Command Injection in Chi with Dynamodb

Command Injection occurs when an attacker can inject and execute arbitrary system commands through an application. In a Chi application using Dynamodb, this typically arises when input from HTTP requests is passed to system-level commands that interact with or are influenced by Dynamodb operations, such as invoking the AWS CLI or SDK utilities via unsafe string interpolation.

Chi is a minimalistic Clojure web framework that encourages explicit routing and parameter handling. When developers use unchecked or loosely validated parameters to construct shell commands—especially in administrative or debugging endpoints—the application becomes vulnerable. For example, a route that accepts a table_name or key parameter and passes it directly to a shell command like aws dynamodb describe-table creates an injection vector.

The combination is risky because Dynamodb operations often require precise attribute values, and attackers can exploit command injection to manipulate or extract sensitive data by injecting malicious flags or secondary commands. A typical vulnerable pattern in Chi might look like concatenating user input into a shell command string without sanitization, bypassing intended access controls around Dynamodb resources.

Because middleBrick scans the unauthenticated attack surface, it can detect such command injection risks by analyzing endpoint behavior and input handling patterns, even when the endpoint interacts with Dynamodb. This helps identify insecure integrations before they are exploited in the wild.

To remediate command injection in Chi when working with Dynamodb, avoid constructing shell commands with user input. Instead, use the AWS SDK for Clojure or Java interop to call Dynamodb APIs directly, which eliminates shell injection risks entirely.

Below is a safe, idiomatic approach using the official AWS SDK for Java, invoked via Clojure interop. This example retrieves a table description without invoking a shell:

(ns myapp.dynamodb
  (:import [software.amazon.awssdk.services.dynamodb DynamoDbClient]
           [software.amazon.awssdk.services.dynamodb.model DescribeTableRequest DescribeTableResponse]))

(defn make-client []
  (DynamDbClient/create))

(defn describe-table [table-name]
  (let [client (make-client)
        request (DescribeTableRequest. (doto (DescribeTableRequest$Builder.)
                                         (.tableName table-name)))]
    (.describeTable client request)))

If you must invoke system utilities for legacy reasons, rigorously validate and sanitize inputs, and avoid direct interpolation. For instance, use a whitelist of allowed table names and pass arguments as a vector to process to prevent shell parsing:

(def allowed-tables #{"users" "orders" "products"})

(defn safe-describe [table-name]
  (when (allowed-tables table-name)
    (let [cmd ["aws" "dynamodb" "describe-table" "--table-name" table-name]
          result (-> (clojure.java.shell/sh cmd)
                     :out)]
      (println result))))

Additionally, enforce strict input validation at the Chi route level. Use middleware to reject or coerce unexpected characters and enforce schema constraints. middleBrick can help identify such injection paths during scans by correlating endpoint definitions with runtime behavior, supporting compliance mappings to OWASP API Top 10 and other frameworks.

For teams using the middleBrick ecosystem, the CLI (middlebrick scan <url>) and GitHub Action can integrate these checks into development workflows, while the Web Dashboard provides ongoing tracking of security scores. The MCP Server enables AI coding assistants to surface risks during implementation, promoting secure patterns proactively.