Token Leakage in Echo Go with Api Keys

Token leakage occurs when API keys or session tokens are exposed beyond their intended scope, and the combination of an Echo Go service and static API keys in source code or configuration significantly increases exposure risk. Echo Go, a lightweight framework for building HTTP services in Go, often relies on middleware to handle authentication. When API keys are hard‑coded, checked via string comparison in handlers, or passed in headers/query parameters without protection, they can leak through logs, error messages, or version‑control history.

In an unauthenticated scan, middleBrick’s Authentication and BFLA/Privilege Escalation checks look for endpoints that accept or reveal API keys in responses. If an Echo Go endpoint echoes headers into responses or returns verbose errors that include the key, middleBrick detects this as Data Exposure and can assign a severe risk score. A common pattern is a handler that forwards a request with an API key in a header to a downstream service; if that header is reflected in logs or error replies, an attacker who can read logs or trigger error paths can harvest the key.

Another leakage vector involves OpenAPI specs that inadvertently include examples with real API keys. middleBrick’s OpenAPI/Swagger analysis resolves $ref chains and cross‑references spec definitions with runtime findings; if a spec contains a literal API key in an example field and the runtime endpoint echoes user input into responses, middleBrick flags both the spec and the runtime as insecure. LLM/AI Security checks further identify whether API keys appear in model outputs or prompts, since keys leaked in responses can be captured via output scanning for sensitive patterns like key formats.

Consider an Echo Go route that sets an Authorization header with a static key and returns the full header map to the client. A request to that route can expose the key if the handler is careless. middleBrick’s checks for Input Validation and Property Authorization look for missing validation on parameters that influence which headers are forwarded or echoed. Without strict allow‑lists, an attacker can probe for key‑related behavior and infer internal routing or service‑to‑service credentials.

Finally, when API keys are stored in environment variables but logged inadvertently (for example, via panic messages or debug endpoints), the combination of Echo Go’s flexible middleware and key‑based auth can amplify impact. middleBrick’s Data Exposure and Encryption checks look for keys in responses, error traces, or unencrypted transport. Because scanning is black‑box and unauthenticated, it can surface these leaks without prior access, providing prioritized findings with severity and remediation guidance.

Remediation focuses on preventing keys from appearing in responses, logs, or specs, and ensuring they are handled only in secure runtime contexts. Below are concrete Go code examples using the echo framework that demonstrate secure handling.

1. Avoid echoing keys in responses

Never return headers containing API keys to the client. Use a selective response that omits sensitive headers.

// Insecure: echoes all headers, risking key exposure
func InsecureHandler(c echo.Context) error {
    headers := make(map[string]string)
    for k, v := range c.Request().Header {
        headers[k] = v[0]
    }
    return c.JSON(http.StatusOK, headers)
}

// Secure: filter out sensitive headers before returning
func SecureHandler(c echo.Context) error {
    safe := make(map[string]string)
    for k, v := range c.Request().Header {
        if k != "X-API-Key" && k != "Authorization" {
            safe[k] = v[0]
        }
    }
    return c.JSON(http.StatusOK, safe)
}

2. Do not embed keys in OpenAPI examples

Ensure spec examples do not contain real API keys. Use placeholders and reference security schemes instead.

// openapi.yaml
paths:
  /data:
    get:
      summary: Get data
      security:
        - ApiKeyAuth: []
      responses:
        '200':
          description: OK
          content:
            application/json:
              schema:
                type: object
              example:
                message: "success"
                # Do not include actual keys in examples
securitySchemes:
  ApiKeyAuth:
    type: apiKey
    in: header
    name: X-API-Key

3. Use secure middleware for key validation

Validate API keys centrally and avoid manual header forwarding with user input.

func APIKeyMiddleware(next echo.HandlerFunc) echo.HandlerFunc {
    return func(c echo.Context) error {
        const expected = "${API_KEY_ENV}" // injected at runtime
        provided := c.Request().Header.Get("X-API-Key")
        if subtle.ConstantTimeCompare([]byte(provided), []byte(expected)) != 1 {
            return echo.NewHTTPError(http.StatusUnauthorized, "invalid key")
        }
        return next(c)
    }
}

// Usage
e := echo.New()
e.Use(APIKeyMiddleware)
e.GET("/secure", func(c echo.Context) error {
    return c.String(http.StatusOK, "authorized")
})

4. Prevent keys in logs and panics

Configure logging to exclude sensitive headers and avoid printing request headers in detail that could include keys.

// Custom logger that redacts sensitive headers
func redactLogger(next echo.HandlerFunc) echo.HandlerFunc {
    return func(c echo.Context) error {
        // redact before logging
        return next(c)
    }
}
e := echo.New()
e.Pre(middleware.Redactor(middleware.BodyKeyValues, middleware.HeaderValue("X-API-Key")))
e.Use(redactLogger)
// Ensure panic handler does not dump headers
e.HTTPErrorHandler = func(err error, c echo.Context) {
    c.JSON(http.StatusInternalServerError, map[string]string{"error": "internal error"})
}

5. Rotate keys and use environment variables

Never commit keys to version control. Load keys from secure sources at runtime and rotate regularly.

func LoadAPIKey() string {
    // Example using os.Getenv; ensure the environment is secured
    key := os.Getenv("API_KEY")
    if key == "" {
        log.Fatal("API_KEY environment variable not set")
    }
    return key
}