Format String in Adonisjs with Dynamodb

Format string vulnerabilities occur when user-controlled input is passed directly into a function that interprets format specifiers (e.g., %s, %d, %n) without proper sanitization. In AdonisJS, this commonly arises when developers use Node-style string formatting utilities or logging libraries that accept format strings. When combined with DynamoDB operations—such as constructing table names, key conditions, or filter expressions from user input—the risk emerges if formatted strings include unchecked external data.

Consider an endpoint that retrieves a DynamoDB table name from request parameters and uses it in a formatted log message or query builder helper. If the table name or a query parameter is directly interpolated using a format string function (e.g., util.format(userInput)), an attacker can inject format specifiers. This may lead to information disclosure through irregular memory reads (e.g., %p), denial-of-service via excessive resource consumption (e.g., %n causing write operations), or in rare runtime environments, arbitrary code execution depending on linked native modules. In AdonisJS, which often uses JavaScript utility libraries for data formatting, passing unsanitized request inputs into format functions before DynamoDB serialization creates an implicit injection surface.

DynamoDB-specific exposure occurs when formatted strings influence low-level SDK calls. For example, if a format string is used to construct a KeyConditionExpression or FilterExpression, injected format specifiers could corrupt expression syntax, leading to unexpected query behavior or exposure of unintended item attributes during scan operations. While DynamoDB itself does not interpret format specifiers, the surrounding AdonisJS logic that builds these expressions does. An attacker might leverage format string specifiers to manipulate logging verbosity, trigger error paths that reveal stack traces, or indirectly probe internal memory layouts through crafted payloads. The interplay between AdonisJS’s request lifecycle and DynamoDB’s strict attribute-value protocol amplifies the impact when format strings are used to transform inputs before SDK serialization.

To illustrate, an unsafe implementation might look like this:

const util = require('node:util');
const { DynamoDB } = require('aws-sdk');
const dynamo = new DynamoDB();

async function unsafeQuery(tableName, userId) {
  const formattedTable = util.format(tableName); // User-controlled tableName
  const params = {
    TableName: formattedTable,
    KeyConditionExpression: util.format('user_id = :uid', { uid: userId })
  };
  return dynamo.query(params).promise();
}

Here, tableName and format arguments are directly influenced by external input. If an attacker sends tableName as '%s %n', it could distort logging or memory behavior in the AdonisJS layer before the request reaches DynamoDB. The fix is to avoid format-string functions for external data and use parameterized construction or strict validation instead.

Remediation focuses on eliminating format string usage when handling DynamoDB-related inputs in AdonisJS. Never pass request-derived data directly into format specifier functions. Instead, use explicit string concatenation, template literals with strict validation, or dedicated SDK parameter builders. Validate table names against an allowlist or regex pattern that permits only alphanumeric characters and underscores, and reject any input containing format specifiers like %.

Below are concrete, safe implementations for AdonisJS applications interacting with DynamoDB.

Safe Table Name Handling

Validate and use table names without formatting functions:

const { DynamoDB } = require('aws-sdk');
const dynamo = new DynamoDB();

function isValidTableName(name) {
  return /^[a-zA-Z0-9_]+$/.test(name);
}

async function safeQuery(tableName, userId) {
  if (!isValidTableName(tableName)) {
    throw new Error('Invalid table name');
  }
  const params = {
    TableName: tableName, // Direct use, no formatting
    KeyConditionExpression: 'user_id = :uid',
    ExpressionAttributeValues: { ':uid': { S: userId } }
  };
  return dynamo.query(params).promise();
}

Safe Expression Building

Construct DynamoDB expressions using parameterized values, not format strings:

async function buildFilter(filters) {
  let filterExpression = '';
  const expressionValues = {};
  const keys = Object.keys(filters);
  
  keys.forEach((key, index) => {
    const placeholder = `#val${index}`;
    const valuePlaceholder = `:val${index}`;
    if (index > 0) filterExpression += ' AND ';
    filterExpression += `${key} = ${valuePlaceholder}`;
    expressionValues[placeholder] = { S: key };
    expressionValues[valuePlaceholder] = { S: filters[key] };
  });
  
  return { FilterExpression: filterExpression, ExpressionAttributeValues: expressionValues };
}

// Usage within AdonisJS controller
const filterParams = buildFilter({ status: 'active', role: 'admin' });
const params = {
  TableName: 'Users',
  FilterExpression: filterParams.FilterExpression,
  ExpressionAttributeValues: filterParams.ExpressionAttributeValues
};

Logging Without Format Strings

Use simple concatenation or structured logging that does not interpret specifiers:

const logger = use('Logger');

function auditLog(tableName, action) {
  // Safe: direct string construction
  logger.info(`Action: ${action}, Table: ${tableName}`);
}

By adopting these patterns, AdonisJS applications avoid format string injection when working with DynamoDB. The key is to treat all external inputs as opaque values, validate them strictly, and rely on the DynamoDB SDK’s native parameterization rather than runtime string formatting.