Sql Injection in Chi with Dynamodb

SQL Injection is commonly associated with relational databases, but injection-style attacks can also manifest against NoSQL databases such as DynamoDB when query construction is driven by untrusted input. In a Chi application, this risk arises when developers build query expressions—such as KeyConditionExpressions, FilterExpressions, or projection logic—by string concatenation or interpolation using user-controlled data. Because DynamoDB APIs accept expression strings and attribute values separately, failing to isolate user input into expression attribute values enables attackers to manipulate the structure of the request.

Chi is a lightweight routing library for Clojure that typically does not provide built-in data access safeguards; therefore, responsibility falls on the developer to avoid embedding raw input into DynamoDB API calls. For example, concatenating a table name or key attribute name from request parameters can lead to schema manipulation or traversal across partitions. Similarly, injecting logical operators like OR or AND into expression values (if values are mistakenly placed into expression strings rather than bound as attribute values) can alter filter logic and bypass intended access controls.

An attacker may probe endpoints that expose DynamoDB-backed resources by injecting crafted payloads such as id = '123' OR begins_with(pk, '') into a query parameter that is directly interpolated into a KeyConditionExpression. If the application does not validate or parameterize the input, this can change the partition key condition in unintended ways, potentially returning multiple items or revealing data belonging to other users. In a serverless or microservice context, these queries often run with elevated IAM permissions, increasing the impact of unauthorized data access.

Beyond read operations, injection can affect write and update paths. For instance, using user input to construct an UpdateExpression without isolating attribute names and values can overwrite critical attributes or introduce unexpected condition checks that bypass optimistic concurrency controls. Because DynamoDB does not offer SQL-style prepared statements, the onus is on the developer to strictly separate expression structure from data.

Remediation centers on strict separation of expression structure from data, using DynamoDB’s expression attribute names and expression attribute values correctly, and avoiding string interpolation for query construction. In Chi, this means ensuring that any user input is treated strictly as a value bound via the :values style map, while table names, attribute names, and expression templates are defined server-side or validated against a strict allowlist.

Below is a secure example using the official AWS SDK for Clojure (via integrant or similar) that demonstrates parameterized DynamoDB queries in a Chi handler. The key is to never embed request parameters directly into expression strings.

(ns app.handler
  (:require [aws.sdk.dynamodb :as ddb]))

(defn get-user-by-id [table-name user-id]
  (let [params {:table-name table-name
                :key-condition-expression "pk = :uid"
                :expression-attribute-names {"#pk" "pk"}
                :expression-attribute-values {":uid" {:s user-id}}}]
    (ddb/query params)))

(defn app [request]
  (let [table-name "myapp-users"
        user-id (get-in request [:params :id])]
    (if (some? user-id)
      (get-user-by-id table-name user-id)
      {:status 400 :body "missing id"})))

For update operations, apply the same discipline. Use expression attribute names for any attribute that might be user-supplied (to prevent reserved-word injection or path traversal), and expression attribute values for data values. Avoid building condition expressions by concatenating strings that include raw input.

(defn update-user-email [table-name user-id new-email]
  (let [params {:table-name table-name
                :key {:pk {:s user-id}}
                :update-expression "SET #em = :e"
                :condition-expression "attribute_exists(#em)"
                :expression-attribute-names {"#em" "email"}
                :expression-attribute-values {":e" {:s new-email}}}]
    (ddb/update-item params)))

(defn put-handler [request]
  (let [table-name "myapp-users"
        user-id (get-in request [:params :id])
        new-email (get-in request [:params :email])]
    (if (and user-id new-email)
      (update-user-email table-name user-id new-email)
      {:status 400 :body "missing fields"})))

Additionally, validate and normalize input before using it as an expression attribute value. While DynamoDB’s type system protects against some injection forms, logical operators should not be introduced via concatenated strings. Leverage middleware in Chi to sanitize and constrain parameters, and prefer allowlists for table or index names rather than dynamic references.

For broader protection, use the middleBrick CLI to scan endpoints built on DynamoDB-backed APIs. Run middlebrick scan <url> to detect injection-prone patterns in unauthenticated attack surfaces and integrate the GitHub Action to fail builds when risk scores degrade. The Pro plan supports continuous monitoring to catch regressions early, and the MCP Server enables on-the-fly checks from your IDE while you develop Chi handlers.