Overview
CVE-2026-33039 describes an SSRF flaw in WWBN AVideo where an endpoint validates only the initial user-supplied URL against internal/private networks, but then follows redirects without re-validating the redirect target. In Go (Gin) contexts, a similar pattern can occur if you validate the first URL with a function like isSSRFsafeURL() and then rely on the standard http client to follow redirects automatically. An attacker can craft a URL that initially points to a safe surface but redirects to internal endpoints (e.g., RFC1918 addresses or cloud metadata services) which are then accessed by the server, leading to unauthorized access to internal services. This class of vulnerability maps to CWE-918 (Server-Side Request Forgery) and mirrors the real-world impact of CVE-2026-33039, where the final target accessed after a redirect was not re-validated, enabling access to internal resources via attacker-controlled redirects. The 26.0 release of WWBN AVideo fixes this by addressing the redirect handling behavior. In Go/Gin-based services, applying the same lesson-validate every URL encountered in a redirect chain and constrain redirections-helps prevent similar SSRF scenarios under CGIs, microservices, or API proxies.
Affected Versions
25.0 and below vulnerable; fixed in 26.0
Code Fix Example
Go (Gin) API Security Remediation
package main
import (
"io"
"net"
"net/http"
"net/url"
"time"
"strings"
"github.com/gin-gonic/gin"
)
func isSSRFsafeURL(raw string) bool {
u, err := url.Parse(raw)
if err != nil {
return false
}
if u.Scheme != "http" && u.Scheme != "https" {
return false
}
host := u.Hostname()
// If host is an IP, reject private/local addresses
if ip := net.ParseIP(host); ip != nil {
if ip.IsLoopback() || ip.IsPrivate() || ip.IsLinkLocalUnicast() {
return false
}
} else {
lower := strings.ToLower(host)
if lower == "localhost" {
return false
}
if strings.HasPrefix(lower, "10.") || strings.HasPrefix(lower, "192.168.") || strings.HasPrefix(lower, "172.") {
return false
}
if host == "169.254.169.254" {
return false
}
}
return true
}
// Vulnerable pattern: validate only the initial URL, then follow redirects implicitly
func vulnerableHandler(c *gin.Context) {
target := c.Query("url")
if target == "" {
c.JSON(400, gin.H{"error": "missing url"})
return
}
if !isSSRFsafeURL(target) {
c.JSON(400, gin.H{"error": "untrusted url"})
return
}
resp, err := http.Get(target) // follows redirects with no per-redirect validation
if err != nil {
c.JSON(500, gin.H{"error": err.Error()})
return
}
defer resp.Body.Close()
body, _ := io.ReadAll(resp.Body)
c.Data(resp.StatusCode, resp.Header.Get("Content-Type"), body)
}
// Fixed pattern: validate every redirect target by using a custom CheckRedirect
func fixedHandler(c *gin.Context) {
target := c.Query("url")
if target == "" {
c.JSON(400, gin.H{"error": "missing url"})
return
}
client := &http.Client{
CheckRedirect: func(req *http.Request, via []*http.Request) error {
if !isSSRFsafeURL(req.URL.String()) {
return http.ErrUseLastResponse
}
if len(via) >= 10 {
return http.ErrUseLastResponse
}
return nil
},
Timeout: 10 * time.Second,
}
resp, err := client.Get(target)
if err != nil {
c.JSON(500, gin.H{"error": err.Error()})
return
}
defer resp.Body.Close()
body, _ := io.ReadAll(resp.Body)
c.Data(resp.StatusCode, resp.Header.Get("Content-Type"), body)
}
func main() {
r := gin.Default()
r.GET("/vuln", vulnerableHandler)
r.GET("/fix", fixedHandler)
r.Run(":8080")
}