Poodle Attack in Chi with Dynamodb

The Poodle attack (Padding Oracle On Downgraded Legacy Encryption) exploits weak legacy encryption modes and can manifest in API interactions when TLS configurations are misaligned or when applications inadvertently process encrypted data without proper integrity checks. In the context of Chi, a small, expressive routing library for Clojure, a Poodle-related risk arises when an API endpoint built with Chi relies on a backend data store such as DynamoDB and uses encryption or signing mechanisms that are not cryptographically robust.

DynamoDB does not directly implement TLS for data at rest in a way that is exploitable by Poodle; however, the risk emerges when an application layer implemented in Chi performs encryption or signing using a weak cipher (e.g., TLS 1.0/1.1 or a custom cipher with CBC mode and a predictable IV) before storing sensitive payloads in DynamoDB. If the application decrypts or verifies these payloads in a way that leaks information via timing or error messages (a padding oracle), an attacker can iteratively recover plaintext by observing behavioral differences between valid and invalid padding. middleBrick’s system prompt leakage detection and active prompt injection testing would not apply here, but its 12 security checks would flag related findings such as ‘Encryption’ and ‘Input Validation’ when weak cipher usage or inconsistent error handling is detected during an unauthenticated scan of the Chi endpoint.

When scanning a Chi service that stores or retrieves sensitive data from DynamoDB, middleBrick tests whether the API surface exposes unauthenticated endpoints that process encrypted or signed tokens without proper authentication and whether error messages differ based on padding validity. For example, if a Chi route deserializes a JSON Web Encryption (JWE) token and interacts with DynamoDB to retrieve a key or associated metadata, inconsistent handling of decryption failures can create an oracle condition. middleBrick’s ‘Authentication’ and ‘Input Validation’ checks would highlight missing authentication on sensitive routes, while the ‘Encryption’ check would identify weak or missing cipher configurations. Because DynamoDB is often used as a persistence layer for session tokens or user-specific data, an attacker may leverage a Chi endpoint to probe for padding oracle behavior and eventually recover sensitive items stored in DynamoDB.

To mitigate Poodle-like risks in a Chi application that uses DynamoDB, focus on strong cryptographic hygiene, consistent error handling, and authenticated access to DynamoDB. Avoid implementing custom encryption or signing schemes; instead, rely on well-audited libraries and enforce modern TLS for all communications. Ensure that any encryption or signing operations do not reveal padding validity through timing or error messages.

Below are concrete code examples for a Chi application using the AWS SDK for DynamoDB in Clojure. The first example shows how to securely store an encrypted item using envelope encryption with AWS KMS, avoiding custom CBC-mode encryption that could be vulnerable to padding oracles.

(ns myapp.dynamodb
  (:require [aws.sdk.dynamodb :as ddb]
            [aws.sdk.kms :as kms]))

(defn store-sensitive-item [table item]
  (let [kms-key-id "arn:aws:kms:us-east-1:123456789012:key/xxx"
        ;; Use AWS KMS to generate a data key; this avoids managing keys in Chi code
        {:keys [plaintext ciphertext]}
        (kms/generate-data-key kms-key-id {:key-spec "AES_256"})]
    ;; Encrypt sensitive fields locally using the plaintext key, then discard plaintext key
    (let [encrypted-item (update item :ssn #(encrypt-aes-gcm plaintext %))]
      (ddb/put-item table (assoc encrypted-item :encrypted-key ciphertext)))))

(defn retrieve-sensitive-item [table id]
  (let [resp (ddb/get-item table {:key {:id id}})
        item (:Item resp)
        ciphertext (:encrypted-key item)
        {:keys [plaintext]} (kms/decrypt kms-key-id ciphertext)
        ;; Decrypt only after verifying authentication tag; do not reveal padding errors
        decrypted-ssn (decrypt-aes-gcm plaintext (:ssn item))]
    (assoc item :ssn decrypted-ssn)))

This pattern avoids exposing padding-related errors from Chi to the client: errors during decryption should result in a generic failure response rather than detailed messages that could aid an oracle. The second example shows a Chi route that requires authentication before interacting with DynamoDB and returns uniform error responses.

(ns myapp.routes
  (:require [compojure.core :refer [defroutes GET POST]]
            [ring.util.response :as resp]
            [myapp.dynamodb :as db]
            [myapp.auth :refer [current-user]]))

(defroutes api-routes
  (GET "/profile/:id" request
    (if-let [user (current-user request)]
      (try
        (let [item (db/retrieve-sensitive-item :profiles (:id request))]
          (resp/ok item))
        (catch Exception _
          (resp/internal-server-error {:error "Unable to retrieve profile"}))) ; uniform error
      (resp/unauthorized {:error "Unauthorized"}))))

Additionally, enforce TLS 1.2+ for all inbound connections in your Chi server configuration and ensure DynamoDB client connections use HTTPS. middleBrick’s Pro plan includes continuous monitoring and checks against insecure cipher usage across your scanned APIs, which can help detect regressions in cipher or key management practices over time.