Cache Poisoning in Hapi with Dynamodb

Cache poisoning in a Hapi application that uses DynamoDB typically arises when an attacker can influence cached responses through manipulated inputs or headers, causing subsequent users to receive attacker-controlled data. Hapi’s caching layer may store responses based on request URLs, query parameters, or headers without adequately normalizing or validating inputs that eventually determine DynamoDB query behavior. If user-controlled values are directly reflected in cache keys or used to construct DynamoDB query parameters, an attacker can craft requests that cause different users to share the same cached response.

When combined with DynamoDB, risks emerge if the application builds query inputs from cache-derived or unvalidated parameters. For example, a cache key that incorporates a path or header value without canonicalization may allow an attacker to inject crafted identifiers that map to different DynamoDB items. If the Hapi route relies on a cached result that embeds a DynamoDB key condition derived from an attacker-influenced parameter, poisoned cache entries can expose data belonging to other users or bypass intended authorization boundaries. This can lead to sensitive data exposure or inconsistent authorization enforcement across cached responses.

DynamoDB’s attribute-based access patterns do not inherently prevent an application from misusing cached query inputs. If the server caches a response for a given set of query parameters that include an identifier tied to a DynamoDB partition key, an attacker who can manipulate those parameters may force the cache to store and serve another user’s data. Additionally, cache poisoning may interact with DynamoDB’s eventual consistency characteristics, where stale or malicious entries remain served until the cache expires, amplifying the window for data exposure. Proper input validation, cache key normalization, and separation of user context from cached keys are essential to mitigate these risks in Hapi with DynamoDB.

To reduce cache poisoning risks with DynamoDB in Hapi, ensure cache keys are deterministic, scoped to user and tenant context, and free from attacker-influenced values. Validate and sanitize all inputs used to construct DynamoDB query parameters, and avoid directly embedding raw user input in cache keys. Below are concrete code examples for a Hapi route that safely queries DynamoDB with cache-aware patterns.

// hapi-dynamodb-safe.js
'use strict';
const Hapi = require('@hapi/hapi');
const { DynamoDBClient, QueryCommand } = require('@aws-sdk/client-dynamodb');
const { marshall, unmarshall } = require('@aws-sdk/util-dynamodb');
const cache = new Map(); // simple in-memory cache for demonstration

const server = Hapi.server({ port: 4000, host: 'localhost' });

const ddbClient = new DynamoDBClient({ region: 'us-east-1' });

async function queryItemsByUserId(userId) {
  const command = new QueryCommand({
    TableName: 'UserItems',
    KeyConditionExpression: 'user_id = :uid',
    ExpressionAttributeValues: marshall({ ':uid': { S: userId } })
  });
  const resp = await ddbClient.send(command);
  return resp.Items ? unmarshall(resp.Items) : [];
}

server.route({
  method: 'GET',
  path: '/api/items/{userId}',
  options: {
    validate: {
      params: {
        userId: Joi.string().pattern(/^[a-zA-Z0-9_-]{1,64}$/).required()
      }
    },
    cache: {
      // scope cache to userId and tenant; avoid raw header/user input in key
      generateKey: (request) => {
        const tenantId = request.auth.credentials?.tenantId || 'unknown';
        return `items:${tenantId}:${request.params.userId}`;
      },
      expiresIn: 60_000,
      privacy: 'private'
    }
  },
  handler: async (request, h) => {
    const userId = request.params.userId;
    // ensure userId is canonicalized and safe before cache lookup
    const cacheKey = h.cache._generateKey(request);
    const cached = cache.get(cacheKey);
    if (cached) {
      return cached;
    }
    const items = await queryItemsByUserId(userId);
    cache.set(cacheKey, items);
    return items;
  }
});

(async () => {
  await server.start();
  console.log('Server running on %s', server.info.uri);
})();

In this pattern, the cache key is built from a tenant ID and the validated userId, avoiding inclusion of headers or other attacker-influenced values. Input validation enforces a strict pattern on userId, preventing injection of unexpected characters that could alter DynamoDB query behavior. The DynamoDB query uses the AWS SDK v3 marshalling to safely bind parameters, avoiding string concatenation that could lead to malformed keys or injection-like issues. For broader protection, apply similar validation and canonicalization across all routes, and ensure cache normalization rules align with your tenant and user boundaries.