Out Of Bounds Read in Adonisjs with Dynamodb

An Out Of Bounds Read occurs when an application reads from memory locations outside the intended buffer or data structure. In AdonisJS applications that use DynamoDB as a persistence layer, this typically arises from unchecked index or key values used when constructing requests to DynamoDB or when processing query results. Because AdonisJS is a Node.js framework, JavaScript runtime behavior and the AWS SDK for JavaScript drive interactions with DynamoDB, and insecure handling of user-supplied identifiers can lead to reads beyond expected result sets or misaligned array accesses derived from DynamoDB responses.

Consider a route that retrieves a user’s profile by numeric user ID supplied in the URL, then uses that ID to index into a permissions array derived from a DynamoDB item. If the ID is not validated and is used directly as an array index, an out-of-bounds read can occur when the ID exceeds the array length. For example:

// routes files.js
Route.get('files/:id', async ({ params }) => {
  const { id } = params;
  // Assume getFileRecord returns an item with an array of tags from DynamoDB
  const file = await FileService.getFileRecord(id);
  // Vulnerable: using user-controlled `tagIndex` directly as array index
  const tagIndex = Number(request.input('tagIndex'));
  const tag = file.tags[tagIndex]; // Out Of Bounds Read if tagIndex >= file.tags.length
  return { tag };
});

DynamoDB itself does not impose index boundaries in the same way an array does, but the application layer constructs arrays from DynamoDB query results (for example, a list of sort keys or a mapped attribute). If the application does not validate that an index falls within the bounds of that array, the JavaScript engine may read undefined or adjacent memory-like representations, potentially exposing sensitive data or causing unstable behavior. This is especially relevant when the query returns a sparse set of attributes or when the client controls pagination parameters such as Limit or ExclusiveStartKey, which can shift which items are returned and affect how results are materialized into arrays.

Another scenario involves scanning or querying DynamoDB with a FilterExpression that references a numeric attribute derived from user input. If the attribute is used to compute offsets or slices on the client side without range checks, the resulting slice indices can fall outside valid bounds. For instance, using request query parameters to skip or limit items without validating against the actual result set size can produce misaligned reads when the client attempts to access a specific position in a derived list.

AdonisJS middleware and route handlers must treat all external inputs as untrusted. This includes path parameters, query strings, and JSON payloads. When combined with DynamoDB’s flexible schema, where attributes may be missing or of varying types, the risk of processing invalid indices increases. Proper validation, schema enforcement, and defensive coding are essential to prevent out-of-bounds reads that could leak unintended data or destabilize service behavior.

Remediation centers on strict validation of indices and bounds before using values to index into arrays derived from DynamoDB results. Always verify that numeric indices are integers, non-negative, and strictly less than the array length. Use helper functions to sanitize user input and avoid direct indexing with raw request data.

Below is a secure pattern for retrieving a file and safely accessing a tag by index, using AdonisJS services and the AWS SDK for JavaScript (v3) with DynamoDB:

// services/FileService.js
const { DynamoDBClient, GetItemCommand } = require('@aws-sdk/client-dynamodb');
const client = new DynamoDBClient({ region: 'us-east-1' });

class FileService {
  static async getFileRecord(id) {
    const command = new GetItemCommand({
      TableName: 'Files',
      Key: { id: { N: String(id) } }
    });
    const response = await client.send(command);
    return response.Item ? this.mapItem(response.Item) : null;
  }

  static mapItem(item) => ({
    id: item.id.N,
    tags: item.tags?.L?.map(el => el.S) || []
  });
}

module.exports = FileService;

And a revised route that validates the tag index before accessing the array:

// routes files.js
Route.get('files/:id', async ({ request, response }) => {
  const { id } = request.get();
  const file = await FileService.getFileRecord(id);
  if (!file) {
    return response.status(404).send({ error: 'Not found' });
  }

  const tagIndex = Number(request.input('tagIndex'));
  // Validate index bounds explicitly
  if (!Number.isInteger(tagIndex) || tagIndex < 0 || tagIndex >= file.tags.length) {
    return response.status(400).send({ error: 'Invalid tag index' });
  }

  const tag = file.tags[tagIndex]; // Safe: index is within bounds
  return response.send({ tag });
});

When using pagination with DynamoDB, always compute boundaries based on the actual result set rather than trusting Limit or ExclusiveStartKey values directly. For example, after a query, ensure slice indices are clamped to the returned items length:

const items = await queryDynamoItems(params);
const safeLimit = Math.min(Number(request.input('limit') || items.length, items.length);
const safeOffset = Math.max(Number(request.input('offset') || 0, 0);
const page = items.slice(safeOffset, safeOffset + safeLimit); // Safe slicing

Additionally, enforce schema validation using libraries like Joi to ensure attributes expected to be arrays are indeed arrays and contain expected element types. This prevents runtime surprises when DynamoDB returns NULL or missing attributes that would otherwise produce empty arrays and invalid indices.

Finally, leverage AdonisJS middleware to centralize input validation for API endpoints that interact with DynamoDB. This ensures consistent bounds checking across routes and reduces the likelihood of out-of-bounds reads due to overlooked edge cases in individual handlers.