Ssrf in Buffalo with Dynamodb

Server-Side Request Forgery (SSRF) in a Buffalo application that interacts with Amazon DynamoDB can occur when untrusted input is used to construct HTTP requests or AWS SDK operations, allowing an attacker to make the server access internal or unintended resources. In this context, the combination is specific because Buffalo applications typically manage backend logic and database interactions in Go, and DynamoDB is often accessed through the AWS SDK for Go (v2). If user-supplied data—such as a URL, region, or endpoint—is used to influence SDK configuration or HTTP client behavior without strict validation, the server may be coerced into making requests to internal AWS metadata services or other internal endpoints.

For example, an attacker might supply a specially crafted parameter that causes the application to request instance metadata (e.g., http://169.254.169.254/latest/meta-data/iam/security-credentials/) via the same networking path used for legitimate DynamoDB calls. If the application uses a custom HTTP client or proxy settings influenced by user input when initializing the DynamoDB client, SSRF can be leveraged to probe internal services. Because DynamoDB operations are signed requests, SSRF does not require AWS credentials to trigger internal probing; it abuses the application’s ability to reach unexpected endpoints through manipulated inputs that affect request construction or client configuration.

middleBrick detects this pattern during unauthenticated scans by analyzing the surface presented by the API and observing behaviors that indicate the application can be directed to make internal or external requests under attacker control. Because SSRF often maps to OWASP API Top 10 #1 (Broken Object Level Authorization) and can facilitate data exposure or further internal compromise, it is critical to validate and sanitize any inputs that influence network destinations or SDK configuration in Buffalo applications using DynamoDB.

To remediate SSRF in a Buffalo application that uses DynamoDB, ensure that all user-controlled inputs are strictly validated and never used to directly influence HTTP client settings, proxy configurations, or endpoint overrides for the AWS SDK. Use allowlists for expected values, avoid passing raw user input into SDK configuration fields, and prefer hardcoded or configuration-managed endpoints. Below are concrete Go code examples using the AWS SDK for Go v2 within a Buffalo application.

Example 1: Safe DynamoDB client initialization without user-influenced endpoints

// Safe: DynamoDB client uses default AWS configuration without user-supplied endpoint override.
package app

import (
	"context"
	"github.com/aws/aws-sdk-go-v2/aws"
	"github.com/aws/aws-sdk-go-v2/config"
	"github.com/aws/aws-sdk-go-v2/service/dynamodb"
	"github.com/gobuffalo/buffalo"
)

func NewDynamoClient() (*dynamodb.Client, error) {
	// Load SDK config from environment, shared config, or explicit AWS config sources.
	// Do not allow user input to set the endpoint here.
	cfg, err := config.LoadDefaultConfig(context.TODO())
	if err != nil {
		return nil, err
	}
	return dynamodb.NewFromConfig(cfg), nil
}

func ItemsHandler(c buffalo.Context) error {
	client, err := NewDynamoClient()
	if err != nil {
		return c.Error(500, err)
	}

	// Example safe GetItem using validated keys only.
	input := &dynamodb.GetItemInput{
		TableName: aws.String("ItemsTable"),
		Key: map[string]aws.AttributeValue{
			"ID": &dynamodb.AttributeValueMemberS{Value: c.Param("id")},
		},
	}

	out, err := client.GetItem(c.Request().Context(), input)
	if err != nil {
		return c.Error(500, err)
	}

	return c.Render(200, r.JSON(out.Item))
}

Example 2: Validating and using user input for key attributes only

// Validate user input against an allowlist or strict format before using in DynamoDB operations.
package app

import (
	"regexp"
	"github.com/aws/aws-sdk-go-v2/service/dynamodb"
)

var safeIDRegex = regexp.MustCompile(`^[A-Za-z0-9_-]{1,64}$`)

func IsValidItemID(id string) bool {
	return safeIDRegex.MatchString(id)
}

func UpdateHandler(c buffalo.Context) error {
	itemID := c.Param("id")
	if !IsValidItemID(itemID) {
		return c.Error(400, fmt.Errorf("invalid item ID"))
	}

	client := dynamodb.NewFromConfig(*globalCfg) // globalCfg initialized safely without user influence
	input := &dynamodb.UpdateItemInput{
		TableName: aws.String("ItemsTable"),
		Key: map[string]aws.AttributeValue{
			"ID": &dynamodb.AttributeValueMemberS{Value: itemID},
		},
		UpdateExpression: aws.String("set #status = :val"),
		ExpressionAttributeNames: map[string]string{
			"#status": "status",
		},
		ExpressionAttributeValues: map[string]aws.AttributeValue{
			":val": &dynamodb.AttributeValueMemberS{Value: "processed"},
		},
	}

	_, err := client.UpdateItem(c.Request().Context(), input)
	if err != nil {
		return c.Error(500, err)
	}
	return c.Render(200, r.JSON(map[string]string{"status": "updated"}))
}

Key remediation practices

• Do not allow user input to override the AWS SDK endpoint or HTTP client transport settings.
• Use AWS SDK’s default credential and endpoint resolution chains; avoid manual endpoint configuration from request parameters.
• Validate and restrict inputs used in DynamoDB key conditions, ensuring they conform to expected patterns and lengths.
• Apply principle of least privilege to the IAM role or user associated with the Buffalo application, limiting permissions to only necessary DynamoDB actions.