Nestjs Security

NestJS Security Audit

Audit NestJS applications. NestJS sits on top of Express or Fastify; specific patterns (decorators, DI, modules) introduce their own audit surface.

When this skill applies

• Reviewing Guards and authorization logic
• Auditing ValidationPipe configuration
• Reviewing Interceptors for unsafe transformations
• Checking module structure and provider scoping
• Reviewing GraphQL or REST controllers built on Nest

Workflow

Follow ../_shared/audit-workflow.md. Companion: nodejs-express-security for underlying middleware concerns.

Phase 1: Stack detection

grep -E '"@nestjs/(core|common|platform-express|platform-fastify)":' package.json
find . -name 'main.ts' -path '*src*' -not -path '*/node_modules/*'
find . -name 'nest-cli.json'

Detect: platform (Express vs Fastify), use of GraphQL (@nestjs/graphql), use of microservices (@nestjs/microservices).

Phase 2: Inventory

# Controllers and routes
grep -rn '@Controller\|@Get\|@Post\|@Put\|@Delete' src/ | head -50

# Guards
grep -rn '@UseGuards\|implements CanActivate' src/

# Interceptors
grep -rn '@UseInterceptors\|implements NestInterceptor' src/

# Pipes
grep -rn 'useGlobalPipes\|@UsePipes\|ValidationPipe' src/

# CORS
grep -rn 'enableCors\|cors:' src/main.ts src/app.module.ts 2>/dev/null

# Microservices
grep -rn 'createMicroservice\|@MessagePattern\|@EventPattern' src/

Phase 3: Detection — the checks

Guards

Guards implement CanActivate. They run before route handlers.

• NST-GUARD-1 Every endpoint that should be authenticated has @UseGuards(AuthGuard) or global app-level guard.
• NST-GUARD-2 Public endpoints explicitly marked (e.g., @Public() decorator), and the global guard checks for that decorator. Don't rely on "remembering" to apply guards.

  // GOOD pattern — global guard + opt-out
  app.useGlobalGuards(new AuthGuard(reflector));
  
  // controllers/auth.controller.ts
  @Public()
  @Post('login')
  login(@Body() dto: LoginDto) { ... }
  

• NST-GUARD-3 Role-based guards check the user's role against required roles via decorator metadata:

  @Roles('admin')
  @UseGuards(RolesGuard)
  

  Verify RolesGuard actually reads Roles metadata and compares.
• NST-GUARD-4 Guards don't short-circuit silently — return false or throw; never resolve to true on unexpected input.
• NST-GUARD-5 Per-resource authz (ownership checks) NOT done in guards (guards don't have easy access to mutated body); done in service layer.

ValidationPipe

• NST-PIPE-1 app.useGlobalPipes(new ValidationPipe({ whitelist: true, forbidNonWhitelisted: true, transform: true })) applied globally.
  • whitelist: true — strips properties not declared on the DTO. Prevents mass assignment.
  • forbidNonWhitelisted: true — REJECTS requests with extra properties (stricter).
  • transform: true — converts payload to DTO class instance, applying transforms.
• NST-PIPE-2 DTOs use class-validator decorators (@IsString, @IsEmail, @Length, etc.).
• NST-PIPE-3 Sensitive fields not exposed via @Expose() from class-transformer on response DTOs (use @Exclude() for password hashes etc., or use serializer interceptor).
• NST-PIPE-4 Nested DTOs use @Type(() => Nested) for transform to work recursively.

// dto/create-user.dto.ts
import { IsEmail, IsString, Length, IsOptional } from 'class-validator';

export class CreateUserDto {
  @IsEmail()
  email!: string;
  
  @IsString()
  @Length(8, 128)
  password!: string;
  
  @IsString()
  @Length(1, 50)
  displayName!: string;
  
  // role is intentionally not on the DTO — set by server
}

Interceptors

• NST-INT-1 Logging interceptors don't log full request body (password, secrets).
• NST-INT-2 Serialization interceptor strips sensitive response fields:

  @UseInterceptors(ClassSerializerInterceptor)
  

  Combined with @Exclude() on the entity, ensures secrets don't ship.
• NST-INT-3 Caching interceptors keyed by user/tenant when caching per-user data (otherwise cross-user cache hits).

Exception filters

• NST-EX-1 Global exception filter in production hides stack traces and internal error details.
• NST-EX-2 Specific HTTP exceptions (UnauthorizedException, ForbiddenException, NotFoundException) used appropriately — don't return 500 for client errors.
• NST-EX-3 Database error details (constraint names, table names) not bubbled to clients.

Middleware

NestJS supports both Express middleware and Nest-style middleware. Order matters:

• NST-MW-1 Security middleware (helmet, cors) configured in main.ts before app.listen().
• NST-MW-2 Rate limiting via @nestjs/throttler or express-rate-limit. Throttler applied globally or per-controller.
• NST-MW-3 app.enableCors(...) with specific options (not enableCors() with default *).

Modules and DI scoping

• NST-DI-1 Request-scoped providers used for per-request state (e.g., logger with request ID). Don't put per-request data in singleton-scoped providers.
• NST-DI-2 Sensitive services (e.g., AuthService) only exported from modules that should access them; don't exports: [AuthService] from auth module to public modules without need.
• NST-DI-3 @Global() modules limited to truly global concerns.

Authentication strategies (Passport)

If using @nestjs/passport:

• NST-AUTH-1 JWT strategy validates signature, expiry, issuer, audience. See saas-security-pack/saas-code-security-review/references/jwt-validation.md.
• NST-AUTH-2 Local strategy compares password with bcrypt.compare (constant-time); don't use ===.
• NST-AUTH-3 Session-based: connect session middleware before Passport.
• NST-AUTH-4 Refresh token rotation implemented (issue new RT on use, revoke old).

GraphQL (if using @nestjs/graphql)

• NST-GQL-1 Apollo Driver config: introspection disabled in production, playground disabled.
• NST-GQL-2 Resolvers use @UseGuards(...) for auth.
• NST-GQL-3 See graphql-security skill for depth/complexity, field-level auth.

Microservices (TCP, Redis, Kafka, gRPC transports)

• NST-MS-1 Microservice transport not exposed publicly. TCP transport with default settings binds to all interfaces.
• NST-MS-2 Message handlers (@MessagePattern) validate inputs — they're effectively RPC endpoints without HTTP middleware.
• NST-MS-3 Inter-service auth: signed messages or mTLS between services; don't rely on network-only isolation.

File uploads

• NST-UP-1 @nestjs/platform-express Multer config has size and count limits.
• NST-UP-2 Validate file type by magic bytes (see nodejs-express-security).

Config module

• NST-CFG-1 ConfigModule with validate function ensures required env vars present at startup.
• NST-CFG-2 Secrets accessed via ConfigService.get('SECRET') — not from process.env directly (so test/runtime config swapping works).
• NST-CFG-3 validationSchema (Joi or Zod) requires specific env shape; fails fast on misconfiguration.

Dependencies

• NST-DEP-1 NestJS versions current (10.x or 11.x).
• NST-DEP-2 Companion: nodejs-express-security for underlying Express/Fastify checks.

Phase 4: Triage

Critical: missing global ValidationPipe with whitelist; sensitive route without @UseGuards; CORS open with credentials; microservice handlers with no input validation.

Phase 5: Report

Use ../_shared/findings-schema.md. Prefix IDs with NST-.