Open Redirect in Buffalo with Dynamodb

An open redirect in a Buffalo application that uses DynamoDB for session or user data can occur when a redirect target is derived from untrusted input and the application relies on DynamoDB to validate or retrieve redirect metadata. For example, a handler might read a redirect_url property from a DynamoDB item based on a user-supplied key, then pass that value directly to Buffalo’s redirection functions without strict allowlisting. Because DynamoDB stores configuration or mapping data, an attacker who can influence the key (e.g., via IDOR or BOLA) may be able to cause the application to fetch a malicious URL stored in DynamoDB or to reflect attacker-controlled input into the redirect response.

The risk is compounded when the application uses DynamoDB to implement feature flags or per-user redirect mappings without enforcing strict schema validation. If the application trusts the contents of DynamoDB and does not enforce an allowlist of safe domains, an attacker who can write or read arbitrary DynamoDB items may be able to pivot from data access to client-side phishing or token theft via open redirect. This pattern is relevant to checks such as BOLA/IDOR, Property Authorization, and Input Validation, which middleBrick tests in parallel to surface unsafe consumption of DynamoDB data that can lead to open redirects.

In practice, an open redirect does not directly compromise the server, but it can be used to degrade trust in the application and facilitate further attacks like credential phishing. MiddleBrick’s checks for Input Validation and Property Authorization help detect whether redirect values sourced from DynamoDB are properly constrained, and its findings include remediation guidance to ensure that redirects are safe regardless of the data source.

To remediate open redirect risks when using DynamoDB with Buffalo, ensure that any redirect target stored in or retrieved from DynamoDB is strictly validated against an allowlist of permitted hosts. Do not rely on client-supplied values to determine the redirect destination, and avoid storing arbitrary URLs in DynamoDB unless they are required and governed by strict validation.

Example: Safe redirect with DynamoDB lookup in Buffalo

Assume you store allowed redirect targets keyed by an identifier in DynamoDB. Use strong typing, schema validation on read, and an allowlist check before redirecting.

// models/redirect_target.go
package models

type RedirectTarget struct {
	ID          string `json:"id"`
	Destination string `json:"destination"` // Must be a full URL
}

// Validate ensures the destination is allowed.
func (r RedirectTarget) Validate() error {
	// Allowlist of permitted hosts
	allowed := map[string]bool{
		"https://app.example.com": true,
		"https://docs.example.com": true,
	}
	if !allowed[r.Destination] {
		return errors.New("destination not allowed")
	}
	return nil
}

// handlers/redirects.go
package handlers

import (
	"github.com/gobuffalo/buffalo"
	"your-app/models"
)

func RedirectHandler(c buffalo.Context) error {
	key := c.Param("key")
	var target models.RedirectTarget

	// Fetch item from DynamoDB using a key that is validated and scoped to the requester.
	// Example uses a hypothetical DynamoDB helper; adapt to your DB layer.
	err := app.DynamoDB.GetByKey(key, &target)
	if err != nil {
		c.Response().WriteHeader(404)
		return c.Render(404, r.H{"error": "not found"})
	}

	// Validate against allowlist before redirecting.
	if err := target.Validate(); err != nil {
		c.Response().WriteHeader(400)
		return c.Error(400, err)
	}

	// Safe, validated redirect.
	c.Response().Header().Set("Location", target.Destination)
	c.Response().WriteHeader(302)
	return nil
}

Additional practices:

• Do not store arbitrary user-supplied URLs in DynamoDB; if necessary, store only path segments and construct absolute URLs server-side using a known base domain.
• Enforce strict schema validation when writing to DynamoDB so that only properly formed, allowed destinations can be stored.
• Apply the same origin checks on the client side where relevant, but never rely on client enforcement for security-critical decisions.

By combining DynamoDB with disciplined allowlisting and validation, you reduce the risk that data retrieved during a scan triggers an open redirect. middleBrick’s checks for Input Validation and Property Authorization will highlight whether such unsafe patterns exist in your API surface.