Sql Injection in Aspnet with Dynamodb

SQL Injection is commonly associated with SQL databases, but injection concepts also apply when an ASP.NET application builds NoSQL queries unsafely, for example against DynamoDB. DynamoDB itself does not use SQL, yet client-side query construction can be vulnerable if user input is concatenated into key conditions, filter expressions, or pagination parameters without validation or parameterization.

In an ASP.NET context, a typical risk pattern is building a DynamoDB query in C# by string concatenation or interpolation using values from HTTP request parameters. Consider an endpoint that retrieves user data by username and a numeric user ID passed as query strings. If these values are directly embedded into a ScanCondition or a low-level QueryFilter, an attacker can supply crafted input that changes the intended semantics, such as bypassing tenant checks or extracting other users’ data.

For example, an attacker might provide username=' OR '1'='1 as the username parameter. If the application uses this value to build a condition like username = :username but the parameter binding is mishandled or concatenated incorrectly, the effective query could unintentionally match multiple partitions. Similarly, numeric IDs can be manipulated to traverse other records if access controls are not enforced server-side. This maps to common OWASP API Top 10 categories such as Broken Object Level Authorization (BOLA/IDOR) and Injection, and can lead to unauthorized data exposure.

DynamoDB’s low-level API and higher-level abstractions like the AWS SDK for .NET require explicit construction of expression attribute values and names. If an ASP.NET developer fails to consistently use parameters for these values, and instead interpolates strings into ScanCondition, QueryFilter, or raw JSON payloads, the application may expose a vector that allows injection-like behavior. The scanner’s checks for Input Validation and Property Authorization are designed to detect these insecure query-building patterns in unauthenticated scans, highlighting where user-controlled data reaches query construction without proper sanitization or authorization checks.

Another relevant pattern involves paginated or indexed queries where injection can manifest through crafted numeric offsets or inconsistent filter logic. For instance, an attacker might manipulate Limit or ExclusiveStartKey-related parameters to access unintended data ranges. Because DynamoDB does not have server-side parameterized SQL, the responsibility falls on the application to enforce strict validation, type checks, and authorization before issuing any query. middleBrick’s checks for BOLA/IDOR and Input Validation are particularly useful for identifying such risks in ASP.NET services that interact with DynamoDB.

To remediate injection risks when using DynamoDB from ASP.NET, always use the SDK’s built-in expression builders and parameter binding. Never concatenate user input into condition strings or filter expressions. Instead, use Expression and ScanCondition with explicit attribute values, and enforce authorization checks before invoking queries.

Secure DynamoDB query example in ASP.NET

The following example demonstrates a safer approach using the AWS SDK for .NET with parameterized expressions. It validates and binds user input via expression attribute values and uses a strict partition key lookup to enforce tenant isolation.

using Amazon.DynamoDBv2; 
using Amazon.DynamoDBv2.DocumentModel; 
using Amazon.DynamoDBv2.Model; 
using System; 
using System.Threading.Tasks; 
using Microsoft.AspNetCore.Mvc; 

[ApiController] 
[Route("api/users")] 
public class UsersController : ControllerBase 
{ 
    private readonly IAmazonDynamoDB _dynamoClient; 

    public UsersController(IAmazonDynamoDB dynamoClient) 
    {
        _dynamoClient = dynamoClient; 
    }

    [HttpGet] 
    public async Task<IActionResult> GetUserByUsername(string username, int userId) 
    { 
        // Basic input validation (extend with allowlist as appropriate)
        if (string.IsNullOrWhiteSpace(username) || userId <= 0) 
        { 
            return BadRequest("Invalid input."); 
        }

        var table = Table.LoadTable(_dynamoClient, "Users"); 

        var key = new Document(); 
        key["PartitionKey"] = $"USER#{username}"; 
        key["SortKey"] = $"PROFILE#{userId}"; 

        // Use GetItem for key-based retrieval (preferred over scan/query when possible)
        var config = new GetItemOperationConfig { ConsistentRead = true }; 
        var result = await table.GetItemAsync(key, config); 

        if (result == null) 
        { 
            return NotFound(); 
        } 

        // Enforce tenant/ownership check server-side even after key lookup
        var requesterTenant = GetTenantFromContext(); // implement your context logic
        if (result["TenantId"].AsString != requesterTenant) 
        { 
            return Forbid(); 
        } 

        return Ok(result); 
    }

    // Safer query using Expression for filter conditions (e.g., when querying GSI)
    public async Task<Search> SearchUsersByStatus(string usernamePrefix, string status) 
    { 
        var table = Table.LoadTable(_dynamoClient, "Users"); 

        var filter = new ScanCondition("Status", ScanOperator.Equal, status); 
        var searchConfig = new Search { Filter = filter, Limit = 100 }; 

        // Use parameterized expression for condition values
        var search = table.Scan(new[] { filter }); 
        var results = new List<Document>(); 
        do 
        { 
            var currentResults = await search.GetNextSetAsync(); 
            // Additional server-side authorization should be applied here
            results.AddRange(currentResults); 
        } while (!search.IsDone); 

        return new Search { Results = results }; 
    }

    private string GetTenantFromContext() 
    { 
        // Implement tenant extraction from claims, headers, or session
        return "tenant_abc"; 
    }
}

Key practices for DynamoDB in ASP.NET:

• Use GetItem for primary key lookups whenever possible; avoid scans and queries unless necessary.
• Always apply server-side authorization (e.g., compare tenant IDs) even after key-based retrieval.
• Validate and type-check all inputs (e.g., ensure numeric IDs are integers and within expected ranges).
• Prefer the Document Model or high-level abstractions with expression builders; avoid building raw JSON or concatenating strings for condition values.
• Leverage middleware or action filters for consistent input validation and tenant resolution across endpoints.

By combining strict input validation, parameterized SDK usage, and server-side authorization, you reduce the risk of injection-like issues and BOLA/IDOR problems in ASP.NET applications that use DynamoDB.