Ssrf in Buffalo with Jwt Tokens

Server-Side Request Forgery (SSRF) in the Buffalo framework becomes especially risky when applications embed JWT tokens in outgoing HTTP requests. Buffalo does not inherently manage or validate tokens for external service calls, so developer code that constructs HTTP requests with JWTs can unintentionally expose internal endpoints or bypass network-level isolation. A typical pattern is using http.Client or a third-party client to call an external API and adding an Authorization header containing a JWT. If the target URL is derived from user input without strict validation, an attacker can direct the request to internal metadata services (e.g., http://169.254.169.254 on cloud environments) while the JWT is forwarded, potentially escalating the impact by accessing protected resources that trust the token.

In Buffalo, a vulnerable handler might look like accepting a URL from a query parameter, appending a JWT collected from the current session or a configuration value, and issuing a GET request. Because SSRF testing is one of the 12 parallel security checks in middleBrick, such flows can be detected when unauthenticated scanning reveals endpoints that allow SSRF via manipulated URLs and exposed Authorization headers. The presence of JWTs does not cause SSRF, but it can amplify the severity by enabling access to internal services that accept the token. Attack patterns like metadata retrieval, internal service enumeration, or SSRF-to-SSRF pivots become feasible when the token is automatically included in outbound calls without validating the destination.

Real-world examples include calling an external OAuth introspection endpoint with a JWT and allowing the user to specify the introspection URL, or using a webhook URL provided by an attacker that points to an internal listener expecting a JWT. Because Buffalo applications often integrate with external APIs using tokens, developers must ensure that user-controlled inputs cannot redirect requests to internal network locations. middleBrick’s checks for SSRF and Inventory Management help surface these risks by correlating runtime behavior with OpenAPI specifications, even when requests include JWT headers.

Remediation focuses on input validation, avoiding automatic propagation of JWTs to external calls, and explicitly managing which requests carry tokens. Never forward user-supplied URLs directly into HTTP clients that also attach session or service JWTs. Instead, maintain an allowlist of trusted endpoints, use separate HTTP clients without sensitive headers for untrusted targets, and validate hostnames and schemes rigorously.

Example: Safe external call without leaking session JWT

// Do NOT do this: forwarding user input with the session JWT
func (r MyController) UnsafeAction(c buffalo.Context) error {
    userURL := c.Param("url") // UNSAFE: user-controlled
    jwt := c.Get("current_jwt") // session token
    client := &http.Client{}
    req, _ := http.NewRequest("GET", userURL, nil)
    req.Header.Set("Authorization", "Bearer " + jwt)
    resp, err := client.Do(req)
    // Risk: SSRF to internal services with valid JWT
    return c.Render(200, r.JSON(resp))
}

// Do this: validate and use a separate client without sensitive headers
func (r MyController) SafeAction(c buffalo.Context) error {
    userURL := c.Param("url")
    if !isValidExternalURL(userURL) {
        return c.Error(400, errors.New("invalid target"))
    }
    // Client without Authorization header for external calls
    client := &http.Client{}
    resp, err := client.Get(userURL)
    if err != nil {
        return c.Error(500, err)
    }
    defer resp.Body.Close()
    return c.Render(200, r.JSON(resp))
}

func isValidExternalURL(raw string) bool {
    u, err := url.Parse(raw)
    if err != nil {
        return false
    }
    // Allow only specific schemes and host patterns
    if u.Scheme != "https" {
        return false
    }
    // Example: restrict to known external APIs
    allowedHosts := map[string]bool{"api.example.com": true, "auth.partner.com": true}
    if !allowedHosts[u.Host] {
        return false
    }
    return true
}

Example: Controlled token introspection with explicit JWT usage

// Explicitly manage which call carries the JWT
func (r MyController) IntrospectToken(c buffalo.Context) error {
    // Assume we have a validated external service URL
    const introspectionURL = "https://auth.example.com/introspect"
    jwt := c.Get("current_jwt")
    payload := url.Values{}
    payload.Set("token", jwt)
    payload.Set("active", "true")
    resp, err := http.PostForm(introspectionURL, payload)
    if err != nil {
        return c.Error(500, err)
    }
    defer resp.Body.Close()
    // Process response without propagating user input as URL
    var result map[string]interface{}
    json.NewDecoder(resp.Body).Decode(&result)
    return c.Render(200, r.JSON(result))
}

These patterns ensure that JWTs are not automatically attached to requests whose targets are influenced by user input. For continuous assurance, middleBrick can be used via the CLI (middlebrick scan <url>) or integrated into CI/CD with the GitHub Action to fail builds if risk scores degrade, while the Dashboard helps track security findings over time.