Overview
The CVE-2026-41905 entry describes a server-side request forgery issue in FreeScout where an initial host check is bypassed by following redirects and revalidating the original URL instead of the final redirect destination. This allowed attackers to supply a URL that passes the initial host check and then redirect the server to internal HTTP services or RFC1918 addresses that should be blocked. The vulnerability is tracked under CWE-918 and was patched in FreeScout version 1.8.217. In Go applications using the Gin framework, a similar SSRF risk arises when a service accepts a user-provided URL and fetches it by following redirects, but only validates the host of the initial URL. If the final destination after redirects is not validated, an attacker can route requests to internal resources (metadata endpoints, private APIs, internal networks). This class of vulnerability is a real-world risk for services that proxy or fetch arbitrary user URLs.
In Go (Gin), SSRF scenarios occur when an endpoint takes a query parameter or body URL, performs an HTTP request, and relies on an initial host check while allowing redirects to take the request to an internal resource. If final destinations are not validated, an attacker can leverage redirect chains to reach internal services or metadata endpoints, undermining network segmentation and exposing sensitive data. This mirrors the CVE-2026-41905 pattern and aligns with CWE-918. The remediation is to validate both the initial target and every redirect destination, or to constrain redirects altogether, ensuring that only approved hosts are reachable by the server.
Code Fix Example
Go (Gin) API Security Remediation
package main
import (
"io"
"net/http"
"net/url"
"github.com/gin-gonic/gin"
)
func isAllowed(host string) bool {
allowed := map[string]bool{
"example.com": true,
"api.example.com": true,
}
return allowed[host]
}
// Vulnerable pattern: validates only the initial URL's host, then follows redirects without validating the final destination
func vulnerableFetch(c *gin.Context) {
raw := c.Query("url")
u, err := url.Parse(raw)
if err != nil {
c.String(400, "invalid url")
return
}
// Initial host check only
if !isAllowed(u.Host) {
c.String(400, "host not allowed")
return
}
resp, err := http.Get(raw) // follows redirects automatically
if err != nil {
c.String(500, err.Error())
return
}
defer resp.Body.Close()
body, _ := io.ReadAll(resp.Body)
c.Data(200, "text/plain", body)
}
// Fixed pattern: validate each redirect destination or disable redirects
func fixedFetch(c *gin.Context) {
raw := c.Query("url")
// Optionally re-parse to confirm validity
if _, err := url.Parse(raw); err != nil {
c.String(400, "invalid url")
return
}
client := &http.Client{
CheckRedirect: func(req *http.Request, via []*http.Request) error {
// Validate every redirect destination
if !isAllowed(req.URL.Host) {
return http.ErrUseLastResponse
}
return nil
},
}
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(200, "text/plain", body)
}
func main() {
r := gin.Default()
r.GET("/vuln", vulnerableFetch)
r.GET("/fix", fixedFetch)
r.Run(":8080")
}