Api Key Exposure in Echo Go with Mssql

When building HTTP services in Go using the Echo framework and interacting with Microsoft SQL Server via the database/sql driver with a MSSQL driver (such as github.com/denisenkom/go-mssqldb), developers often embed connection strings that contain API keys or secrets. If route handlers inadvertently expose these keys through logs, error messages, or debug endpoints, the combination of Echo, Go, and MSSQL becomes a vector for credential leakage.

For example, consider a handler that opens a MSSQL connection using a connection string constructed from environment variables, but then returns the full string or a parsed credential in a JSON response:

package main

import (
	"database/sql"
	"fmt"
	"net/http"
	"os"

	"github.com/labstack/echo/v4"
	_ "github.com/denisenkom/go-mssqldb"
)

func debugHandler(c echo.Context) error {
	server := os.Getenv("MSSQL_SERVER")
	port := os.Getenv("MSSQL_PORT")
	user := os.Getenv("MSSQL_USER")
	password := os.Getenv("MSSQL_PASSWORD")
	database := os.Getenv("MSSQL_DATABASE")

	connString := fmt.Sprintf("server=%s;port=%s;user id=%s;password=%s;database=%s;", server, port, user, password, database)

	// Dangerous: returning the connection string can expose API keys/secrets
	return c.JSON(http.StatusOK, map[string]string{
		"connection_string": connString,
	})
}

func main() {
	e := echo.New()
	e.GET("/debug", debugHandler)
	e.Start(":8080")
}

If this handler is reachable without authentication (for instance, because route-level middleware is missing or misconfigured), an attacker can obtain the MSSQL connection string, which often contains an API key or password. In MSSQL, the connection string may also include access token parameters used for Azure authentication, effectively exposing an API key. Because Echo routes are easy to map and Go binaries often retain source structure in debug endpoints, this misconfiguration is frequently discoverable via automated scans. The risk is compounded when the same binary is used across environments (dev/staging/prod), making a single leaked key broadly impactful.

Additionally, improper error handling in Go MSSQL code can leak sensitive data. For instance, returning detailed SQL errors to the client may expose query structure or internal paths that aid an attacker in crafting further attacks:

func getUser(c echo.Context) error {
	ctx := context.Background()
	server := os.Getenv("MSSQL_SERVER")
	port := os.Getenv("MSSQL_PORT")
	user := os.Getenv("MSSQL_USER")
	password := os.Getenv("MSSQL_PASSWORD")
	database := os.Getenv("MSSQL_DATABASE")

	connString := fmt.Sprintf("server=%s;port=%s;user id=%s;password=%s;database=%s;", server, port, user, password, database)
	db, err := sql.Open("sqlserver", connString)
	if err != nil {
		// Dangerous: exposing internal error details
		return c.String(http.StatusInternalServerError, err.Error())
	}
	defer db.Close()

	var id int
	if err := db.QueryRowContext(ctx, "SELECT id FROM users WHERE username = @p1", c.Param("username")).Scan(&id); err != nil {
		return c.String(http.StatusInternalServerError, err.Error())
	}
	return c.JSON(http.StatusOK, map[string]int{"user_id": id})
}

In this scenario, a verbose MSSQL error could reveal the database name, table structure, or even hint at the presence of an API key used in the connection string. Because middleBrick scans the unauthenticated attack surface and tests input validation and data exposure, such misconfigurations would be flagged with high severity, linking the Echo route to the MSSQL backend exposure.

To prevent API key exposure when using Echo and MSSQL in Go, apply the following secure coding practices. First, never construct or return connection strings to clients. Instead, keep sensitive values server-side and use parameterized queries to avoid injection and accidental leakage.

Secure handler example that avoids exposing MSSQL credentials:

package main

import (
	"context"
	"database/sql"
	"net/http"

	"github.com/labstack/echo/v4"
	_ "github.com/denisenkom/go-mssqldb"
)

func getUser(c echo.Context) error {
	ctx := context.Background()
	server := "localhost"
	port := 1433
	user := "app_user"
	password := "SuperSecretPassword123" // ideally sourced securely at runtime
	database := "appdb"

	connString := fmt.Sprintf("server=%s;port=%d;user id=%s;password=%s;database=%s;", server, port, user, password, database)
	db, err := sql.Open("sqlserver", connString)
	if err != nil {
		// Log the error internally; return a generic message to the client
		return c.String(http.StatusInternalServerError, "internal server error")
	}
	defer db.Close()

	var id int
	if err := db.QueryRowContext(ctx, "SELECT id FROM users WHERE username = @p1", c.Param("username")).Scan(&id); err != nil {
		if err == sql.ErrNoRows {
			return c.JSON(http.StatusNotFound, map[string]string{"error": "user not found"})
		}
		return c.String(http.StatusInternalServerError, "internal server error")
	}
	return c.JSON(http.StatusOK, map[string]int{"user_id": id})
}

Key remediation steps:

• Do not expose connection_string or any credential-containing variable in HTTP responses.
• Use parameterized queries (e.g., @p1) to prevent injection and avoid string concatenation that might expose values in error messages.
• Return generic error messages to clients and log detailed errors internally for monitoring.
• Ensure that any API key stored in MSSQL (e_call it an access token) is never serialized or returned by API endpoints.

When using the middleBrick CLI (middlebrick scan <url>) or GitHub Action, these fixes help ensure that the scan does not flag authentication bypass, data exposure, or input validation findings related to MSSQL-backed services. The dashboard can track improvements over time, and the Pro plan’s continuous monitoring can alert you if a regression introduces a route that echoes sensitive configuration.