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GuardAPI
Automated Security Protocol

How to fix Improper Error Handling
in Vapor (Swift)

Executive Summary

Improper error handling in Vapor applications is a primary source of information disclosure. Defaulting to raw error propagation leaks database schemas, internal file paths, and stack traces, providing an attacker with the exact blueprint needed for exploitation. To secure a Vapor API, you must decouple internal failure details from the HTTP response body.

The Vulnerable Pattern

VULNERABLE CODE
app.get("user", ":id") { req -> EventLoopFuture in
    let id = req.parameters.get("id")!
    return User.find(id, on: req.db)
        .unwrap(or: Abort(.internalServerError, reason: "Database query failed for user \(id)")) // LEAK: Exposes internal logic/ID
}

app.post(“upload”) { req throws -> String in
let data = try req.content.decode(FileData.self) // LEAK: Raw Swift errors thrown here can expose property names and validation logic
return “Success”
}

The Secure Implementation

The vulnerable code directly injects dynamic data or raw error descriptions into the 'reason' field of an Abort object, which Vapor serializes to the client. The secure implementation utilizes a custom Middleware to intercept all errors. It checks the HTTP status code: if it's a 500 (Internal Server Error), it replaces the specific error message with a generic 'An internal error occurred' string. Detailed error context is sent to the system logger, ensuring developers have the data needed for forensics without handing a roadmap to an external adversary.

SECURE CODE
struct SanitizeErrorMiddleware: Middleware {
    func respond(to request: Request, chainingTo next: Responder) -> EventLoopFuture {
        return next.respond(to: request).flatMapError { error in
            let status: HTTPResponseStatus = (error as? AbortError)?.status ?? .internalServerError
            let reason = (status == .internalServerError) ? "An internal error occurred." : (error as? AbortError)?.reason ?? "Unknown error"

        // Log the actual detailed error internally for debugging
        request.logger.error("Caught Error: \(error.localizedDescription) - Full Info: \(error)")
        
        let response = Response(status: status)
        try? response.content.encode(["error": true, "message": reason], as: .json)
        return request.eventLoop.makeSucceededFuture(response)
    }
}


}


// Register in configure.swift
app.middleware.use(SanitizeErrorMiddleware())

System Alert • ID: 3619
Target: Vapor (Swift) API
Potential Vulnerability

Your Vapor (Swift) API might be exposed to Improper Error Handling

74% of Vapor (Swift) apps fail this check. Hackers use automated scanners to find this specific flaw. Check your codebase before they do.

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