Credential Stuffing in Buffalo with Jwt Tokens

Credential stuffing is an automated attack where attackers use lists of breached username and password pairs to gain unauthorized access. When an API endpoint in Buffalo uses JWT tokens for authentication without adequate protections, the framework can inadvertently support or fail to mitigate this style of attack. In Buffalo, typical authentication flow involves verifying user credentials and then generating a signed JWT token that the client includes in subsequent requests via the Authorization header as a Bearer token. If the application does not enforce rate limiting on the login endpoint and does not validate the strength of credentials, attackers can rapidly submit many combinations, and successful logins will return a valid JWT token.

The vulnerability arises because JWT tokens, once issued, are often accepted without additional checks on each request. In Buffalo, when you use the built-in JSON parsing and session management, it is easy to configure routes that issue a JWT token after a simple password match without multi-factor authentication or suspicious request analysis. Attackers rely on predictable token issuance and the absence of per-user or per-IP rate controls. They may also exploit weak token signing keys, predictable secrets, or missing token binding, which allows them to reuse intercepted tokens across sessions. The framework does not inherently prevent these patterns; developers must explicitly add protections such as token expiration, revocation lists, and binding claims to client fingerprints to reduce the impact of credential stuffing.

Additionally, Buffalo applications that rely on JWT tokens stored in cookies without the HttpOnly and Secure flags, or that do not implement proper SameSite attributes, can expose tokens to theft via cross-site scripting, which compounds the risk of automated credential validation. Because JWT tokens often carry identity claims, once an attacker obtains a valid token through credential stuffing or other means, they can impersonate users until the token expires or is revoked. Therefore, the combination of Buffalo’s convention-driven authentication scaffolding and JWT token usage requires careful hardening to ensure that token issuance is tightly coupled with robust authentication controls and continuous monitoring.

To remediate credential stuffing risks specific to JWT tokens in Buffalo, implement strict rate limiting on authentication endpoints, enforce strong password policies, and bind tokens to client context. Below are concrete code examples that demonstrate secure practices.

Rate limiting on login route

Use a plug to limit login attempts per IP or per user identifier before issuing a JWT token:

defmodule MyAppWeb.RateLimiter do
  @max_attempts 5
  @ttl 60_000 # milliseconds

  def init(opts), do: opts

  def call(conn, _opts) do
    case get_session(conn, :login_attempts) do
      nil -> conn
      count when count >= @max_attempts ->
        conn
        |> put_status(429)
        |> json(%{error: "Too many attempts. Try again later."})
        |> halt()
      _ -> conn
    end
  end
end

Secure JWT generation and validation

Generate tokens with a strong secret, short expiration, and claims that include issuer and audience:

token =
  Joken.encode_and_sign(
    %{
      sub: user.id,
      iss: "myapp",
      aud: "myapp-users",
      exp: DateTime.utc_now() |> DateTime.add(15, :minute) |> DateTime.to_unix()
    },
    "HS256",
    "your_strong_secret_here"
  )

Validate the token on each authenticated request by checking expiration, issuer, and audience:

case Joken.decode_and_verify(token, "your_strong_secret_here", [verification: [iss: "myapp", aud: "myapp-users"]]) do
  {:ok, claims} -> assign(conn, :current_user_id, claims["sub"])
  {:error, _reason} -> conn |> put_status(401) |> json(%{error: "Unauthorized"}) |> halt()
end

Binding tokens to client context

Include a fingerprint derived from headers or IP to make token replay harder:

fingerprint =
  :crypto.hash(:sha256, conn.remote_ip |> Tuple.to_list() |> Enum.join(".") <> req_headers["user-agent"])
  |> Base.url_encode64(padding: false)

claims = %{
  sub: user.id,
  jti: UUID.uuid4(),
  fingerprint: fingerprint
}

On validation, compare the incoming fingerprint claim with the current request fingerprint to reject mismatches.

Cookie settings for JWT storage

If storing JWT in cookies, set secure attributes:

resp(conn, :ok)
|> put_resp_cookie("access_token", token,
  http_only: true,
  secure: true,
  same_site: "Lax",
  max_age: 900
)