Cryptographic Failures in Buffalo with Bearer Tokens

Cryptographic failures in the Buffalo web framework often intersect with Bearer Token authentication in ways that weaken confidentiality and integrity. When tokens are transmitted over non-TLS channels or stored insecurely, attackers can intercept or guess them. Buffalo applications that skip forced HTTPS or do not set Secure and HttpOnly flags on cookies used to hold session tokens increase the risk of token leakage. Additionally, weak key management for encrypting tokens at rest or using non-constant-time comparison for token validation can lead to bypasses.

In Buffalo, API endpoints that accept Bearer Tokens via the Authorization header must ensure the entire request lifecycle uses TLS. Without enforced HTTPS, tokens can be captured in transit, enabling replay or man-in-the-middle attacks. Even when TLS is used, if the application logs Authorization headers or stores tokens in plaintext in logs, databases, or session stores, it creates a data exposure vector. Cryptographic failures also arise when developers implement custom token encryption instead of relying on battle-tested standards like JWT with strong algorithms (e.g., RS256) and proper key rotation.

Another specific risk involves missing integrity checks. If a Buffalo API issues a Bearer Token without signing it or without validating the token signature on each request, an attacker can tamper with the token payload. For example, changing the role claim from user to admin becomes feasible if the server does not verify the signature. The combination of Buffalo’s convention-based routing and token handling can inadvertently expose endpoints when developers forget to validate token scope or expiration, especially when using opaque tokens without introspection mechanisms.

Real-world attack patterns include token theft via insecure logging (CVE-2021-29451-style log injection) and weak cipher suite negotiation that allows downgrade attacks. The OWASP API Security Top 10 category Cryptographic Failures highlights risks such as unprotected sensitive data in transit and at rest, which map directly to these token handling issues. In Buffalo, ensuring that all routes requiring Bearer Tokens are served over strict HTTPS, using secure cookies for session storage, and validating token signatures with constant-time functions mitigates these cryptographic weaknesses.

Remediation focuses on enforcing transport security, proper token storage, and strict validation. In Buffalo, you can enforce HTTPS globally and protect Bearer Token transmission by configuring your application to redirect HTTP to HTTPS and by setting secure cookie attributes.

First, ensure all API routes that accept Bearer Tokens are served over HTTPS. In your app/controllers/api_controller.ex, you can add a plug that checks for secure connections in production:

defmodule MyAppWeb.Plugs.EnsureHttps do
  import Plug.Conn
  import Phoenix.Controller, only: [redirect: 2]

  def init(opts), do: opts

  def call(conn, _opts) do
    if System.get_env("ENV") == "prod" and not conn.halted do
      if not conn.scheme == :https do
        redirect(conn, [path: "#{conn.request_path}", port: 443], status: 308)
      else
        conn
      end
    else
      conn
    end
  end
end

Second, when storing tokens in cookies (if you use cookie-based sessions), set the Secure and HttpOnly flags in your Buffalo application configuration:

config :my_app, MyAppWeb.Endpoint,
  http: [port: 4000],
  url: [host: "api.example.com", port: 443],
  force_ssl: [hsts: true],
  session_options: [
    store: :cookie,
    key: "_my_app_key",
    secure: true,
    http_only: true,
    same_site: "Lax"
  ]

Third, for Bearer Tokens passed via the Authorization header, validate the token signature using a library like joken and ensure constant-time comparison to prevent timing attacks:

defmodule MyAppWeb.Plugs.Authenticate do
  import Plug.Conn
  import Joken

  def init(opts), do: opts

  def call(conn, _opts) do
    with ["Bearer " << token>>] <- get_req_header(conn, "authorization"),
         {:ok, claims} <- verify_token(token) do
      assign(conn, :current_user, claims["sub"])
    else
      _ -> send_resp(conn, 401, "Unauthorized") >> halt()
    end
  end

  defp verify_token(token) do
    public_key = File.read!("priv/keys/public_key.pem")
    default_claims()
    |> with_claims("iss" == "my-app")
    |> with_claims("exp" >= DateTime.utc_now() |> DateTime.to_unix())
    |> verify("RS256", public_key)
  end
end

Finally, rotate your signing keys regularly and avoid logging Authorization headers. Configure your endpoint to filter sensitive parameters in logs:

config :logger, level: :info
config :my_app, MyAppWeb.Endpoint,
  filter_parameters: ["authorization", "password"]