Brute Force Attack in Echo Go with Dynamodb

A brute force attack against an API built with Echo Go and using DynamoDB as the backend typically exploits weak authentication or enumeration-prone endpoints. In this stack, the vulnerability often arises when login or lookup endpoints do not enforce adequate rate limiting or consistent response behavior. For example, an endpoint like /login or /users/{username} may return different HTTP status codes or response times depending on whether the username exists in DynamoDB. This difference allows an attacker to enumerate valid usernames without authentication, narrowing the search space for credential guessing.

Echo Go applications that interact with DynamoDB may inadvertently expose timing differences. A query against DynamoDB for a non-existent user might complete faster than a query for an existing user due to index behavior or item size. An attacker can measure response times to infer valid usernames, then attempt password brute forcing only against discovered accounts. Without proper rate limiting or account lockout mechanisms, each password attempt becomes a discrete request that can be retried indefinitely or across distributed IPs.

The combination of Echo Go’s flexible routing and DynamoDB’s key-based access patterns can also lead to insecure direct object references (BOLA/IDOR) when object keys are derived from user-controlled input like usernames. If an endpoint such as /api/profile/{username} uses the username directly to construct a DynamoDB key without verifying the requesting user’s permissions, an authenticated brute force becomes a horizontal privilege escalation. The attacker iterates through known or guessed usernames and retrieves profiles they should not access.

Because middleBrick scans the unauthenticated attack surface, it can detect whether your Echo Go + DynamoDB API reveals username enumeration via inconsistent status codes or timing, and whether rate limiting is absent or easily bypassed. Findings will map to the Authentication and BOLA/IDOR checks, highlighting the risk and providing remediation guidance aligned with OWASP API Top 10 and related compliance frameworks.

To secure an Echo Go API that uses DynamoDB, ensure authentication is required before any user lookup, standardize response times and messages, and enforce strict rate limiting. Below are concrete code examples that address enumeration and brute force risks.

1. Constant-time response for user existence checks

Avoid leaking username validity through timing differences. Use a dummy query or constant-time logic when a username is not found.

package main

import (
    "context"
    "net/http"
    "time"

    "github.com/labstack/echo/v4"
    "github.com/aws/aws-sdk-go-v2/aws"
    "github.com/aws/aws-sdk-go-v2/service/dynamodb"
    "github.com/aws/aws-sdk-go-v2/service/dynamodb/types"
)

// dummyKey is a pre-provisioned item used to ensure consistent latency.
const dummyKey = "dummy_user_placeholder"

func checkUserExists(ctx context.Context, svc *dynamodb.Client, username string) (bool, error) {
    // Always perform a real lookup.
    out, err := svc.GetItem(ctx, &dynamodb.GetItemInput{
        Key: map[string]types.AttributeValue{
            "username": &types.AttributeValueMemberS{Value: username},
        },
        TableName: aws.String("users"),
    })
    if err != nil {
        return false, err
    }
    if out.Item == nil {
        // Fall back to dummy lookup to consume similar time.
        _, _ = svc.GetItem(ctx, &dynamodb.GetItemInput{
            Key: map[string]types.AttributeValue{
                "username": &types.AttributeValueMemberS{Value: dummyKey},
            },
            TableName: aws.String("users"),
        })
        return false, nil
    }
    return true, nil
}

func loginHandler(c echo.Context) error {
    username := c.FormValue("username")
    password := c.FormValue("password")

    exists, err := checkUserExists(c.Request().Context(), svc)
    if err != nil {
        return c.JSON(http.StatusInternalServerError, map[string]string{"error": "internal error"})
    }

    // Always perform a slow, constant-time password verification when username not found.
    dummyHash := bcryptHash("dummy")
    bcryptCompare(dummyHash, password)

    if !exists {
        return c.JSON(http.StatusUnauthorized, map[string]string{"error": "invalid credentials"})
    }

    // Proceed with real password verification...
    return c.JSON(http.StatusOK, map[string]string{"status": "ok"})
}

2. Enforce rate limiting at the Echo middleware level

Use a shared store (e.g., Redis) to limit attempts per username or IP, and apply a fixed delay to prevent rapid guessing.

import (
    "github.com/labstack/echo/v4/middleware"
    "github.com/go-redis/redis/v8"
)

func setupRateLimiter(e *echo.Echo, rdb *redis.Client) {
    e.Pre(middleware.RateLimiterWithConfig(middleware.RateLimiterConfig{
        Store: middleware.NewRedisRateLimiter(rdb).Get, // implement Get/Set per key
        Skipper: middleware.DefaultSkipper,
        Rate: middleware.Rate{},
        IdentifierExtractor: func(c echo.Context) (string, error) {
            // Combine IP and username to limit per user/IP pair.
            username := c.FormValue("username")
            ip := c.RealIP()
            if username != "" {
                return ip + ":" + username, nil
            }
            return ip, nil
        },
        OnLimitReached: func(next echo.HandlerFunc) echo.HandlerFunc {
            return func(c echo.Context) error {
                return c.JSON(http.StatusTooManyRequests, map[string]string{"error": "too many requests"})
            }
        },
    }))
}

3. Require authentication for profile endpoints and validate ownership

Ensure that any DynamoDB key construction includes ownership checks so that brute forcing one profile does not expose others.

func getProfileHandler(c echo.Context) error {
    userID, ok := c.Get("user_id").(string)
    if !ok {
        return c.JSON(http.StatusUnauthorized, map[string]string{"error": "unauthorized"})
    }
    requestedUser := c.Param("username")
    // Map username to userID securely (e.g., via a lookup table) and compare.
    if !ownsProfile(userID, requestedUser) {
        return c.JSON(http.StatusForbidden, map[string]string{"error": "forbidden"})
    }

    out, err := svc.GetItem(c.Request().Context(), &dynamodb.GetItemInput{
        Key: map[string]types.AttributeValue{
            "username": &types.AttributeValueMemberS{Value: requestedUser},
        },
        TableName: aws.String("users"),
    })
    if err != nil || out.Item == nil {
        return c.JSON(http.StatusNotFound, map[string]string{"error": "not found"})
    }
    return c.JSON(http.StatusOK, out.Item)
}

4. Use AWS SDK best practices and defensive settings

Configure DynamoDB client timeouts and retries to avoid serving slow responses that aid timing attacks. Also prefer parameterized queries over constructing keys from raw user input.

cfg := aws.Config{
    Region: aws.String("us-east-1"),
    // Set reasonable timeouts to bound request duration.
    HTTPClient: http.Client{
        Timeout: 5 * time.Second,
    },
}
svc := dynamodb.NewFromConfig(cfg)