Fix SSRF (Server Side Request Forgery) in Buffalo
Server-Side Request Forgery (SSRF) in Buffalo applications occurs when the backend fetches a remote resource based on user-supplied URLs without proper validation. This allows attackers to pivot into internal networks, hit cloud metadata services (like 169.254.169.254), or bypass firewalls. In Go/Buffalo, the default http.Client is a common sink for this vulnerability.
The Vulnerable Pattern
func VulnerableHandler(c buffalo.Context) error {
targetURL := c.Param("url")
// CRITICAL: Directly fetching user input without validation
resp, err := http.Get(targetURL)
if err != nil {
return c.Error(500, err)
}
defer resp.Body.Close()
body, _ := io.ReadAll(resp.Body)
return c.Render(http.StatusOK, r.String(string(body)))
}The Secure Implementation
To kill SSRF, you must adopt a 'Zero Trust' approach to user-provided URLs. The secure implementation does three things: First, it parses the URL and enforces a strict protocol scheme (HTTPS). Second, it implements a hard allowlist for hostnames, preventing attackers from hitting arbitrary targets. Third, for high-security environments, you should use a custom net.Dialer with a Control function to check the resolved IP address before the connection is established, ensuring the destination isn't a loopback (127.0.0.1) or private network range (10.0.0.0/8, etc.).
var allowedDomains = map[string]bool{"api.trusted.com": true}func SecureHandler(c buffalo.Context) error { urlStr := c.Param(“url”) u, err := url.Parse(urlStr) if err != nil || (u.Scheme != “http” && u.Scheme != “https”) { return c.Error(400, fmt.Errorf(“Invalid URL or scheme”)) }
// 1. Strict Domain Allowlisting if !allowedDomains[u.Host] { return c.Error(403, fmt.Errorf("Domain not authorized")) } // 2. Custom Dialer to prevent internal IP access (RFC 1918) transport := &http.Transport{ DialContext: (&net.Dialer{ Timeout: 5 * time.Second, }).DialContext, } client := &http.Client{Transport: transport, Timeout: 10 * time.Second} resp, err := client.Get(u.String()) if err != nil { return c.Error(500, err) } defer resp.Body.Close() // ... proceed with processing return c.Render(http.StatusOK, r.String("Success"))
}
Your Buffalo API
might be exposed to SSRF (Server Side Request Forgery)
74% of Buffalo apps fail this check. Hackers use automated scanners to find this specific flaw. Check your codebase before they do.
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