Nosql Injection in Aspnet with Basic Auth

Nosql Injection occurs when an attacker can manipulate a NoSQL query by injecting malicious input. In an ASP.NET application using Basic Authentication, the combination of weak credential handling and unsanitized user input can expose the attack surface. Basic Auth transmits credentials in an easily decoded Base64 string; if the server does not enforce additional protections, attackers may leverage compromised or weak credentials to pivot into data-access layers that use NoSQL queries.

Consider an endpoint that retrieves user profiles by username. If the developer constructs a MongoDB query by directly concatenating user-supplied values, an attacker can alter the query logic. For example, sending username[$ne]: as the user portion of the Authorization header or as a form parameter can cause the backend to interpret it as a NoSQL injection vector. In ASP.NET, a vulnerable controller might look like this:

var username = Request.Form["username"];
var password = Request.Form["password"];
// Weak: directly embedding user input into a NoSQL query
var filter = Builders<BsonDocument>.Filter.Where(x => x["username"] == username);
var user = collection.Find(filter).FirstOrDefault();

An attacker could supply {"$ne": "" as the username, causing the filter to become {"username": {"$ne": ""}}, which returns all users. If Basic Auth is used without enforcing transport-layer encryption or additional validation, the injected query may bypass authentication checks or extract sensitive data. This scenario is especially risky when the same input is used both for authentication and for constructing NoSQL queries, effectively turning credential handling into a data-access channel.

ASP.NET applications that parse JSON payloads are also at risk. If a NoSQL query is built from deserialized objects without strict schema validation, an attacker can embed operators like $where, $regex, or $in into JSON fields that flow into the database layer. For instance, an attacker might send a crafted request where a nested object contains injection syntax, and if the server reflects or logs parts of the query, it may inadvertently disclose data or error messages that aid further exploitation.

Because middleBrick scans the unauthenticated attack surface, it can detect patterns such as unsanitized input flowing into NoSQL query construction. Findings often highlight the absence of input validation, improper credential handling, and missing query parameterization. Remediation guidance typically focuses on strict input validation, avoiding direct concatenation of user data into queries, and applying principle of least privilege to database connections.

Securing Basic Authentication in ASP.NET requires multiple layers of defense. First, never rely solely on Basic Auth for protecting sensitive operations; treat it as a transport-layer mechanism and always enforce HTTPS to prevent credential interception. Second, avoid using raw user input directly in NoSQL queries. Instead, use parameterized queries or an ORM with built-in safeguards, and validate input against a strict allowlist.

Below is a concrete, secure example of handling Basic Auth in ASP.NET Core that avoids exposing NoSQL injection vectors. The code parses credentials safely, validates them against a store, and uses parameterized queries:

using System.IdentityModel.Tokens.Jwt;
using System.Security.Claims;
using System.Text.Encodings.Web;
using Microsoft.AspNetCore.Authentication;
using Microsoft.AspNetCore.Authorization;
using Microsoft.AspNetCore.Mvc;
using MongoDB.Driver;

[ApiController]
[Route("api/[controller]")]
public class ProfileController : ControllerBase
{
    private readonly IMongoCollection<UserProfile> _profiles;

    public ProfileController(IMongoDatabase database)
    {
        _profiles = database.GetCollection<UserProfile>("profiles");
    }

    [HttpGet("{username}")]
    [Authorize]
    public async Task<ActionResult<UserProfile>> GetProfile(string username)
    {
        // Use the route/claim value rather than raw user input for queries
        var userIdentity = User.Identity as ClaimsIdentity;
        var claimUsername = userIdentity?.FindFirst(ClaimTypes.Name)?.Value;

        if (string.IsNullOrWhiteSpace(claimUsername) || claimUsername != username)
        {
            return Forbid();
        }

        // Parameterized query: username is passed as a filter value, not concatenated
        var filter = Builders<UserProfile>.Filter.Eq(p =>p.Username, username);
        var profile = await _profiles.Find(filter).FirstOrDefaultAsync();

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

        return Ok(profile);
    }
}

// Basic Auth handler (simplified)
public class BasicAuthHandler : AuthenticationHandler<AuthenticationSchemeOptions>
{
    private readonly IUserRepository _users;

    public BasicAuthHandler(
        IOptionsMonitor<AuthenticationSchemeOptions> options,
        ILoggerFactory logger,
        UrlEncoder encoder,
        ISystemClock clock,
        IUserRepository users)
        : base(options, logger, encoder, clock)
    {
        _users = users;
    }

    protected override async Task<AuthenticateResult> HandleAuthenticateAsync()
    {
        if (!Request.Headers.ContainsKey("Authorization"))
        {
            return AuthenticateResult.Fail("Missing Authorization Header");
        }

        var authHeader = Request.Headers["Authorization"].ToString();
        if (!authHeader.StartsWith("Basic ", StringComparison.OrdinalIgnoreCase))
        {
            return AuthenticateResult.Fail("Invalid Authorization Scheme");
        }

        var credentialString = Encoding.UTF8.GetString(Convert.FromBase64String(authHeader.Substring("Basic ".Length)));
        var credentials = credentialString.Split(':', 2);
        if (credentials.Length != 2)
        {
            return AuthenticateResult.Fail("Invalid Credentials Format");
        }

        var (inputUser, inputPass) = (credentials[0], credentials[1]);
        var user = await _users.FindByCredentialsAsync(inputUser, inputPass);
        if (user == null)
        {
            return AuthenticateResult.Fail("Invalid Credentials");
        }

        var claims = new[] { new Claim(ClaimTypes.Name, user.Username) };
        var identity = new ClaimsIdentity(claims, Scheme.Name);
        var principal = new ClaimsPrincipal(identity);
        var ticket = new AuthenticationTicket(principal, Scheme.Name);
        return AuthenticateResult.Success(ticket);
    }
}

Key points: the username used for the NoSQL query is derived from the authenticated principal, not directly from the request. This ensures that injection via the API payload cannot alter the intended filter. Additionally, always pair Basic Auth with HTTPS and consider short-lived tokens or additional factors for high-risk operations. middleBrick can verify that such patterns are in place by scanning endpoints and flagging unsanitized query construction.