Overview
SSRF vulnerabilities in Go applications using the Gin framework typically arise when the server fetches resources specified by a user input, such as a URL parameter, without proper validation. An attacker can abuse this behavior to make the server reach internal services, cloud metadata endpoints, or other resources that are not intended to be exposed to external callers. Depending on the target, this can lead to information disclosure, port scanning of internal services, or even broader network access that could enable lateral movement within a cloud environment. In cloud environments, SSRF can be leveraged to access instance metadata services, attacker-controlled internal endpoints, or services protected by private networks. As with other server-side actions, the risk is not just data leakage; it can enable more sophisticated exploitation chains if the server can interact with internal resources on behalf of an attacker.
Code Fix Example
Go (Gin) API Security Remediation
package main
import (
"io/ioutil"
"net/http"
"net/url"
"time"
"github.com/gin-gonic/gin"
)
func vulnerableFetch(c *gin.Context) {
target := c.Query("target") // user-provided URL
resp, err := http.Get(target)
if err != nil {
c.String(500, "error")
return
}
defer resp.Body.Close()
body, _ := ioutil.ReadAll(resp.Body)
c.String(resp.StatusCode, string(body))
}
var allowedHosts = map[string]struct{}{
"example.com": {},
"api.example.com": {},
}
func isAllowed(u *url.URL) bool {
host := u.Hostname()
if _, ok := allowedHosts[host]; ok {
return true
}
return false
}
func safeFetch(c *gin.Context) {
raw := c.Query("target")
parsed, err := url.Parse(raw)
if err != nil || !parsed.IsAbs() {
c.String(400, "invalid url")
return
}
if !isAllowed(parsed) {
c.String(403, "destination not allowed")
return
}
client := &http.Client{ Timeout: 5 * time.Second }
client.CheckRedirect = func(req *http.Request, via []*http.Request) error {
return http.ErrUseLastResponse
}
resp, err := client.Get(raw)
if err != nil {
c.String(502, "bad gateway")
return
}
defer resp.Body.Close()
body, _ := ioutil.ReadAll(resp.Body)
c.String(resp.StatusCode, string(body))
}
func main() {
r := gin.Default()
r.GET("/fetch", vulnerableFetch) // vulnerable
r.GET("/safe-fetch", safeFetch) // fixed
_ = r.Run(":8080")
}