Credential Stuffing in Echo Go with Hmac Signatures
Credential Stuffing in Echo Go with Hmac Signatures — how this specific combination creates or exposes the vulnerability
Credential stuffing is an automated attack where lists of breached username and password pairs are systematically submitted to an endpoint to gain unauthorized access. In Echo Go, when Hmac Signatures are used for request authentication without additional protections, certain implementation patterns can make the API more susceptible to credential stuffing compared to simpler bearer-token approaches.
Echo Go is a framework for building HTTP APIs in Go. When Hmac Signatures are used, the client typically includes an Authorization header with a signature computed over selected headers and a timestamp. If the server validates the signature but does not enforce strict per-request nonce or replay protections and relies only on the signature for authentication, attackers can replay captured requests as part of a credential-stuffing workflow. The attacker iterates over username/password pairs, recomputes the Hmac for each attempt using any non-secret data exposed in headers, and submits the request to the login or token endpoint. Because the signature is derived from headers and a shared secret, the server may accept each forged request as valid if it does not bind the signature tightly to a session or nonce and does not rate-limit authentication attempts.
Another risk arises when the timestamp window is generous or not enforced consistently. A wide allowed clock skew window enables replay of intercepted requests within that window, allowing attackers to automate submission of signed requests at scale. If the endpoint does not track recent nonces or authenticated attempts per user, each signed request appears fresh to the server. Additionally, if error responses differ between a missing signature and an invalid signature, attackers can probe which user accounts exist based on how the API responds to malformed or replayed Hmac-signed requests, facilitating account enumeration alongside credential stuffing.
In an unauthenticated scan context, middleBrick tests how an API behaves when it receives repeated requests with different credentials and signed headers. One of the 12 security checks examines Authentication, looking for weak controls that allow high-volume login attempts without lockouts or CAPTCHAs. When Hmac Signatures are used but the API lacks per-request nonces, replay detection, and rate limiting on authentication endpoints, the scan can identify the endpoint as vulnerable to credential stuffing. Findings include missing nonce enforcement, overly broad timestamp windows, and inconsistent error handling that leaks account existence.
Hmac Signatures-Specific Remediation in Echo Go — concrete code fixes
To harden Echo Go APIs that use Hmac Signatures against credential stuffing, implement strict replay protection, tighter timestamp validation, and robust rate limiting on authentication paths. Below are concrete code examples that demonstrate secure practices.
Example 1: Hmac Signature with nonce and strict timestamp validation
package main
import (
"crypto/hmac"
"crypto/sha256"
"fmt"
"net/http"
"strconv"
"strings"
"time"
"github.com/labstack/echo/v4"
)
const (
// Server-side shared secret stored securely
sharedSecret = "server-side-secret"
// Allowed clock skew in seconds
maxClockSkew = 30
// Store recent nonces per user (in practice use a distributed cache with TTL)
nonceStore = make(map[string]map[string]bool)
)
func isValidTimestamp(ts string) bool {
tsInt, err := strconv.ParseInt(ts, 10, 64)
if err != nil {
return false
}
reqTime := time.Unix(tsInt, 0)
diff := time.Since(reqTime).Abs()
return diff.Seconds() <= maxClockSkew
}
func isReplay(nonce, userID string) bool {
if _, ok := nonceStore[userID]; !ok {
nonceStore[userID] = make(map[string]bool)
}
if nonceStore[userID][nonce] {
return true
}
nonceStore[userID][nonce] = true
// In production, evict old nonces via TTL or background cleanup
return false
}
func computeSignature(method, path, ts, nonce, body string) string {
h := hmac.New(sha256.New, []byte(sharedSecret))
h.Write([]byte(method))
h.Write([]byte(path))
h.Write([]byte(ts))
h.Write([]byte(nonce))
h.Write([]byte(body))
return fmt.Sprintf("%x", h.Sum(nil))
}
func verifySignature(next echo.HandlerFunc) echo.HandlerFunc {
return func(c echo.Context) error {
// Assume these headers are present
auth := c.Request().Header.Get("Authorization")
ts := c.Request().Header.Get("X-Timestamp")
nonce := c.Request().Header.Get("X-Nonce")
providedSig := strings.TrimPrefix(auth, "Hmac ")
if !isValidTimestamp(ts) {
return c.JSON(http.StatusUnauthorized, map[string]string{"error": "invalid_timestamp"})
}
if nonce == "" || ts == "" {
return c.JSON(http.StatusUnauthorized, map[string]string{"error": "missing_headers"})
}
if isReplay(nonce, c.Request().Header.Get("X-User-Id")) {
return c.JSON(http.StatusForbidden, map[string]string{"error": "replay_rejected"})
}
// Compute expected signature on the server side using the request body and headers
bodyBytes, _ := c.Get("requestBody").([]byte) // assume body captured earlier via middleware
expectedSig := computeSignature(c.Request().Method, c.Request().RequestURI, ts, nonce, string(bodyBytes))
if !hmac.Equal([]byte(expectedSig), []byte(providedSig)) {
return c.JSON(http.StatusUnauthorized, map[string]string{"error": "invalid_signature"})
}
return next(c)
}
}
func login(c echo.Context) error {
// Authentication logic here; ensure rate limiting is applied before credential checks
return c.JSON(http.StatusOK, map[string]string{"status": "ok"})
}
func main() {
e := echo.New()
e.POST("/login", verifySignature(login))
e.Start(":8080")
}
Example 2: Enforce rate limiting on authentication endpoints
package main
import (
"net/http"
"time"
"github.com/labstack/echo/v4"
"github.com/labstack/echo/v4/middleware"
)
func main() {
e := echo.New()
// Apply rate limiting specifically to the login route to mitigate credential stuffing
loginThrottle := middleware.RateLimiterWithConfig(middleware.RateLimiterConfig{
Skipper: middleware.DefaultSkipper,
Rate: middleware.Rate{Period: 1 * time.Minute, Burst: 5},
Extractor: func(c echo.Context) (string, error) {
// Key by IP or by user identifier if available after partial auth
return c.Request().RemoteAddr, nil
},
})
e.POST("/login", loginThrottle, func(c echo.Context) error {
// Proceed with Hmac verification and credential validation
return c.JSON(http.StatusOK, map[string]string{"status": "login endpoint with rate limit"})
})
e.Start(":8080")
}
Remediation guidance focuses on binding the Hmac signature to a per-request nonce and a tight timestamp window, rejecting replays, and enforcing rate limits on authentication endpoints. middleBrick’s Authentication check can highlight whether these controls are missing. If you use continuous monitoring, the Pro plan can alert you when authentication endpoints receive high volumes of requests, which may indicate ongoing credential stuffing attempts.