Beast Attack in Phoenix with Cockroachdb

A Beast Attack in the context of Phoenix with Cockroachdb typically refers to a padding-based attack on cipher block chaining (CBC) mode ciphers, often observed when TLS or application-layer encryption is misconfigured. In this stack, Phoenix applications that rely on Erlang/OTP cryptography libraries to communicate with Cockroachdb may inadvertently use CBC ciphers without proper safeguards. If an attacker can inject or observe ciphertext and supply chosen plaintext, they can iteratively decrypt secure data by observing changes in padding validation errors or timing, especially when endpoints leak information through error messages or inconsistent response times.

When Phoenix endpoints expose raw database errors or structured JSON responses that differ based on padding correctness, the unauthenticated attack surface increases. middleBrick scans this surface and may flag findings related to unauthenticated endpoints and input validation, highlighting scenarios where TLS configurations or cryptographic usage could enable adaptive chosen-ciphertext attacks. For example, an API endpoint that accepts encrypted blobs and passes them to Cockroachdb without authenticated encryption may be vulnerable if the implementation does not verify integrity before decryption.

Consider a Phoenix controller that receives an encrypted parameter and forwards it to Cockroachdb via a direct SQL call:

defmodule MyApp.Repo do
  use Ecto.Repo,
    otp_app: :my_app,
    adapter: Ecto.Adapters.Postgres
end

# This is illustrative; in practice, Cockroachdb uses the PostgreSQL wire protocol.
defmodule MyApp.Crypto do
  @cipher :aes_256_cbc

  def decrypt(ciphertext, key, iv) do
    :crypto.block_decrypt(@cipher, key, iv, ciphertext)
  end
end

# In a controller:
defmodule MyAppWeb.DataController do
  use MyAppWeb, :controller

  def show(conn, %{"token" => token}) do
    key = System.get_env("ENCRYPTION_KEY") |> Base.decode16!()
    iv = String.duplicate("0", 16) |> Base.encode16() |> Base.decode16!()
    plaintext = MyApp.Crypto.decrypt(Base.decode16!(token), key, iv)

    # Forwarding plaintext to Cockroachdb via Ecto (simplified)
    query = from(row in "sensitive_table", where: row.enc_field == ^plaintext)
    results = MyApp.Repo.all(query)

    json(conn, %{data: results})
  end
end

If the decryption fails due to incorrect padding and the error is surfaced as a distinct HTTP 400 versus 401, an attacker can distinguish correct padding and iteratively perform a Beast Attack. middleBrick’s checks for input validation and unauthenticated endpoints would highlight this controller as a risk, especially if the endpoint does not enforce authentication or if TLS CBC ciphers are in use without AEAD alternatives.

Remediation focuses on using authenticated encryption, avoiding raw CBC where possible, and ensuring errors do not leak padding validity. In Phoenix, prefer AES-GCM or ChaCha20-Poly1305 via Plug.Crypto or Guardian for token handling, and ensure database interactions via Ecto do not expose low-level crypto to user input.

Instead of manually decrypting before querying, perform decryption only after validating authenticity, and use parameterized queries to avoid injection. Below is a revised approach using authenticated encryption and safe parameter handling:

defmodule MyApp.Crypto do
  @aead_cipher :aes_256_gcm

  def encrypt(plaintext, key) do
    iv = :crypto.strong_rand_bytes(12)
    {ciphertext, auth_tag} = :crypto.block_encrypt(@aead_cipher, key, iv, plaintext)
    {iv, ciphertext, auth_tag}
  end

  def decrypt(nil, _key), do: {:error, :invalid_token}
  def decrypt({iv, ciphertext, auth_tag}, key) do
    :crypto.block_decrypt(@aead_cipher, key, iv, ciphertext, auth_tag)
  end
end

defmodule MyAppWeb.DataController do
  use MyAppWeb, :controller

  def show(conn, %{"token" => token_b64}) do
    case Base.decode64(token_b64) do
      {:ok, token} ->
        key = System.get_env("ENCRYPTION_KEY") |> Base.decode64!()
        case MyApp.Crypto.decrypt(token, key) do
          {:ok, plaintext} ->
            # Use plaintext as a parameterized query value; no raw SQL concatenation
            query = from(row in "sensitive_table", where: row.enc_field == ^plaintext)
            results = MyApp.Repo.all(query)
            json(conn, %{data: results})

          {:error, :invalid_token} ->
            conn
            |> put_status(:bad_request)
            |> json(%{error: "invalid token"})
        end

      _ ->
        conn
        |> put_status(:bad_request)
        |> json(%{error: "malformed token"})
    end
  end
end

Additionally, enforce TLS with AEAD ciphers (e.g., TLS_AES_256_GCM_SHA384) in your endpoint configuration and avoid exposing stack traces or detailed error messages that could aid an attacker. middleBrick’s scans for data exposure, encryption, and input validation will help identify whether your endpoints inadvertently disclose cryptographic behavior or weak configurations.