Credential Stuffing in Fiber with Api Keys

Credential stuffing is an automated attack technique where previously breached username and password pairs are reused to gain unauthorized access to user accounts. In a Fiber application that relies on API keys for authentication, this risk pattern emerges when API keys are treated as static, long-lived credentials and are not coupled with additional verification or rotation. If an API key is inadvertently exposed—such as being logged, committed to source control, or transmitted over an unencrypted channel—an attacker can use it in a credential stuffing workflow by combining it with known user identifiers or session tokens to replay authenticated requests.

In Fiber, routes are typically defined with middleware that reads an API key from headers, cookies, or query parameters. When these keys are validated without contextual checks—such as scope validation, rate limiting, or binding to a particular client identity—an attacker who possesses a valid key can automate requests across related endpoints, leveraging credential stuffing techniques to escalate abuse. For example, if a key is issued per user but the API does not enforce per-user rate limits or token binding, attackers can parallelize requests using stolen keys to harvest sensitive data or impersonate users across multiple sessions.

The interaction with authentication and authorization checks is critical. If the API key mechanism does not incorporate dynamic elements—such as one-time nonces, rotating secrets, or binding to IP/user-agent fingerprints—keys become reusable credentials that align with the core assumption of credential stuffing: that a valid credential pair can be replayed. Because middleBrick scans API endpoints for authentication weaknesses and BOLA/IDOR risks, it can identify endpoints where API key validation is present but insufficient to prevent replay or credential reuse attacks.

To mitigate credential stuffing risks when using API keys in Fiber, apply defense-in-depth measures: rotate keys regularly, avoid logging them, and bind keys to client context. Below are concrete, syntactically correct examples that demonstrate secure usage patterns.

Example 1: Secure API key validation with context binding

Validate the API key against a stored value and ensure it is used in combination with request metadata such as IP address or user identifier. This reduces the utility of a key captured in a credential stuffing campaign.

const { app, Context } = require("@gofiber/auth");

const validKeys = new Map([
  ["user-123", { key: "ak_live_abc123", ip: "192.0.2.10" }],
  ["user-456", { key: "ak_live_def456", ip: "192.0.2.11" }]
]);

app.use((req, res, next) => {
  const apiKey = req.headers["x-api-key"];
  const clientIp = req.ip;
  const userId = req.headers["x-user-id"];

  if (!apiKey || !userId) {
    return res.status(401).send({ error: "missing_key_or_user" });
  }

  const record = validKeys.get(userId);
  if (!record || record.key !== apiKey || record.ip !== clientIp) {
    return res.status(403).send({ error: "invalid_key_or_context" });
  }

  // Optionally rotate or require re-authentication for sensitive actions
  next();
});

const server = app.listen(3000, () => {
  console.log("Server running on port 3000");
});

Example 2: Key rotation and short-lived tokens

Implement a mechanism to issue short-lived API keys and rotate them periodically. Store hashed versions of keys and validate using a constant-time comparison to avoid timing attacks.

const crypto = require("crypto");
const express = require("express");
const app = express();

// Simulated secure storage: store hashes, not plaintext
const keyStore = new Map(); // key: userId, value: { hash, createdAt }

function hashKey(key) {
  return crypto.createHash("sha256").update(key).digest("hex");
}

function issueKey(userId) {
  const rawKey = crypto.randomBytes(32).toString("hex");
  keyStore.set(userId, { hash: hashKey(rawKey), createdAt: Date.now() });
  return rawKey; // transmit securely to client
}

app.use((req, res, next) => {
  const apiKey = req.headers["x-api-key"];
  const userId = req.headers["x-user-id"];

  if (!apiKey || !userId) {
    return res.status(401).send({ error: "missing_key_or_user" });
  }

  const record = keyStore.get(userId);
  if (!record) {
    return res.status(403).send({ error: "unknown_user" });
  }

  const valid = timingSafeEqual(hashKey(apiKey), record.hash);
  if (!valid) {
    return res.status(403).send({ error: "invalid_key" });
  }

  // Enforce key age policy
  const ageSec = (Date.now() - record.createdAt) / 1000;
  if (ageSec > 86400) { // 24 hours
    return res.status(401).send({ error: "key_expired" });
  }

  next();
});

// Constant-time comparison helper
function timingSafeEqual(a, b) {
  if (a.length !== b.length) return false;
  let result = 0;
  for (let i = 0; i < a.length; i++) {
    result |= a.charCodeAt(i) ^ b.charCodeAt(i);
  }
  return result === 0;
}

app.get("/protected", (req, res) => {
  res.send({ status: "ok" });
});

app.listen(3000, () => console.log("Secure server running"));

These examples emphasize binding keys to context, avoiding static long-lived usage, and incorporating secure comparison and rotation strategies. Combined with middleBrick’s checks for authentication and BOLA/IDOR, these practices reduce the attack surface available for credential stuffing via API keys.