Api Key Exposure in Fiber with Mysql

When building APIs with Fiber and a Mysql backend, developers often embed database credentials, service tokens, or internal connection strings directly in handler code or configuration files. If these files are committed to a repository or accidentally exposed through debug endpoints, an API key can be leaked. This exposure is particularly risky because Fiber routes may inadvertently return detailed errors or configuration details that reveal file paths, environment variables, or database identifiers tied to Mysql, giving an attacker context to craft follow-up attacks.

Consider a typical Fiber handler that opens a Mysql connection using a hardcoded DSN. In a black-box scan, middleBrick tests unauthenticated endpoints and examines responses for sensitive data patterns. If an endpoint returns stack traces containing Mysql error messages (e.g., access denied for user), or if there is an OpenAPI spec that documents query parameters without enforcing authentication, middleBrick can detect that an API key or database identity might be inferred from runtime behavior. The 12 security checks run in parallel, including Authentication, Input Validation, and Data Exposure, which together identify whether API keys or database connection artifacts appear in responses.

An unauthenticated LLM endpoint, if present, compounds the issue: system prompt leakage detection and active prompt injection testing from middleBrick’s LLM/AI Security checks can reveal whether prompts or results expose Mysql-related metadata. For example, a verbose error from a database query might include table names or column names that, when combined with a leaked API key in logs, enables privilege escalation or data exfiltration. middleBrick cross-references OpenAPI/Swagger specs (with full $ref resolution) against runtime findings, ensuring that any mismatch between declared authentication and observed data exposure is surfaced as a finding with severity and remediation guidance.

Using the CLI tool, you can run middlebrick scan <url> to obtain a per-category breakdown, including Data Exposure and Authentication, with prioritized findings and remediation steps. The Web Dashboard allows you to track scores over time, and the GitHub Action can fail builds if the risk score drops below your chosen threshold, helping prevent accidental commits of Mysql credentials. The MCP Server enables scanning directly from AI coding assistants, so that suggestions involving database connection code are checked before they are applied.

To reduce the chance of API key exposure when using Fiber with Mysql, store credentials outside source code and enforce strict error handling. Use environment variables injected at runtime and avoid returning raw database errors to clients. The following examples demonstrate secure patterns.

First, configure your Mysql connection using environment variables in main.go, and ensure errors are sanitized:

// main.go
package main

import (
	"database/sql"
	"log"
	"os"

	"github.com/gofiber/fiber/v2"
	_ "github.com/go-sql-driver/mysql"
)

func main() {
	dsn := os.Getenv("MYSQL_DSN") // e.g., user:password@tcp(127.0.0.1:3306)/dbname
	if dsn == "" {
		log.Fatal("MYSQL_DSN environment variable is required")
	}
	db, err := sql.Open("mysql", dsn)
	if err != nil {
		log.Fatal("failed to connect to mysql: ", err)
	}
	defer db.Close()

	app := fiber.New()
	app.Get("/users/:id", func(c *fiber.Ctx) error {
		var name string
		err := db.QueryRow("SELECT name FROM users WHERE id = ?", c.Params("id")).Scan(&name)
		if err != nil {
			if err == sql.ErrNoRows {
				return c.Status(fiber.StatusNotFound).JSON(fiber.Map{"error": "not found"})
			}
			// Do not expose Mysql error details
			return c.Status(fiber.StatusInternalServerError).JSON(fiber.Map{"error": "internal error"})
		}
		return c.JSON(fiber.Map{"name": name})
	})

	log.Fatal(app.Listen(":3000"))
}

Second, validate and sanitize all inputs to prevent injection and information leakage. Use prepared statements and avoid concatenating SQL strings. For dynamic queries, define strict allowlists for column and table names:

// handlers.go
func GetUser(c *fiber.Ctx, db *sql.DB) error {
	id := c.Params("id")
	// Basic validation to reduce unexpected behavior
	if id == "" {
		return c.Status(fiber.StatusBadRequest).JSON(fiber.Map{"error": "missing id"})
	}
	var name string
	row := db.QueryRow("SELECT name FROM users WHERE id = ? LIMIT 1", id)
	if err := row.Scan(&name); err != nil {
		if err == sql.ErrNoRows {
			return c.Status(fiber.StatusNotFound).JSON(fiber.Map{"error": "user not found"})
		}
		return c.Status(fiber.StatusInternalServerError).JSON(fiber.Map{"error": "internal error"})
	}
	return c.JSON(fiber.Map{"name": name})
}

Third, rotate keys regularly and restrict Mysql user permissions to the minimum required. Create a dedicated user with read-only access for queries that do not modify data, and use role-based access controls at the database level. These practices reduce the impact if an API key is exposed and complement middleBrick’s findings by lowering the severity of potential findings related to Data Exposure and Privilege Escalation.