Phishing Api Keys in Echo Go with Hmac Signatures

In Echo Go, using HMAC signatures to protect API keys can inadvertently create a phishing-friendly surface if the key or the signing logic is exposed to untrusted outputs. When an API key is transmitted or logged in a way that can be intercepted or reflected, an attacker can capture the key and reuse it to forge valid HMAC-signed requests. Echo Go applications that embed the key in query parameters, response bodies, or error messages increase the risk of phishing, because the key can be exfiltrated and used elsewhere.

HMAC relies on a shared secret; if that secret is phished, an attacker can generate valid signatures for arbitrary inputs. In Echo Go, if routes that accept signed requests do not strictly validate the origin and do not enforce strict referer or origin checks, a malicious site can trick a user’s browser into making signed requests that the server accepts as legitimate. This is especially dangerous when the signing process does not include a per-request nonce or timestamp, allowing replay attacks where captured signed requests are reused.

Additionally, if the server returns sensitive data in responses that are cached or logged, the HMAC signature and related metadata can be exposed. An attacker who gains access to logs or cached responses might extract enough information to perform offline brute-force or guessing attacks on the API key, particularly if the key has low entropy or is reused across multiple endpoints. Echo Go handlers that do not differentiate between public and sensitive endpoints in their routing can unintentionally expose signing material through seemingly innocuous routes.

The interplay between Echo Go’s routing flexibility and HMAC signature verification means that developers must ensure that keys are never transmitted in URLs, are stored securely, and are never logged. MiddleBrick’s scans can detect endpoints that leak keys in responses or that accept requests with weak or missing signature validation, highlighting places where phishing could be leveraged against the HMAC scheme.

For example, a vulnerable Echo Go route might look like this, where the API key is handled insecurely:

// Vulnerable: key passed in query and logged
func KeyHandler(c echo.Context) error {
    apiKey := c.QueryParam("key")
    signature := c.QueryParam("signature")
    // Log raw key — risk of exposure in logs
    log.Printf("Received key: %s", apiKey)
    if !verifyHMAC(apiKey, c.Request().Body, signature) {
        return echo.NewHTTPError(http.StatusUnauthorized, "invalid signature")
    }
    return c.String(http.StatusOK, "ok")
}

func verifyHMAC(key string, body io.Reader, signature string) bool {
    secret := []byte(key) // key used directly as secret
    hasher := hmac.New(sha256.New, secret)
    buf := new(bytes.Buffer)
    buf.ReadFrom(body)
    hasher.Write(buf.Bytes())
    expected := hex.EncodeToString(hmac.Sum256(secret, hasher.Sum(nil)))
    return hmac.Equal([]byte(expected), []byte(signature))
}

This pattern exposes the key via query strings and logs, making it susceptible to phishing and replay. An attacker can capture the key and signature from logs or network traces and use them to impersonate legitimate clients.

To secure HMAC signatures in Echo Go, keep the API key out of HTTP traffic and logs, use cryptographically random secrets, and ensure strict verification that includes context like method, path, and a nonce or timestamp. Store the key in environment variables or a secure secret manager, and access it only during server initialization. Never concatenate or log the key in any user-facing output.

Use a constant-time comparison for signatures and include additional binding data such as the request method and a timestamp to prevent replay. Below is a secure pattern for generating and verifying HMAC signatures in Echo Go:

// Secure: key from environment, no logging, timestamp binding
import (
    "crypto/hmac"
    "crypto/sha256"
    "encoding/hex"
    "os"
    "strconv"
    "time"
)

var apiSecret []byte

func init() {
    secret := os.Getenv("API_HMAC_SECRET")
    if secret == "" {
        // fail closed in production; handle appropriately
        panic("API_HMAC_SECRET not set")
    }
    apiSecret = []byte(secret)
}

func generateHMAC(payload []byte, timestamp int64) string {
    mac := hmac.New(sha256.New, apiSecret)
    mac.Write(payload)
    mac.Write([]byte(strconv.FormatInt(timestamp, 10)))
    return hex.EncodeToString(mac.Sum(nil))
}

func SecureHandler(c echo.Context) error {
    body, err := io.ReadAll(c.Request().Body)
    if err != nil {
        return echo.NewHTTPError(http.StatusBadRequest, "invalid body")
    }
    // Restore body for further use if needed
    c.Request().Body = io.NopCloser(bytes.NewReader(body))

    timestampStr := c.Request().Header.Get("X-Timestamp")
    timestamp, err := strconv.ParseInt(timestampStr, 10, 64)
    if err != nil || time.Since(time.Unix(timestamp, 0)) > 5*time.Minute {
        return echo.NewHTTPError(http.StatusBadRequest, "invalid timestamp")
    }

    receivedSig := c.Request().Header.Get("X-Signature")
    expected := generateHMAC(body, timestamp)
    if !hmac.Equal([]byte(expected), []byte(receivedSig)) {
        return echo.NewHTTPError(http.StatusUnauthorized, "invalid signature")
    }
    return c.String(http.StatusOK, "authenticated")
}

func generateClientRequest(url string, body []byte) (string, string, int64, error) {
    timestamp := time.Now().Unix()
    mac := hmac.New(sha256.New, apiSecret)
    mac.Write(body)
    mac.Write([]byte(strconv.FormatInt(timestamp, 10)))
    signature := hex.EncodeToString(mac.Sum(nil))
    return url, signature, timestamp, nil
}

// Example usage of client request generation
// clientURL, clientSig, ts, _ := generateClientRequest("https://api.example.com/endpoint", payload)
// req.Header.Set("X-Signature", clientSig)
// req.Header.Set("X-Timestamp", strconv.FormatInt(ts, 10))

Key improvements include loading the secret from environment variables at startup, binding the signature to a timestamp to mitigate replay, using hmac.Equal for constant-time comparison, and avoiding any logging of the secret. This reduces the risk that a captured signature or key can be used in phishing or replay attacks.

When integrating with CI/CD or using the middleBrick CLI (middlebrick scan <url>) or GitHub Action, ensure that the scan configuration flags sensitive endpoints so that findings related to key exposure are prioritized. The dashboard can help track whether HMAC-related misconfigurations persist across deployments.