Auth Bypass in Restify with Dynamodb

Auth bypass in a Restify service that uses DynamoDB typically occurs when authorization checks are missing, incomplete, or incorrectly applied after authentication. Even when a request is authenticated (for example via an API key or JWT), the handler may fail to validate whether the authenticated principal has permission to access the specific DynamoDB resource. This mismatch between authentication and fine-grained authorization can allow an attacker to invoke endpoints and interact with DynamoDB items they should not see or modify.

Consider a Restify endpoint that retrieves user data by ID from DynamoDB. If the handler trusts an incoming identifier (such as userId) provided by the client and queries DynamoDB without confirming that the authenticated subject owns that ID, an authenticated attacker can enumerate or access other users’ records. This is often a BOLA/IDOR pattern in the context of DynamoDB, where missing ownership checks allow horizontal privilege escalation. A missing authorization layer on top of authentication means the API is effectively unauthenticated from a data-access perspective.

DynamoDB-specific factors can amplify the risk. Because DynamoDB is a NoSQL store, queries are often performed using key attributes such as userId and requestId. If the application builds queries by concatenating user input directly into the key expression without validating that the authenticated subject matches the requested key, an attacker can supply arbitrary IDs and read or overwrite items. For example, a handler that does params.KeyConditionExpression = 'userId = :uid' and binds :uid to req.params.userId without verifying that req.user.id equals req.params.userId will expose a clear authorization gap.

Another contributing factor is over-permissive IAM policies attached to the runtime role used by the service. If the role grants dynamodb:GetItem or dynamodb:Query on an entire table without scoping to a partition key prefix, a compromised application credential or an authenticated but malicious actor can read far more data than intended. Insecure table policies or cross-account roles can further widen the impact. These issues are detectable by security scanners that correlate IAM configurations with runtime behavior, highlighting where unauthenticated or insufficiently constrained access to DynamoDB coexists with exposed endpoints.

Because Restify APIs often integrate tightly with DynamoDB for low-latency data access, the combination of missing ownership validation, overly broad IAM permissions, and unchecked user-supplied keys creates a realistic path for unauthorized data access. The vulnerability is not inherent to Restify or DynamoDB individually, but emerges from the absence of rigorous authorization checks and least-privilege configurations in the integration layer.

Remediation centers on enforcing strict ownership checks and applying least-privilege access to DynamoDB. In Restify handlers, always derive the authorized subject from the authenticated context (e.g., req.user) and use it to constrain DynamoDB queries. Never trust client-supplied identifiers for data isolation.

Below is a concrete, secure Restify handler that demonstrates these principles. It verifies that the authenticated user matches the requested user ID and uses a parameterized DynamoDB query scoped to the partition key.

const restify = require('restify');
const AWS = require('aws-sdk');

const server = restify.createServer();
const docClient = new AWS.DynamoDB.DocumentClient({ region: 'us-east-1' });

server.get('/users/:userId', async (req, res, next) => {
  // Authentication should have already populated req.user (e.g., via JWT or API key validation)
  if (!req.user || !req.user.id) {
    return next(new restify.UnauthorizedError('Missing authentication'));
  }

  // Ensure the authenticated user matches the requested resource
  if (req.user.id !== req.params.userId) {
    return next(new restify.ForbiddenError('Access denied: insufficient permissions'));
  }

  const params = {
    TableName: process.env.USER_TABLE_NAME,
    KeyConditionExpression: 'userId = :uid',
    ExpressionAttributeValues: {
      ':uid': req.user.id  // Use authenticated identity, not user input
    }
  };

  try {
    const data = await docClient.query(params).promise();
    if (!data.Items || data.Items.length === 0) {
      return next(new restify.NotFoundError('User data not found'));
    }
    res.send(200, data.Items);
  } catch (err) {
    return next(new restify.InternalServerError(err.message));
  }
  return next();
});

server.listen(8080, () => {
  console.log('Server listening on port 8080');
});

This pattern ensures that the authenticated subject is used as the partition key value, preventing horizontal IDOR across users. For cases where a different principal-to-resource mapping exists (for example, orgId to resource), apply the same approach: bind the subject’s organization identifier into the key condition rather than using raw client input.

Complement code-level fixes with IAM and table policy hardening. The runtime role used by the service should be scoped to the least privilege necessary. For DynamoDB, prefer policies that restrict actions to specific table ARNs and include conditions that limit access based on partition key values when possible. Example IAM policy snippet:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": [
        "dynamodb:GetItem",
        "dynamodb:Query"
      ],
      "Resource": "arn:aws:dynamodb:us-east-1:123456789012:table/Users",
      "Condition": {
        "ForAllValues:StringEquals": {
          "dynamodb:LeadingKeys": ["${aws:userid}"]
        }
      }
    }
  ]
}

Such a policy ensures that even if credentials are leaked, the principal cannot query items outside their partition key scope. Combine this with regular scans of IAM policies and runtime behavior to detect over-permissive configurations early. The middleBrick CLI can be used to scan endpoints and surface missing authorization findings; the Pro plan adds continuous monitoring so changes to permissions or endpoints trigger reassessment, while the GitHub Action can fail builds if a new endpoint lacks required ownership checks. These integrations help maintain posture as APIs evolve.