Broken Access Control in Aspnet with Dynamodb

Broken Access Control (BOLA/IDOR) in an ASP.NET application using Amazon DynamoDB typically occurs when authorization checks are missing or incomplete before performing data operations. The risk is that an authenticated user can manipulate input—such as a record ID or partition key—to access or modify data belonging to other users. Because DynamoDB is a NoSQL data store, developers must enforce access controls at the application layer; the database itself does not provide row-level permissions based on user identity.

In ASP.NET, this often manifests in controller actions that accept an id or userId parameter, construct a DynamoDB key, and call GetItem or UpdateItem without verifying that the authenticated user is allowed to operate on that specific key. For example, an endpoint like /api/orders/{id} may retrieve the order from DynamoDB by primary key but fail to confirm the order belongs to the requesting user. Because DynamoDB requires you to explicitly provide the partition (and sort) key, incorrect or missing mapping between user identity and key attributes leads to direct IDOR: attacker-supplied keys return other users' data.

Additional risk patterns include insecure direct object references when using non-sequential or guessable identifiers (e.g., integer order IDs), and over-privileged IAM roles attached to the application that allow broad read/write access to the table. Attack chains can combine IDOR with other checks—such as missing rate limiting or insufficient input validation—to increase impact. For instance, an attacker might enumerate valid IDs, probe for horizontal privilege escalation, or combine IDOR with SSRF to reach internal metadata if the application uses DynamoDB metadata endpoints.

Using middleBrick’s scans, this class of issue is surfaced under the BOLA/IDOR check, which tests whether endpoints enforce proper ownership or authorization on each request. The scanner does not assume the database enforces permissions; it validates that every API interaction includes user-context checks before issuing DynamoDB operations.

Remediation centers on ensuring every DynamoDB operation is gated by explicit authorization that ties the request to the authenticated user. The following patterns demonstrate secure approaches for ASP.NET with the AWS SDK for .NET.

• Always derive the partition key from user identity rather than trusting client input. For example, if the table uses PK as the partition key and stores user-owned items under USER#{userId}, compute the key server-side and reject any client-supplied key that does not match.
• Use parameterized queries and avoid string concatenation that could lead to malformed keys.
• Apply row-level ownership checks after retrieving the item to double-check access, especially when using sparse indexes or secondary attributes for authorization.

Example 1: Secure GetItem with user-bound key

// GET /api/orders/{id} — ensure id maps to current user
[HttpGet("{id}")]
public async Task<IActionResult> GetOrder(string id)
{
    var userId = User.FindFirstValue(ClaimTypes.NameIdentifier);
    if (string.IsNullOrEmpty(userId))
        return Unauthorized();

    // Derive the partition key from user identity; do not trust {id} alone
    var key = new Dictionary<string, AttributeValue>
    {
        ["PK"] = new AttributeValue { S = $"USER#{userId}" },
        ["SK"] = new AttributeValue { S = $"ORDER#{id}" }
    };

    var request = new GetItemRequest
    {
        TableName = "AppTable",
        Key = key,
        // Optional: ProjectionExpression to limit returned attributes
        ProjectionExpression = "SK, SKU, Quantity, CreatedAt"
    };

    var response = await _dynamoDb.GetItemAsync(request);
    if (response.Item.Count == 0)
        return NotFound();

    // Additional server-side ownership check (defense in depth)
    if (!response.Item.TryGetValue("OwnerId", out var ownerAttr) || ownerAttr.S != userId)
        return Forbid();

    var order = new Order {
        Id = id,
        Sku = response.Item["SKU"].S,
        Quantity = int.Parse(response.Item["Quantity"].N),
        CreatedAt = DateTime.Parse(response.Item["CreatedAt"].S)
    };
    return Ok(order);
}

Example 2: Secure UpdateItem with scoped IAM and key derivation

// PATCH /api/orders/{id} — verify ownership before update
[HttpPatch("{id}")]
public async Task<IActionResult> UpdateOrder(string id, [FromBody] UpdateOrderDto dto)
{
    var userId = User.FindFirstValue(ClaimTypes.NameIdentifier);
    if (string.IsNullOrEmpty(userId))
        return Unauthorized();

    var key = new Dictionary<string, AttributeValue>
    {
        ["PK"] = new AttributeValue { S = $"USER#{userId}" },
        ["SK"] = new AttributeValue { S = $"ORDER#{id}" }
    };

    // Ensure the update does not change the partition key or owner
    var updateRequest = new UpdateItemRequest
    {
        TableName = "AppTable",
        Key = key,
        UpdateExpression = "set Quantity = :q, UpdatedAt = :u",
        ConditionExpression = "attribute_exists(PK) AND OwnerId = :owner",
        ExpressionAttributeValues = new Dictionary<string, AttributeValue>
        {
            [":q"] = new AttributeValue { N = dto.Quantity.ToString() },
            [":u"] = new AttributeValue { S = DateTime.UtcNow.ToString("o") },
            [":owner"] = new AttributeValue { S = userId }
        },
        // Return values on condition check failure for clearer errors
        ReturnValuesOnConditionCheckFailure = "ALL_OLD"
    };

    try
    {
        await _dynamoDb.UpdateItemAsync(updateRequest);
    }
    catch (ConditionalCheckFailedException)
    {
        return Forbid(); // Item does not belong to user or does not exist
    }

    return NoContent();
}

Example 3: Using policy-based authorization with resource-level checks

// Policy: UserMustOwnOrder — registered in Program.cs
// services.AddAuthorization(options => options.AddPolicy("UserMustOwnOrder", ...))
[HttpPut("{id}")]
[Authorize(Policy = "UserMustOwnOrder")]
public async Task<IActionResult> PutOrder(string id)
{
    // The policy handler resolves the item’s OwnerId from DynamoDB
    // and compares it to the user identifier; details omitted for brevity
    // Handler performs GetItem with key derived from {id} and user context
    // If check passes, controller proceeds; otherwise 403 is returned
    return Ok();
}

By combining route-to-key mapping, server-side key derivation, explicit ownership comparisons, and scoped IAM permissions, the ASP.NET + DynamoDB stack reduces the surface area for IDOR and BOLA attacks. middleBrick’s continuous monitoring and CI/CD integrations in the Pro plan can help detect regressions by scanning endpoints over time and failing builds when risk scores degrade.