Overview
SSRF in Go (Gin) can allow an attacker to coerce the server into making requests to arbitrary hosts, including internal services. In Gin apps that accept a user-supplied URL and fetch it server-side, this can bypass client-side protections and reach sensitive endpoints or internal networks. The risk scales with proxies, data fetchers, or image loaders that reflect or forward fetched content back to the client.
In real-world deployments, SSRF can target cloud metadata endpoints, internal DNS, or services behind firewalls. Go's net/http client will resolve hosts, follow redirects, and potentially expose internal infrastructure if input is not restricted. When used in a web route, this class of vulnerability can enable information gathering, lateral movement, or access control bypass.
This guide describes how SSRF manifests in Go with Gin and provides concrete mitigations: validate and constrain user-provided URLs, implement a host allowlist or DNS allow rules, disable redirects and proxies, and configure a dedicated HTTP client with strict timeouts and connection limits. It also covers logging, monitoring, and testing practices to prevent regressions.
Note: No CVE IDs are provided here; apply these defenses to reduce risks associated with SSRF in Go/Gin applications, following standard security patterns for outbound requests.
Code Fix Example
Go (Gin) API Security Remediation
package main
import (
"io"
"net/http"
"net/url"
"time"
"github.com/gin-gonic/gin"
)
const vulnPath = "/vuln"
const fixPath = "/fix"
func main() {
r := gin.Default()
r.GET(vulnPath, vulnHandler)
r.GET(fixPath, fixHandler)
r.Run()
}
func vulnHandler(c *gin.Context) {
raw := c.Query("url")
resp, err := http.Get(raw) // vulnerable: user-controlled URL
if err != nil {
c.String(500, err.Error())
return
}
defer resp.Body.Close()
body, _ := io.ReadAll(resp.Body)
c.Data(resp.StatusCode, "text/plain", body)
}
func fixHandler(c *gin.Context) {
raw := c.Query("url")
u, err := url.Parse(raw)
if err != nil || (u.Scheme != "http" && u.Scheme != "https") {
c.String(400, "invalid url"); return
}
allowed := map[string]bool{
"example.com": true,
"cdn.example.org": true,
}
if !allowed[u.Hostname()] {
c.String(403, "host not allowed"); return
}
transport := &http.Transport{ Proxy: nil }
client := &http.Client{ Timeout: 5 * time.Second, Transport: transport, CheckRedirect: func(req *http.Request, via []*http.Request) error { return http.ErrUseLastResponse } }
resp, err := client.Get(raw)
if err != nil {
c.String(500, err.Error())
return
}
defer resp.Body.Close()
body, _ := io.ReadAll(resp.Body)
c.Data(resp.StatusCode, "text/plain", body)
}