Identification Failures in Express with Dynamodb

Identification failures occur when an API incorrectly identifies or infers a user or resource identity, allowing one actor to act as another. In Express applications that use DynamoDB as the data store, this typically manifests as IDOR (Insecure Direct Object References) or BOLA (Broken Object Level Authorization). The combination is risky because DynamoDB is a low-level NoSQL store: it does not enforce identity policies itself, so authorization must be implemented in the application layer. If route parameters (e.g., :userId or :recordId) are used to directly form DynamoDB keys without verifying that the requesting user is allowed to access that specific key, an attacker can tamper with identifiers and read or modify other users' data.

DynamoDB’s key design amplifies this: primary keys (partition key, and optionally sort key) uniquely identify items. If an Express route accepts a userId path variable and uses it directly as the partition key value in a GetItem or Query request, an attacker can simply change the ID in the request to enumerate other users’ records. Because DynamoDB returns data when the key matches, and does not inherently understand application-level permissions, the burden falls on Express middleware to enforce ownership and authorization.

Common patterns that lead to identification failures include missing authorization checks between route resolution and DynamoDB calls, concatenating user input into key expressions without validation, and trusting identifiers provided in URLs or tokens without re-verifying scope. For example, an endpoint like GET /users/:userId/profile that runs docClient.get({ TableName: 'Users', Key: { userId: req.params.userId } }) without confirming that req.params.userId matches the authenticated subject enables IDOR. Attack tools or manual tampering can then iterate through plausible IDs to map other users’ data, a systematic exposure facilitated by the Express-to-DynamoDB integration lacking a robust authorization gate.

These failures also intersect with the broader set of 12 checks middleBrick runs in parallel. Identification failures map closely to the BOLA/IDOR and Property Authorization checks, and they can be surfaced in the report alongside findings from Input Validation and Authentication checks. Because DynamoDB does not provide built-in row-level security, developers must implement explicit authorization in Express, validating subject-to-resource relationships on every request. middleBrick’s scan can highlight missing authorization by correlating route parameters, IAM permissions used by the backend, and the presence of unverified direct key access patterns, helping teams identify identification flaws before they are exploited.

To remediate identification failures, enforce strict authorization before forming any DynamoDB key, and ensure that the subject from authentication is explicitly checked against the resource’s ownership attribute. Below are concrete Express patterns that integrate DynamoDB safely.

1. Enforce ownership check using the authenticated subject

Always resolve the authenticated user (e.g., from session or JWT) and compare it with the item’s owner attribute in DynamoDB. Do not trust route parameters alone.

import express from 'express';
import { DynamoDBClient, GetItemCommand } from '@aws-sdk/client-dynamodb';
import { unmarshall } from '@aws-sdk/util-dynamodb';

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

// Middleware to attach a resolved user (example via JWT)
app.use((req, res, next) => {
  const token = req.headers.authorization?.split(' ')[1];
  if (!token) return res.sendStatus(401);
  // decode and verify token; set req.user
  req.user = { id: 'user-123' }; // simplified example
  next();
});

app.get('/users/:userId/profile', async (req, res) => {
  const userIdFromRoute = req.params.userId;
  const currentUser = req.user?.id;

  if (!currentUser || userIdFromRoute !== currentUser) {
    return res.status(403).json({ error: 'Forbidden: cannot access other users’ profiles' });
  }

  const command = new GetItemCommand({
    TableName: 'Users',
    Key: {
      userId: { S: userIdFromRoute },
    },
  });

  try {
    const { Item } = await client.send(command);
    if (!Item) return res.sendStatus(404);
    res.json(unmarshall(Item));
  } catch (err) {
    console.error(err);
    res.status(500).json({ error: 'Internal server error' });
  }
});

2. Use conditional writes and expression attribute values for updates

When modifying items, ensure the request user owns the item by including a condition on the owner attribute. This prevents privilege escalation via tampered identifiers.

import { UpdateItemCommand } from '@aws-sdk/client-dynamodb';

app.patch('/users/:userId', async (req, res) => {
  const userIdFromRoute = req.params.userId;
  const currentUser = req.user?.id;

  if (userIdFromRoute !== currentUser) {
    return res.status(403).json({ error: 'Forbidden' });
  }

  const command = new UpdateItemCommand({
    TableName: 'Users',
    Key: {
      userId: { S: userIdFromRoute },
    },
    UpdateExpression: 'set displayName = :name',
    ConditionExpression: 'attribute_exists(userId) AND owner = :owner',
    ExpressionAttributeValues: {
      ':name': { S: req.body.displayName },
      ':owner': { S: currentUser },
    },
    ReturnValues: 'ALL_NEW',
  });

  try {
    const { Attributes } = await client.send(command);
    res.json(unmarshall(Attributes));
  } catch (err) {
    if (err.name === 'ConditionalCheckFailedException') {
      return res.status(409).json({ error: 'Conflict: item may not be owned or precondition failed' });
    }
    console.error(err);
    res.status(500).json({ error: 'Internal server error' });
  }
});

3. Prefer owner-indexed queries over direct key guesses

Instead of allowing clients to supply identifiers that map directly to keys, design endpoints that query by authenticated subject. For example, use a Global Secondary Index on owner or filter after fetching a small, authorized set.

import { QueryCommand } from '@aws-sdk/client-dynamodb';

app.get('/items', async (req, res) => {
  const ownerId = req.user?.id;
  if (!ownerId) return res.sendStatus(401);

  const command = new QueryCommand({
    TableName: 'Items',
    IndexName: 'owner-index',
    KeyConditionExpression: 'owner = :owner',
    ExpressionAttributeValues: {
      ':owner': { S: ownerId },
    },
  });

  try {
    const { Items } = await client.send(command);
    res.json(Items.map(unmarshall));
  } catch (err) {
    console.error(err);
    res.status(500).json({ error: 'Internal server error' });
  }
});

4. Validate and enforce identifier formats

Apply strict input validation on any identifier used in DynamoDB keys to prevent injection or malformed key errors. Use parameterized expressions and avoid concatenating raw strings into key objects.

import { z } from 'zod';

const userIdSchema = z.string().uuid(); // enforce UUID format

app.get('/users/:userId', async (req, res) => {
  const parsed = userIdSchema.safeParse(req.params.userId);
  if (!parsed.success) return res.status(400).json({ error: 'Invalid user ID format' });

  const command = new GetItemCommand({
    TableName: 'Users',
    Key: { userId: { S: parsed.data } },
  });
  // ... proceed as above
});

These patterns ensure that identification and authorization are explicit and enforced before any DynamoDB operation, reducing the risk of identification failures. middleBrick’s scans can surface missing authorization checks by correlating route parameters with DynamoDB key usage, helping teams prioritize fixes where user identity is incorrectly inferred.