Broken Access Control on Aws

Broken access control in Aws applications typically emerges from three distinct failure patterns. First, role-based authorization checks that fail to validate user permissions before executing sensitive operations. Second, cross-account resource access where AWS Identity and Access Management (IAM) policies are overly permissive or incorrectly scoped. Third, data filtering bypasses where API endpoints return all records regardless of the requesting user's ownership or permissions.

The most common Aws-specific manifestation occurs when developers rely on client-side filtering or assume that frontend controls prevent unauthorized access. Consider an application where users can view their own AWS resources but the backend API endpoint simply returns all resources without validating the caller's identity:

// Vulnerable: No authorization check
app.get('/api/aws/resources', async (req, res) => {
  const resources = await awsService.getAllResources();
  res.json(resources); // Returns all resources to any authenticated user
});

This pattern becomes particularly dangerous in multi-tenant Aws environments where users might access each other's AWS configurations, CloudFormation stacks, or Lambda functions.

Another prevalent Aws-specific issue involves improper IAM role assumption. Applications often use AWS STS to assume roles for accessing different AWS services, but fail to validate whether the current user has permission to assume those roles:

// Vulnerable: Any authenticated user can assume any role
const assumeRole = async (req, res) => {
  const roleArn = req.body.roleArn; // No validation
  const credentials = await sts.assumeRole({
    RoleArn: roleArn,
    RoleSessionName: 'assumed-role'
  }).promise();
  res.json(credentials);
};

Cross-account access vulnerabilities also plague Aws applications. When organizations use AWS Organizations or multiple accounts, applications might expose endpoints that allow users to query resources across accounts without proper authorization:

// Vulnerable: No cross-account authorization
app.get('/api/organizations/accounts', async (req, res) => {
  const accounts = await organizations.listAccounts();
  res.json(accounts); // Returns all organization accounts
});

Property-level authorization failures are another Aws-specific concern. Applications often expose detailed AWS resource information through APIs but fail to filter sensitive properties like IAM role ARNs, security group configurations, or VPC details:

// Vulnerable: Exposes all resource properties
app.get('/api/aws/vpcs', async (req, res) => {
  const vpcs = await ec2.describeVpcs().promise();
  res.json(vpcs); // Returns complete VPC objects including sensitive metadata
});

Detecting broken access control in Aws applications requires both static analysis of authorization logic and dynamic testing of API endpoints. The most effective approach combines automated scanning with manual verification of critical access paths.

middleBrick's black-box scanning approach is particularly effective for Aws applications because it tests the actual running API without requiring source code access. The scanner automatically identifies Aws-specific endpoints by analyzing request patterns, response structures, and API documentation. When scanning an Aws management application, middleBrick looks for:

• Authentication bypass attempts on Aws-specific endpoints
• Resource enumeration across different user contexts
• Property exposure in Aws resource responses
• IAM role assumption vulnerabilities
• Cross-account access patterns
• Data filtering bypasses in Aws resource queries

The scanner tests these patterns by creating multiple test accounts with different permission levels and attempting to access resources across those contexts. For example, it might create a user with read-only Aws permissions and attempt to modify resources, or create a user in one AWS account and attempt to access resources in another account.

Manual detection should focus on Aws-specific authorization patterns. Review your application's use of AWS SDK methods and verify that each operation includes proper authorization checks. Pay special attention to:

// What to check for in your code
const checkAuthorization = (user, resource) => {
  // Verify user owns this resource
  if (user.accountId !== resource.accountId) {
    throw new Error('Access denied');
  }
  // Verify user has required permissions
  if (!user.permissions.includes('read:' + resource.type)) {
    throw new Error('Insufficient permissions');
  }
};

Look for patterns where Aws SDK calls are made without corresponding authorization validation. Common red flags include direct calls to describeVpcs, listFunctions, or listStacks without checking whether the current user should have access to those resources.

middleBrick's OpenAPI analysis feature is particularly valuable for Aws applications because it can cross-reference your API specification with runtime behavior. The scanner validates that your documented endpoints match the actual authorization requirements and identifies discrepancies where endpoints claim to be secure but lack proper access controls.

Remediating broken access control in Aws applications requires a defense-in-depth approach that combines proper IAM configuration, application-level authorization, and data filtering. The foundation is implementing the principle of least privilege at both the AWS service level and application logic level.

Start with IAM policy configuration. Use IAM roles and policies to enforce access boundaries at the AWS service level:

// IAM policy example - least privilege approach
const iamPolicy = {
  Version: '2012-10-17',
  Statement: [
    {
      Effect: 'Allow',
      Action: [
        'ec2:DescribeVpcs',
        'ec2:DescribeSubnets'
      ],
      Resource: 'arn:aws:ec2:*:*:vpc/*'
    },
    {
      Effect: 'Deny',
      Action: 'ec2:*',
      Resource: 'arn:aws:ec2:*:*:vpc/*',
      Condition: {
        StringNotEquals: {
          'ec2:ResourceTag/Owner': '${aws:username}'
        }
      }
    }
  ]
};

Application-level authorization should validate user permissions before any AWS SDK call. Implement a centralized authorization middleware:

// Authorization middleware for Aws applications
const authorizeAwsResource = async (req, res, next) => {
  const { resourceType, resourceId } = req.params;
  const user = await getUserFromToken(req.headers.authorization);
  
  // Check if user owns this resource
  const resource = await getResourceOwnership(resourceType, resourceId);
  if (!resource || resource.ownerId !== user.id) {
    return res.status(403).json({ error: 'Access denied' });
  }
  
  // Check user permissions for this resource type
  const allowedActions = await getUserPermissions(user.id, resourceType);
  const requiredAction = req.method === 'GET' ? 'read' : 'write';
  
  if (!allowedActions.includes(requiredAction)) {
    return res.status(403).json({ error: 'Insufficient permissions' });
  }
  
  next();
};

For cross-account Aws applications, implement strict account isolation. Never allow direct cross-account resource access without explicit user consent and additional authorization:

// Cross-account access with explicit authorization
const crossAccountAccess = async (req, res) => {
  const { targetAccountId, resourceType, resourceId } = req.body;
  const user = await getUserFromToken(req.headers.authorization);
  
  // Verify user has cross-account permission
  if (!user.permissions.includes('cross-account-access')) {
    return res.status(403).json({ error: 'Cross-account access not permitted' });
  }
  
  // Verify explicit consent for this specific account access
  const consent = await getCrossAccountConsent(user.id, targetAccountId);
  if (!consent || !consent.active) {
    return res.status(403).json({ error: 'Cross-account consent required' });
  }
  
  // Perform the cross-account operation with proper IAM role assumption
  const credentials = await sts.assumeRole({
    RoleArn: `arn:aws:iam::${targetAccountId}:role/CrossAccountReader`,
    RoleSessionName: `user-${user.id}`
  }).promise();
  
  // Use temporary credentials for the cross-account operation
  const client = new AWS.STS({ credentials });
  // ... perform operation
};

Data filtering is critical for Aws applications that return resource lists. Never return complete resource objects without filtering based on user permissions:

// Proper data filtering for Aws resource endpoints
app.get('/api/aws/resources', async (req, res) => {
  const user = await getUserFromToken(req.headers.authorization);
  
  // Get only resources the user owns or has access to
  const resources = await awsService.getResourcesByUser(user.id);
  
  // Filter sensitive properties
  const filteredResources = resources.map(resource => {
    return {
      id: resource.id,
      name: resource.name,
      type: resource.type,
      // Exclude sensitive metadata like IAM roles, security groups, etc.
    };
  });
  
  res.json(filteredResources);
});