Overview
SSRF vulnerabilities in Go applications using Gin can enable attackers to force the server to fetch resources from internal networks, cloud metadata endpoints, or other protected services. This can lead to data exfiltration, credential exposure, or service disruption, especially in multi-tenant or cloud environments where internal addresses are reachable from the host.
In Go with Gin, SSRF often arises when a handler reads a user controlled URL and uses it to perform outbound requests without validating the destination, end points, or network path. This risk grows when redirects or proxies are involved and when the destination list is not restricted.
Mitigations focus on input validation and network controls. Use explicit allowlists for hosts and schemes, verify that resolved IPs are not private, and block internal addresses. Consider routing outbound requests through a controlled gateway and enforce strict timeouts and logging.
Remediation patterns shown below illustrate a vulnerable pattern and a safe fix, with the fix applying host allowlisting, private IP filtering, and restricted redirects to eliminate SSRF risk.
Code Fix Example
Go (Gin) API Security Remediation
package main
import (
`io`
`net`
`net/http`
`net/url`
gin `github.com/gin-gonic/gin`
)
func vulnerableHandler(c *gin.Context) {
target := c.Query(`target`)
if target == `` {
c.String(400, `missing target`)
return
}
resp, err := http.Get(target)
if err != nil {
c.String(500, `error fetching target`)
return
}
defer resp.Body.Close()
b, _ := io.ReadAll(resp.Body)
c.String(resp.StatusCode, string(b))
}
func isPrivateIP(ip net.IP) bool {
privateCIDRs := []string{`10.0.0.0/8`, `172.16.0.0/12`, `192.168.0.0/16`, `127.0.0.0/8`}
for _, cidr := range privateCIDRs {
_, block, _ := net.ParseCIDR(cidr)
if block.Contains(ip) {
return true
}
}
return false
}
func fixedHandler(c *gin.Context) {
target := c.Query(`target`)
if target == `` {
c.String(400, `missing target`)
return
}
u, err := url.Parse(target)
if err != nil || (u.Scheme != `http` && u.Scheme != `https`) {
c.String(400, `invalid url`)
return
}
switch u.Host {
case `example.com`, `api.example.com`:
// allowed
default:
c.String(403, `forbidden host`)
return
}
ips, err := net.LookupIP(u.Hostname())
if err == nil {
for _, ip := range ips {
if isPrivateIP(ip) {
c.String(403, `private IPs not allowed`)
return
}
}
}
req, _ := http.NewRequest(http.MethodGet, target, nil)
client := &http.Client{ CheckRedirect: func(req *http.Request, via []*http.Request) error {
return http.ErrUseLastResponse
} }
resp, err := client.Do(req)
if err != nil {
c.String(500, `error fetching target`)
return
}
defer resp.Body.Close()
b, _ := io.ReadAll(resp.Body)
c.String(resp.StatusCode, string(b))
}
func main() {
r := gin.Default()
r.GET(`/vuln`, vulnerableHandler)
r.GET(`/fix`, fixedHandler)
r.Run(`:8080`)
}