Sandbox Escape in Echo Go with Api Keys

A sandbox escape in the context of an Echo Go service occurs when an attacker who has limited execution space (for example, through a server-side template injection or an insecure plugin loader) is able to break out and make arbitrary HTTP requests to the host environment or internal services. When API keys are used for authorization inside that service, the escape can expose those keys and allow the attacker to act with the permissions of the compromised component.

Echo Go applications often define routes and handlers that conditionally forward requests to backend APIs using keys stored in configuration or injected via environment variables. If input validation is weak, an attacker can craft a request that triggers an internal redirect or server-side request to an admin endpoint, causing the Echo Go runtime to include the API key in that outbound call. Because the key is trusted by the backend, the attacker can perform actions such as reading or modifying data, changing configurations, or invoking privileged operations that would normally be restricted to internal services.

Consider an endpoint that accepts a URL parameter to call a third-party service. Without strict allowlisting of hostnames and paths, an attacker can provide a value such as http://localhost:8080/admin/rotate that the Echo Go server resolves internally. The handler that adds the API key to the Authorization header will then send that key to the internal admin interface, effectively leaking it in the process. This pattern is commonly flagged by the BFLA/Privilege Escalation and Unsafe Consumption checks in middleBrick, which identify endpoints that can trigger internal requests with trusted credentials.

The LLM/AI Security checks in middleBrick further highlight risks when API keys are exposed through generated text, such as when an LLM integration logs or echoes keys in model responses. Output scanning for API keys ensures that keys are not inadvertently surfaced, while system prompt leakage detection helps prevent prompts that could cause the service to reveal key handling logic. Combined with a sandbox escape, these exposures can lead to rapid lateral movement within the deployment environment.

In architectural terms, sandbox escape in Echo Go with API keys is less about the language runtime and more about the composition of routes, middleware, and outbound HTTP clients. If authorization logic does not strictly validate targets before attaching credentials, an attacker can coerce the service into acting as a proxy. middleBrick’s Inventory Management and Property Authorization checks help surface these misconfigurations by comparing spec definitions with runtime behavior, ensuring that routes do not implicitly inherit overly broad permissions.

Remediation focuses on preventing the service from using API keys for untrusted destinations and ensuring keys are never reflected to clients. The following patterns demonstrate secure handling in Echo Go.

1. Validate and restrict outbound targets

Before making an HTTP request, verify the host and path against an allowlist. Do not construct URLs directly from user input.

package main

import (
    "net/http"
    "strings"

    "github.com/labstack/echo/v4"
)

var allowedHosts = map[string][]string{
    "api.example.com": {"/v1/resource"},
    "data.service.com": {"/query", "/status"},
}

func safeProxy(c echo.Context) error {
    target := c.QueryParam("target")
    if target == "" {
        return c.String(http.StatusBadRequest, "target is required")
    }

    // Basic parsing without making a request
    if !strings.HasPrefix(target, "https://") {
        return c.String(http.StatusBadRequest, "only HTTPS is allowed")
    }

    // Allowlist check
    var host, path string
    // simplistic split for example; use a proper URL parser in production
    parts := strings.SplitN(target[8:], "/", 2)
    host = parts[0]
    if len(parts) > 1 {
        path = "/" + parts[1]
    } else {
        path = "/"
    }

    allowedPaths, ok := allowedHosts[host]
    if !ok {
        return c.String(http.StatusForbidden, "host not allowed")
    }

    allowed := false
    for _, p := range allowedPaths {
        if path == p {
            allowed = true
            break
        }
    }
    if !allowed {
        return c.String(http.StatusForbidden, "path not allowed")
    }

    req, err := http.NewRequest(http.MethodGet, target, nil)
    if err != nil {
        return c.String(http.StatusInternalServerError, "invalid request")
    }

    // Inject key only for allowed destinations
    req.Header.Set("Authorization", "Bearer "+c.Get("apiKey").(string))

    resp, err := http.DefaultClient.Do(req)
    if err != nil {
        return c.String(http.StatusBadGateway, "upstream error")
    }
    defer resp.Body.Close()

    return c.Status(resp.StatusCode)
}

2. Avoid logging or echoing API keys

Ensure that keys are not included in request logs, error messages, or LLM outputs. Use structured logging that redacts sensitive headers.

package main

import (
    "github.com/labstack/echo/v4"
    "github.com/labstack/echo/v4/middleware"
)

func main() {
    e := echo.New()

    // Redact sensitive headers in logs
    e.Pre(middleware.Rederer())
    e.Use(middleware.RequestLoggerWithConfig(middleware.RequestLoggerConfig{
        LogValuesFunc: func(c echo.Context, v middleware.RequestLoggerValues) error {
            // Custom redaction logic here
            return nil
        },
    }))

    e.GET("/data", func(c echo.Context) error {
        apiKey := c.Get("apiKey")
        // Do not include apiKey in any response or log line
        return c.JSON(http.StatusOK, map[string]string{"status": "ok"})
    })

    e.Start(":8080")
}

3. Use scoped tokens instead of long-lived API keys

Where possible, use short-lived tokens with minimal scopes. The Echo Go handler should request a scoped token from a trusted vault at startup and refresh it as needed, rather than embedding a raw key in configuration that could be exposed through a sandbox escape.

// Example of fetching a scoped token at startup
func getScopedToken() (string, error) {
    // Call a vault or identity provider
    return "scoped-token", nil
}