Ssrf in Buffalo with Basic Auth

Server-Side Request Forgery (SSRF) in Buffalo occurs when an attacker can coerce the server into making arbitrary HTTP requests. In Buffalo, this typically arises when user-controlled input is used to construct URLs for HTTP clients without adequate validation or network controls. When Basic Authentication credentials are embedded in these requests, the exposure becomes more severe: leaked credentials, unintended access to internal services, and potential lateral movement within a protected network.

Consider a Buffalo application that accepts a URL parameter to proxy or fetch external resources, for example to retrieve a remote configuration or webhook delivery. If the developer builds the request using user input and attaches an Authorization header derived from a static service account, an attacker can supply a malicious URL pointing to internal endpoints (e.g., http://169.254.169.254/latest/meta-data/ or internal services like http://redis:6379). Because the request runs with the embedded Basic Auth credentials, the SSRF can be used to authenticate to otherwise restricted internal services, retrieve sensitive data, or perform actions the service account is permitted to do. The combination of SSRF and Basic Auth means that even if the endpoint is behind a firewall or internal-only, the attacker can pivot using valid credentials supplied by the application.

In a real scenario, suppose the application constructs a request like this based on a user-supplied URL:

req, err := http.NewRequest("GET", userURL, nil)
req.SetBasicAuth("svcAccount", "SuperSecret123")
resp, err := http.DefaultClient.Do(req)

If userURL is not properly validated and an attacker provides http://localhost:9090/debug/vars, the request will include the Basic Auth header and reach an internal debug endpoint. This exposes both the ability to trigger SSRF and the misuse of Basic Auth for internal service impersonation. MiddleBrick scans detect such patterns by correlating unauthenticated endpoint testing with OpenAPI specifications and runtime findings; the tool flags exposed authentication in SSRF contexts and highlights risks like credential leakage and unauthorized internal access, which align with OWASP API Top 10 and common compliance mappings.

Buffalo applications often use middleware or client wrappers to centralize HTTP calls. If these components accept a target URL and inject Basic Auth automatically, they become a single point of failure. The framework’s convention-based routing and parameter handling do not inherently protect against malicious URLs, so developers must treat external input as hostile even when credentials are managed server-side. An effective detection strategy includes validating hostnames against an allowlist, disabling redirects for sensitive endpoints, and ensuring that authentication is applied selectively rather than blanket-attached to all outbound requests.

To remediate SSRF with Basic Auth in Buffalo, focus on input validation, credential isolation, and network controls. Avoid constructing requests with user-controlled URLs, and if necessary, enforce strict allowlists for hosts and ports. Do not embed Basic Auth credentials in requests that can be influenced by the user; instead, use scoped tokens or server-side secrets with limited lifetimes. When Basic Auth must be used, ensure it is applied only to trusted endpoints and never forwarded to arbitrary user-defined targets.

Below are concrete code examples demonstrating secure handling in Buffalo. The first example shows a vulnerable pattern that should be avoided:

// Vulnerable: user-controlled URL with embedded Basic Auth
func SomeHandler(c buffalo.Context) error {
    userURL := c.Param("url")
    req, _ := http.NewRequest("GET", userURL, nil)
    req.SetBasicAuth("svcAccount", "SuperSecret123") // Credential leak risk
    client := &http.Client{CheckRedirect: func(req *http.Request, via []*http.Request) error {
        return http.ErrUseLastResponse
    }}
    resp, err := client.Do(req)
    // ...
}

A secure alternative validates the target host and uses a restricted client configuration:

// Secure: host allowlist and no dynamic Basic Auth
var allowedHosts = map[string]bool{
    "api.external.com": true,
    "config.example.org": true,
}

func buildClientForTrustedHost(target string) (*http.Client, error) {
    u, err := url.Parse(target)
    if err != nil {
        return nil = err
    }
    if !allowedHosts[u.Host] {
        return nil = fmt.Errorf("host not allowed")
    }
    client := &http.Client{
        CheckRedirect: func(req *http.Request, via []*http.Request) error {
            return http.ErrUseLastResponse
        },
    }
    return client, nil
}

func SafeHandler(c buffalo.Context) error {
    target := c.Param("target")
    client, err := buildClientForTrustedHost(target)
    if err != nil {
        return c.Render(400, r.Text("Invalid target"))
    }
    // Use a static, scoped credential or token for this trusted endpoint
    req, _ := http.NewRequest("GET", target, nil)
    req.Header.Set("Authorization", "Bearer scoped-token-with-limited-permissions")
    resp, err := client.Do(req)
    // Handle response
    return nil
}

Additional measures include disabling redirects for sensitive flows, using url.Host validation to prevent hostname confusion attacks, and ensuring that credentials are sourced from secure configuration or Vault rather than hardcoded. MiddleBrick’s scans can surface insecure patterns like dynamic credential attachment and missing host allowlists, enabling teams to remediate before exposure.