Spring Boot Security Review

Use when adding auth, handling input, creating endpoints, or dealing with secrets.

When to Activate

• Adding authentication (JWT, OAuth2, session-based)
• Implementing authorization (@PreAuthorize, role-based access)
• Validating user input (Bean Validation, custom validators)
• Configuring CORS, CSRF, or security headers
• Managing secrets (Vault, environment variables)
• Adding rate limiting or brute-force protection
• Scanning dependencies for CVEs

Authentication

• Prefer stateless JWT or opaque tokens with revocation list
• Use httpOnly, Secure, SameSite=Strict cookies for sessions
• Validate tokens with OncePerRequestFilter or resource server

@Component
public class JwtAuthFilter extends OncePerRequestFilter {
  private final JwtService jwtService;

  public JwtAuthFilter(JwtService jwtService) {
    this.jwtService = jwtService;
  }

  @Override
  protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response,
      FilterChain chain) throws ServletException, IOException {
    String header = request.getHeader(HttpHeaders.AUTHORIZATION);
    if (header != null && header.startsWith("Bearer ")) {
      String token = header.substring(7);
      Authentication auth = jwtService.authenticate(token);
      SecurityContextHolder.getContext().setAuthentication(auth);
    }
    chain.doFilter(request, response);
  }
}

OAuth 2.1 Requirements

• Mandate PKCE for all authorization code flows
• Prohibit Implicit Grant (removed in OAuth 2.1)
• Prohibit Resource Owner Password Credentials (ROPC)
• Implement Refresh Token Rotation: issue new refresh token on each use; invalidate old one
• Access token lifetime: 15 minutes maximum

JWT Validation

Always validate:

• alg claim: explicitly reject none algorithm
• exp: token must not be expired
• iss: must match expected issuer
• aud: must match expected audience

NimbusJwtDecoder decoder = NimbusJwtDecoder.withPublicKey(publicKey).build();
decoder.setJwtValidator(JwtValidators.createDefaultWithIssuer("https://auth.example.com"));
// The default validator checks exp, nbf, iss
// Explicitly configure audience validator:
OAuth2TokenValidator<Jwt> audienceValidator = new JwtClaimValidator<List<String>>(
    AUD, aud -> aud.contains("my-api"));

Authorization

• Enable method security: @EnableMethodSecurity
• Use @PreAuthorize("hasRole('ADMIN')") or @PreAuthorize("@authz.canEdit(#id)")
• Deny by default; expose only required scopes

@RestController
@RequestMapping("/api/admin")
public class AdminController {

  @PreAuthorize("hasRole('ADMIN')")
  @GetMapping("/users")
  public List<UserDto> listUsers() {
    return userService.findAll();
  }

  @PreAuthorize("@authz.isOwner(#id, authentication)")
  @DeleteMapping("/users/{id}")
  public ResponseEntity<Void> deleteUser(@PathVariable Long id) {
    userService.delete(id);
    return ResponseEntity.noContent().build();
  }
}

Input Validation

• Use Bean Validation with @Valid on controllers
• Apply constraints on DTOs: @NotBlank, @Email, @Size, custom validators
• Sanitize any HTML with a whitelist before rendering

// BAD: No validation
@PostMapping("/users")
public User createUser(@RequestBody UserDto dto) {
  return userService.create(dto);
}

// GOOD: Validated DTO
public record CreateUserDto(
    @NotBlank @Size(max = 100) String name,
    @NotBlank @Email String email,
    @NotNull @Min(0) @Max(150) Integer age
) {}

@PostMapping("/users")
public ResponseEntity<UserDto> createUser(@Valid @RequestBody CreateUserDto dto) {
  return ResponseEntity.status(HttpStatus.CREATED)
      .body(userService.create(dto));
}

SQL Injection Prevention

• Use Spring Data repositories or parameterized queries
• For native queries, use :param bindings; never concatenate strings

// BAD: String concatenation in native query
@Query(value = "SELECT * FROM users WHERE name = '" + name + "'", nativeQuery = true)

// GOOD: Parameterized native query
@Query(value = "SELECT * FROM users WHERE name = :name", nativeQuery = true)
List<User> findByName(@Param("name") String name);

// GOOD: Spring Data derived query (auto-parameterized)
List<User> findByEmailAndActiveTrue(String email);

Password Hashing

• Primary (recommended): Argon2id: new Argon2PasswordEncoder(16, 32, 1, 65536, 3) (Spring Security 5.8+)
• Acceptable fallback: BCrypt with work factor >= 12: new BCryptPasswordEncoder(12)
• Prohibited: MD5, SHA-*, unsalted hashes, PBKDF2 with < 100,000 iterations

@Bean
public PasswordEncoder passwordEncoder() {
    // Argon2id: saltLength=16, hashLength=32, parallelism=1, memory=65536, iterations=3
    return new Argon2PasswordEncoder(16, 32, 1, 65536, 3);
}

// In service
public User register(CreateUserDto dto) {
  String hashedPassword = passwordEncoder.encode(dto.password());
  return userRepository.save(new User(dto.email(), hashedPassword));
}

CSRF Protection

• For browser session apps, keep CSRF enabled; include token in forms/headers
• For pure APIs with Bearer tokens, disable CSRF and rely on stateless auth
• Document the reason whenever disabling CSRF

