Requirements

Before (Insecure):

class UserViewSet(viewsets.ModelViewSet):
    queryset = User.objects.all()
    serializer_class = UserSerializer

After (Secure):

from rest_framework import viewsets
from rest_framework.permissions import IsAuthenticated

class UserViewSet(viewsets.ModelViewSet):
    """User management endpoints."""

    queryset = User.objects.all()
    serializer_class = UserSerializer
    permission_classes = [IsAuthenticated]  # ✅ Added

    def get_queryset(self):
        """Filter queryset to exclude soft-deleted records."""
        return super().get_queryset().filter(is_deleted=False)

Step 4: Validate Serializer Security

Check for exposed sensitive fields:

# ❌ DANGEROUS - Exposes password!
class UserSerializer(serializers.ModelSerializer):
    class Meta:
        model = User
        fields = '__all__'  # Never use __all__!

Auto-fix to:

# ✅ SAFE - Explicit field list
class UserSerializer(serializers.ModelSerializer):
    class Meta:
        model = User
        fields = ['id', 'email', 'first_name', 'last_name']
        read_only_fields = ['id', 'created_at', 'updated_at']
        # Password excluded ✅

Step 5: Report Security Issues

Report to developer:

Security Issues Detected and Fixed

Fixed:

1. ✅ Added permission_classes = [IsAuthenticated] to UserViewSet
2. ✅ Changed serializer from fields = '__all__' to explicit field list
3. ✅ Excluded sensitive fields (password, tokens)
4. ✅ Added read_only_fields for audit fields

Why:

• Permission classes prevent unauthorized access
• Explicit fields prevent accidental data exposure
• Read-only fields prevent tampering with audit trail

Complete Secure Endpoint Example

import users.models as _users_models
import users.serializers as _users_serializers

from rest_framework import viewsets, status
from rest_framework.decorators import action
from rest_framework.permissions import IsAuthenticated
from rest_framework.response import Response
from rest_framework.throttling import UserRateThrottle


class UserViewSet(viewsets.ModelViewSet):
    """
    User management API.

    Security:
    - Requires authentication
    - Users can only access their own data (see get_queryset)
    - Rate limited for sensitive actions
    - Input validation via serializer
    """

    queryset = _users_models.User.objects.all()
    serializer_class = _users_serializers.UserSerializer
    permission_classes = [IsAuthenticated]  # ✅ Authentication required

    def get_queryset(self):
        """Users can only see active, non-deleted records."""
        qs = super().get_queryset().filter(is_deleted=False)

        # Users see only their own data unless admin
        if not self.request.user.is_staff:
            qs = qs.filter(id=self.request.user.id)

        return qs

    def perform_create(self, serializer):
        """Auto-set created_by on creation."""
        serializer.save(created_by=self.request.user)

    @action(
        detail=False,
        methods=['post'],
        throttle_classes=[UserRateThrottle],  # ✅ Rate limiting
        permission_classes=[IsAuthenticated]
    )
    def change_password(self, request):
        """Change user password (rate limited)."""
        serializer = _serializers.ChangePasswordSerializer(data=request.data)
        serializer.is_valid(raise_exception=True)  # ✅ Validation

        user = request.user
        user.set_password(serializer.validated_data['new_password'])
        user.save()

        return Response({'status': 'password changed'})

Security Checklist by Endpoint Type

Read-Only Endpoints (GET)

class PublicArticleViewSet(viewsets.ReadOnlyModelViewSet):
    """Public articles (read-only)."""

    queryset = Article.objects.filter(is_published=True, is_deleted=False)
    serializer_class = ArticleSerializer
    permission_classes = [AllowAny]  # ✅ Explicit - public endpoint

    # Still apply rate limiting to prevent scraping
    throttle_classes = [AnonRateThrottle]

Create Endpoints (POST)

class UserCreateView(generics.CreateAPIView):
    """User registration (public)."""

    serializer_class = UserCreateSerializer
    permission_classes = [AllowAny]  # ✅ Public registration
    throttle_classes = [AnonRateThrottle]  # ✅ Prevent abuse

    def perform_create(self, serializer):
        """
        Create user and send verification email.

