Fix Improper Error Handling in Spring WebFlux
Improper error handling in Spring WebFlux is a goldmine for reconnaissance. By default, unhandled exceptions in a reactive stream can leak stack traces, internal class names, and sensitive database metadata. In a non-blocking environment, failing to explicitly catch and sanitize error signals allows the underlying framework to dump raw diagnostic data directly into the HTTP response body.
The Vulnerable Pattern
@GetMapping("/user/lookup")
public Mono lookupUser(@RequestParam String id) {
return userRepository.findById(id)
.switchIfEmpty(Mono.error(new RuntimeException("Database connection failed for ID: " + id)))
.map(user -> {
if (user.isRestricted()) throw new IllegalStateException("Internal Logic Error: Access Denied for " + user.getEmail());
return user;
});
} The Secure Implementation
The vulnerable snippet allows raw exception messages (including sensitive emails and internal logic states) to reach the client because it lacks a global error handling strategy. The secure implementation utilizes @RestControllerAdvice to intercept all signals in the WebFlux pipeline. It logs the full stack trace internally for the SOC/Dev teams while returning an opaque, sanitized JSON object to the requester. This prevents 'Information Exposure through Error Messages' (CWE-209) and breaks the attacker's feedback loop during exploitation.
@RestControllerAdvice public class SecurityExceptionHandler {private static final Logger logger = LoggerFactory.getLogger(SecurityExceptionHandler.class); @ExceptionHandler(Exception.class) public Mono<ResponseEntity<Map<String, String>>> handleGenericError(Exception ex) { // Log the actual telemetry for internal debugging logger.error("Internal Error Intercepted: ", ex); // Return a sanitized, opaque response to the client Map<String, String> errorBody = Map.of( "status", "500", "error", "Internal Server Error", "message", "An unexpected error occurred. Reference ID: " + UUID.randomUUID() ); return Mono.just(ResponseEntity.status(HttpStatus.INTERNAL_SERVER_ERROR).body(errorBody)); }
}
Your Spring WebFlux API
might be exposed to Improper Error Handling
74% of Spring WebFlux apps fail this check. Hackers use automated scanners to find this specific flaw. Check your codebase before they do.
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