Overview
SSRF in Gin-based Go applications occurs when the server fetches a URL supplied by a client. If the URL points to an internal service or a cloud metadata endpoint, an attacker can cause the application to access internal resources, potentially leaking credentials, performing port scanning, or reaching services that should be hidden behind a firewall.
In Go with the Gin framework, SSRF typically manifests when a handler reads a URL from a request parameter or JSON field and uses http.Get, http.Client.Do, or similar calls without validating the destination. Gin does not automatically protect against this; the risk arises from the server acting on behalf of the client.
Impact can include accessing cloud provider metadata, internal REST services, or other internal endpoints. Attackers can use this to enumerate internal services or exfiltrate data. Proper timeouts can help limit damage, but they do not substitute for proper input validation and network egress controls.
No CVEs are referenced in this guide. This is a general remediation guide based on known SSRF patterns in this framework. The following code demonstrates the vulnerable pattern and a mitigated version.
Code Fix Example
Go (Gin) API Security Remediation
package main
import (
`fmt`
`io`
`net`
`net/http`
`net/url`
`time`
`github.com/gin-gonic/gin`
)
func main() {
r := gin.Default()
r.GET(`/vuln-fetch`, func(c *gin.Context) {
target := c.Query(`url`)
data, err := fetchVulnerable(target)
if err != nil { c.String(500, `error`); return }
c.Data(200, `text/plain`, data)
})
r.GET(`/fix-fetch`, func(c *gin.Context) {
target := c.Query(`url`)
data, err := fetchFixed(target)
if err != nil { c.String(500, err.Error()) ; return }
c.Data(200, `text/plain`, data)
})
r.Run(`:8080`)
}
// Vulnerable pattern: directly fetch user-provided URL
func fetchVulnerable(target string) ([]byte, error) {
resp, err := http.Get(target)
if err != nil { return nil, err }
defer resp.Body.Close()
return io.ReadAll(resp.Body)
}
// Fixed fetch with SSRF mitigations
func fetchFixed(target string) ([]byte, error) {
u, err := url.Parse(target)
if err != nil { return nil, err }
if u.Scheme != `http` && u.Scheme != `https` {
return nil, fmt.Errorf(`unsupported URL scheme: %s`, u.Scheme)
}
host := u.Hostname()
ips, err := net.LookupIP(host)
if err != nil { return nil, err }
for _, ip := range ips {
if isPrivateIP(ip) { return nil, fmt.Errorf(`refusing private IP: %s`, ip) }
}
client := &http.Client{ Timeout: 10 * time.Second }
resp, err := client.Get(target)
if err != nil { return nil, err }
defer resp.Body.Close()
return io.ReadAll(resp.Body)
}
func isPrivateIP(ip net.IP) bool {
if ip4 := ip.To4(); ip4 != nil {
switch {
case ip4[0] == 10:
return true
case ip4[0] == 172 && ip4[1] >= 16 && ip4[1] <= 31:
return true
case ip4[0] == 192 && ip4[1] == 168:
return true
case ip4[0] == 127:
return true
default:
return false
}
}
if ip.IsLoopback() { return true }
if ip.To16() != nil && ip[0] == 0xfd { return true }
return false
}