Overview
SSRF vulnerabilities in Echo can enable attackers to make the server initiate requests to internal or otherwise restricted resources. This can lead to exposure of internal networks, access to cloud metadata services, unintended interactions with other services, or exfiltration of data. In real-world scenarios, an endpoint that fetches or proxies a client-supplied URL can be abused to reach sensitive endpoints, bypass access controls, or perform network reconnaissance from within your application's trusted environment. Mirrored risk includes abuse of metadata endpoints and potential privilege escalation through subsequent, targeted requests. No CVEs are provided for this guide, but the class of vulnerability remains a critical SSRF risk in apps like Echo when user input controls outbound requests.
In Echo, SSRF typically manifests when a handler uses a user-provided URL to perform outbound requests (for example, via http.Get on a query parameter) without validating the destination. Echo handlers run with the server's network privileges, so an attacker can direct traffic toward internal hosts, admin interfaces, or external services that should be blocked. This can lead to data access, lateral movement, or hidden data egress. Proper validation, strict allowlists, and controlled outbound fetch logic are essential to mitigate this risk in Echo-based services.
This guide outlines practical remediation: avoid fetching client-controlled URLs directly; introduce a strict allowlist or a dedicated outbound fetch helper that enforces host validation; apply network egress controls, timeouts, and safe HTTP client configurations; and implement robust error handling to avoid leaking internal details. After implementing fixes, add targeted tests that simulate SSRF payloads and audit Echo routes that perform outbound requests to ensure ongoing protection as dependencies evolve.
Code Fix Example
Echo API Security Remediation
package main
import (
"io"
"net/http"
"net/url"
"strings"
"github.com/labstack/echo/v4"
)
func main() {
e := echo.New()
e.GET(`/vuln-fetch`, vulnerableFetchHandler)
e.GET(`/safe-fetch`, safeFetchHandler)
e.Start(`:8080`)
}
// Vulnerable pattern
func vulnerableFetchHandler(c echo.Context) error {
raw := c.QueryParam(`url`)
if raw == `` {
return c.String(http.StatusBadRequest, `missing url`)
}
resp, err := http.Get(raw)
if err != nil {
return c.String(http.StatusBadGateway, err.Error())
}
defer resp.Body.Close()
body, _ := io.ReadAll(resp.Body)
return c.String(http.StatusOK, string(body))
}
// Fixed pattern
func safeFetchHandler(c echo.Context) error {
raw := c.QueryParam(`url`)
if raw == `` { return c.String(http.StatusBadRequest, `missing url`) }
u, err := url.Parse(raw)
if err != nil { return c.String(http.StatusBadRequest, `invalid url`) }
if u.Scheme != `http` && u.Scheme != `https` { return c.String(http.StatusBadRequest, `unsupported scheme`) }
host := u.Hostname()
if !strings.EqualFold(host, `example.com`) && !strings.EqualFold(host, `api.example.com`) {
return c.String(http.StatusForbidden, `host not allowed`)
}
resp, err := http.Get(raw)
if err != nil { return c.String(http.StatusBadGateway, err.Error()) }
defer resp.Body.Close()
body, _ := io.ReadAll(resp.Body)
ct := resp.Header.Get(`Content-Type`)
return c.Blob(http.StatusOK, ct, body)
}