// Disable CSRF only for stateless APIs (JWT-authenticated, no session cookies).
// Document the reason here.
http.csrf(csrf -> csrf.disable()); // Stateless JWT API — no CSRF risk
http.sessionManagement(sm -> sm.sessionCreationPolicy(SessionCreationPolicy.STATELESS));

Secrets Management

• No secrets in source; load from env or vault
• Keep application.yml free of credentials; use placeholders
• Rotate tokens and DB credentials regularly

# BAD: Hardcoded in application.yml
spring:
  datasource:
    password: mySecretPassword123

# GOOD: Environment variable placeholder
spring:
  datasource:
    password: ${DB_PASSWORD}

# GOOD: Spring Cloud Vault integration
spring:
  cloud:
    vault:
      uri: https://vault.example.com
      token: ${VAULT_TOKEN}

Security Headers

No unsafe-inline or unsafe-eval in CSP. Use nonces for inline scripts/styles if absolutely necessary.

http.headers(headers -> headers
    .contentSecurityPolicy(csp ->
        csp.policyDirectives("default-src 'self'; script-src 'self' 'nonce-{random}'; style-src 'self' 'nonce-{random}'; img-src 'self' data:; frame-ancestors 'none'"))
    .frameOptions(HeadersConfigurer.FrameOptionsConfig::deny)
    .xssProtection(Customizer.withDefaults())
    .httpStrictTransportSecurity(hsts -> hsts
        .maxAgeInSeconds(63072000)
        .includeSubDomains(true)
        .preload(true))
    .referrerPolicy(referrer -> referrer
        .policy(ReferrerPolicyHeaderWriter.ReferrerPolicy.STRICT_ORIGIN_WHEN_CROSS_ORIGIN))
    .permissionsPolicy(permissions -> permissions
        .policy("camera=(), microphone=(), geolocation=()")));

Service-to-Service: mTLS

For internal service communication, enforce mutual TLS:

server:
  ssl:
    client-auth: need
    key-store: classpath:service.p12
    trust-store: classpath:trusted-cas.p12

CORS Configuration

• Configure CORS at the security filter level, not per-controller
• Restrict allowed origins: never use * in production

@Bean
public CorsConfigurationSource corsConfigurationSource() {
  CorsConfiguration config = new CorsConfiguration();
  config.setAllowedOrigins(List.of("https://app.example.com"));
  config.setAllowedMethods(List.of("GET", "POST", "PUT", "DELETE"));
  config.setAllowedHeaders(List.of("Authorization", "Content-Type"));
  config.setAllowCredentials(true);
  config.setMaxAge(3600L);

  UrlBasedCorsConfigurationSource source = new UrlBasedCorsConfigurationSource();
  source.registerCorsConfiguration("/api/**", config);
  return source;
}

// In SecurityFilterChain:
http.cors(cors -> cors.configurationSource(corsConfigurationSource()));

Rate Limiting

• Apply Bucket4j or gateway-level limits on expensive endpoints
• Log and alert on bursts; return 429 with retry hints

// Using Bucket4j for per-endpoint rate limiting
@Component
public class RateLimitFilter extends OncePerRequestFilter {
  private final Map<String, Bucket> buckets = new ConcurrentHashMap<>();

  private Bucket createBucket() {
    return Bucket.builder()
        .addLimit(Bandwidth.classic(100, Refill.intervally(100, Duration.ofMinutes(1))))
        .build();
  }

  @Override
  protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response,
      FilterChain chain) throws ServletException, IOException {
    String clientIp = request.getRemoteAddr();
    Bucket bucket = buckets.computeIfAbsent(clientIp, k -> createBucket());

    if (bucket.tryConsume(1)) {
      chain.doFilter(request, response);
    } else {
      response.setStatus(HttpStatus.TOO_MANY_REQUESTS.value());
      response.getWriter().write("{\"error\": \"Rate limit exceeded\"}");
    }
  }
}

Dependency Security

• Run OWASP Dependency Check / Snyk in CI
• Keep Spring Boot and Spring Security on supported versions
• Fail builds on known CVEs

Logging and PII

• Never log secrets, tokens, passwords, or full PAN data
• Redact sensitive fields; use structured JSON logging

File Uploads

• Validate size, content type, and extension
• Store outside web root; scan if required

Checklist Before Release

• [ ] Auth tokens validated and expired correctly
• [ ] Authorization guards on every sensitive path
• [ ] All inputs validated and sanitized
• [ ] No string-concatenated SQL
• [ ] CSRF posture correct for app type (documented if disabled)
• [ ] Secrets externalized; none committed
• [ ] Security headers configured (CSP without unsafe-inline/unsafe-eval, HSTS, Permissions-Policy)
• [ ] Rate limiting on APIs
• [ ] Dependencies scanned and up to date
• [ ] Logs free of sensitive data
• [ ] OAuth 2.1 flows use PKCE; no Implicit Grant or ROPC
• [ ] JWT validates alg (rejects none), exp, iss, aud
• [ ] Password hashing uses Argon2id or BCrypt (work factor >= 12)

Remember: Deny by default, validate inputs, least privilege, and secure-by-configuration first.