        Security: Rate limited, email validation in serializer.
        """
        user = serializer.save()
        send_verification_email(user)

Update Endpoints (PUT/PATCH)

class UserUpdateView(generics.UpdateAPIView):
    """Update user profile."""

    serializer_class = UserUpdateSerializer
    permission_classes = [IsAuthenticated, IsOwner]  # ✅ Auth + ownership

    def get_object(self):
        """Users can only update their own profile."""
        return self.request.user

Delete Endpoints (DELETE)

class UserDestroyView(generics.DestroyAPIView):
    """Soft delete user account."""

    permission_classes = [IsAuthenticated, IsOwner]  # ✅ Auth + ownership

    def perform_destroy(self, instance):
        """Soft delete instead of hard delete."""
        instance.is_deleted = True
        instance.save(update_fields=['is_deleted', 'updated_at'])

Common Security Violations

Violation 1: No Permission Classes

# ❌ DANGEROUS - Anyone can access!
class AdminViewSet(viewsets.ModelViewSet):
    queryset = User.objects.all()

Auto-fix:

# ✅ SECURE
class AdminViewSet(viewsets.ModelViewSet):
    queryset = User.objects.all()
    permission_classes = [IsAuthenticated, IsAdminUser]  # Added!

Violation 2: Serializer Exposes Sensitive Data

# ❌ DANGEROUS - Exposes password!
class UserSerializer(serializers.ModelSerializer):
    class Meta:
        model = User
        fields = '__all__'

I auto-fix:

# ✅ SECURE
class UserSerializer(serializers.ModelSerializer):
    class Meta:
        model = User
        fields = ['id', 'email', 'first_name', 'last_name', 'created_at']
        read_only_fields = ['id', 'created_at', 'updated_at']
        # password, tokens excluded!

Violation 3: Raw SQL Injection Risk

# ❌ DANGEROUS - SQL injection!
def get_user(user_id):
    query = f"SELECT * FROM users WHERE id = {user_id}"
    return User.objects.raw(query)

I auto-fix:

# ✅ SECURE
def get_user(user_id):
    return User.objects.filter(id=user_id).first()

Violation 4: No Rate Limiting on Auth

# ❌ DANGEROUS - Brute force attacks possible!
class LoginView(APIView):
    def post(self, request):
        # Login logic
        pass

I auto-fix:

# ✅ SECURE
from rest_framework.throttling import AnonRateThrottle

class LoginView(APIView):
    throttle_classes = [AnonRateThrottle]  # Added!

    def post(self, request):
        # Login logic
        pass

OWASP Top 10 Coverage

Automatically check for:

1. Broken Access Control → Permission classes required
2. Cryptographic Failures → No sensitive fields in serializers
3. Injection → No raw SQL, use ORM
4. Insecure Design → Enforce secure-by-default patterns
5. Security Misconfiguration → CORS, HTTPS, rate limiting
6. Vulnerable Components → (Check in CI/CD)
7. Authentication Failures → Throttling on auth endpoints
8. Data Integrity Failures → Serializer validation required
9. Logging Failures → (Suggest logging for sensitive ops)
10. SSRF → Validate URLs in serializers

Custom Permission Classes

Recognize and allow custom permissions:

from rest_framework.permissions import BasePermission

class IsOwner(BasePermission):
    """User can only access their own objects."""

    def has_object_permission(self, request, view, obj):
        return obj.user == request.user


# Usage ✅ VALID
class ProfileViewSet(viewsets.ModelViewSet):
    permission_classes = [IsAuthenticated, IsOwner]

Integration with Other Skills

Works together with:

• model-entity-validator: Ensures models don't expose sensitive fields
• test-coverage-advisor: Suggests security tests
• django-reviewer: Full security audit during review

Success Criteria

✅ ALL endpoints have permission classes ✅ ALL serializers use explicit field lists ✅ NO raw SQL queries ✅ Rate limiting on sensitive endpoints ✅ NO sensitive fields exposed ✅ Input validation on all write operations ✅ Developer understands OWASP risks

Behavior

Proactive enforcement:

• Check security without being asked
• Add permission classes automatically
• Fix serializer field exposure immediately
• Explain WHY each security measure is critical
• Reference OWASP categories

Never:

• Require explicit "check security" request
• Wait for pen test results
• Just warn without fixing
• Allow endpoints without security

Block completion if:

• No permission classes defined
• Serializer uses fields = '__all__'
• Raw SQL detected
• Sensitive endpoints lack rate limiting