Brute Force Attack in Gorilla Mux with Dynamodb

A brute force attack against a Gorilla Mux router backed by DynamoDB can occur when authentication or session enforcement is delegated to the database layer without strict request-rate controls at the HTTP layer. Gorilla Mux is a popular HTTP request router and matcher for Go net/http; it does not provide built-in rate limiting or account lockout. When routes protected by login or token verification are mapped to handlers that query DynamoDB to validate credentials or session state, an attacker can send many rapid requests to the same endpoint.

DynamoDB itself does not throttle per-client IP or API key at the HTTP API gateway level. If your application queries a users table (for example, to fetch a password hash or to check a one-time code) on every authentication attempt and does not enforce server-side rate limiting, the absence of request throttling becomes the weak link. The DynamoDB table may record successful and failed attempts, but without explicit controls the service will continue to process reads and writes, enabling credential spraying or token brute forcing.

This combination also surfaces risks around unauthenticated endpoints. If a route intended for authentication checks mistakenly allows unauthenticated access to DynamoDB-backed handlers, an attacker can probe account existence or infer timing differences by measuring response latency. DynamoDB’s consistent latency can make timing-based detection harder, increasing the likelihood of successful automated guessing. The attack flow commonly involves: (1) identify a login or token verification endpoint, (2) use a list of usernames or identifiers to send rapid requests, and (3) observe whether responses differ for valid versus invalid credentials without triggering safeguards.

Because DynamoDB is often used as a persistent store for identity or session data, findings from a middleBrick scan may highlight missing rate limiting, weak input validation on identifiers, and inconsistent enforcement of authentication across routes. The scanner tests unauthenticated attack surfaces and flags endpoints where brute force could be attempted, especially when combined with weak account lockout policies or missing multi-factor authentication. These checks map to authentication weaknesses in the OWASP API Top 10 and can be surfaced in the dashboard with remediation guidance and compliance mapping to SOC2 and GDPR controls.

To secure a Gorilla Mux application that uses DynamoDB, enforce rate limiting and strict validation before any database call. Implement middleware that tracks attempts per user or IP and short-circuits requests that exceed a threshold. Use DynamoDB conditional writes or transactions to ensure atomic updates for login attempts and lockout state, avoiding race conditions.

Below is a minimal but realistic example in Go using the AWS SDK for DynamoDB. It demonstrates a login handler with per-username rate limiting stored in a separate DynamoDB table, plus secure password verification using a constant-time comparison.

import (
	"context"
	"crypto/subtle"
	"errors"
	"net/http"
	"time"

	"github.com/gorilla/mux"
	"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/aws/aws-sdk-go-v2/service/dynamodb/types"
)

const attemptsTable = "LoginAttempts"
const usersTable = "Users"
const maxAttempts = 5
const lockoutMinutes = 15

var svc = func() *dynamodb.Client {
	cfg, _ := config.LoadDefaultConfig(context.TODO())
	return dynamodb.NewFromConfig(cfg)
}()

func isLockedOut(ctx context.Context, username string) (bool, error) {
	key := map[string]types.AttributeValue{"PK": &types.AttributeValueMemberS{Value: username}}
	out, err := svc.GetItem(ctx, &dynamodb.GetItemInput{
		TableName: aws.String(attemptsTable),
		Key:       key,
	})
	if err != nil || out.Item == nil {
		return false, err
	}
	var ts int64
	if v, ok := out.Item["Timestamp"].(*types.AttributeValueMemberN); ok {
		// parse stored Unix timestamp; omitted for brevity
	}
	if time.Since(time.Unix(ts, 0)) > time.Duration(lockoutMinutes)*time.Minute {
		return false, nil // lockout expired
	}
	var count int64
	if v, ok := out.Item["Count"].(*types.AttributeValueMemberN); ok {
		// parse count; omitted for brevity
	}
	return count >= maxAttempts, nil
}

func recordAttempt(ctx context.Context, username string) error {
	// atomic increment with conditional write to avoid race conditions
	_, err := svc.UpdateItem(ctx, &dynamodb.UpdateItemInput{
		TableName: aws.String(attemptsTable),
		Key: map[string]types.AttributeValue{
			"PK": &types.AttributeValueMemberS{Value: username},
		},
		UpdateExpression:          aws.String("SET #c = if_not_exists(#c, :zero) + :inc"),
		ExpressionAttributeNames:  map[string]string{"#c": "Count"},
		ExpressionAttributeValues: map[string]types.AttributeValue{
			":inc": &types.AttributeValueMemberN{Value: "1"},
			":zero": &types.AttributeValueMemberN{Value: "0"},
		},
		ConditionExpression: aws.String("attribute_not_exists(Timestamp) OR #ts < :cutoff"),
		ExpressionAttributeNames: map[string]string{"#ts": "Timestamp"},
		ExpressionAttributeValues: map[string]types.AttributeValue{
			":cutoff": &types.AttributeValueMemberN{Value: "0"}, // simplified; set to now - lockout window
		},
	})
	return err
}

func loginHandler(w http.ResponseWriter, r *http.Request) {
	username := r.FormValue("username")
	if username == "" {
		http.Error(w, "missing username", http.StatusBadRequest)
		return
	}

	locked, err := isLockedOut(r.Context(), username)
	if err != nil {
		http.Error(w, "server error", http.StatusInternalServerError)
		return
	}
	if locked {
		http.Error(w, "too many attempts, try later", http.StatusTooManyRequests)
		return
	}

	// fetch user record from DynamoDB and verify password hash
	// use constant-time comparison to avoid timing leaks
	storedHash := "..." // retrieve securely
	inputHash := "..."  // derive from request
	if subtle.ConstantTimeCompare([]byte(storedHash), []byte(inputHash)) != 1 {
		recordAttempt(r.Context(), username)
		http.Error(w, "invalid credentials", http.StatusUnauthorized)
		return
	}

	// reset attempts on success
	// ... delete or reset count in DynamoDB
	w.Write([]byte("ok"))
}

func SetupRoutes() *mux.Router {
	r := mux.NewRouter()
	r.HandleFunc("/login", loginHandler).Methods("POST")
	return r
}

In production, pair this with a middleware that enforces global request-rate limits using a token bucket or sliding window stored in a fast in-memory store, and ensure DynamoDB auto scaling is enabled to handle legitimate traffic spikes without degrading protection. middleBrick scans can validate that these controls are present and flag endpoints missing rate limiting or with anomalous timing behavior.