Password Spraying in Aspnet

Password spraying attacks target Aspnet applications by attempting a small set of commonly used passwords against many usernames, avoiding account lockout thresholds. In Aspnet Core Identity, this often manifests against the /Account/Login endpoint when using default cookie authentication or JWT bearer tokens. Attackers enumerate valid usernames through response timing differences, error messages, or existing user discovery (e.g., via /api/users endpoints), then spray passwords like 'Password123!' or 'Welcome2024' across those accounts.

Aspnet-specific vulnerabilities arise when:

• Login endpoints return distinct HTTP status codes or messages for invalid username vs. invalid password (e.g., 404 for unknown user, 401 for bad password), enabling username enumeration.
• No password policy enforces complexity or breach-password checking, allowing weak passwords to remain valid.
• Authentication middleware lacks integrated brute-force or password-spraying throttling at the IP or account level.
• Legacy Aspnet Framework apps using FormsAuthentication may expose username validity via redirect behavior or error pages.

Real-world examples include CVE-2020-0609 (Azure AD password spray) and attacks on Aspnet Core apps where login pages leaked username existence via AJAX response headers. middleBrick detects this by analyzing login endpoint responses to invalid credentials and testing for username enumeration vectors during its Authentication and Input Validation checks.

Detecting password spraying in Aspnet requires observing authentication behavior under low-volume, high-distribution attack patterns. middleBrick’s black-box scanner identifies risk factors during its 5–15 second scan by:

• Testing the login endpoint with sequential username attempts using common passwords and measuring response variations (status codes, timing, error messages) to detect username enumeration.
• Checking for missing or weak password policy enforcement via AddIdentity options in Startup.cs or Program.cs when an OpenAPI spec is available (e.g., missing RequireNonAlphanumeric, RequiredLength < 8, or RequireDigit false).
• Validating absence of account lockout or password spray throttling (e.g., no MaxFailedAccessAttempts or DefaultLockoutTimeSpan configured in Identity options).
• Correlating findings with OWASP API Security Top 10 API1:2023 (Broken Object Level Authorization) and API7:2023 (Server Side Request Forgery) when username discovery occurs via other endpoints.

For example, if an Aspnet Core app’s login returns HTTP 200 with a generic error message for both invalid username and password, but the response body differs slightly (e.g., ‘Invalid username’ vs. ‘Invalid password’), middleBrick flags this as an Authentication risk. Similarly, if the OpenAPI spec reveals Identity services configured without lockout thresholds, it contributes to a lower security score in the Authentication category.

Mitigate password spraying in Aspnet applications using built-in Identity features and defensive coding practices:

1. Enable username enumeration protection: Configure Aspnet Core Identity to return identical responses for invalid username and password attempts. In Program.cs:

builder.Services.AddIdentity<IdentityUser, IdentityRole>(options =>
{
    options.SignIn.RequireConfirmedAccount = false;
    options.User.RequireUniqueEmail = false;
    // Prevent username enumeration via login errors
    options.SignIn.IncorrectPasswordSignInCountLockoutThreshold = 3;
    options.Lockout.DefaultLockoutTimeSpan = TimeSpan.FromMinutes(15);
    options.Lockout.MaxFailedAccessAttempts = 5;
    options.Lockout.AllowedForNewUsers = true;
})
.AddEntityFrameworkStores<ApplicationDbContext>();

Then, in the login handler, ensure SignInManager.PasswordSignInAsync is used without exposing failure reasons:

var result = await _signInManager.PasswordSignInAsync(Input.Email, Input.Password, Input.RememberMe, lockoutOnFailure: true);
if (result.IsLockedOut)
{
    _logger.LogWarning("User account locked out.");
    return RedirectToPage(&"/Account/Lockout");
}
else
{
    // Generic failure message regardless of username/password validity
    ModelState.AddModelError(string.Empty, "Invalid login attempt.");
    return Page();
}

2. Enforce strong password policies: Prevent weak passwords that spraying relies on:

builder.Services.AddIdentity<IdentityUser, IdentityRole>(options =>
{
    options.Password.RequireDigit = true;
    options.Password.RequireLowercase = true;
    options.Password.RequireUppercase = true;
    options.Password.RequireNonAlphanumeric = true;
    options.Password.RequiredLength = 12;
    options.Password.RequiredUniqueChars = 4;
});

3. Implement IP-based throttling for login endpoints: Use AspNetCoreRateLimit package to limit requests per IP:

builder.Services.AddMemoryCache();
builder.Services.Configure<IpRateLimitOptions>(options =>
{
    options.EnableEndpointRateLimiting = true;
    options.StackBlockedRequests = false;
    options.HttpStatusCode = 429;
    options.RealIpHeader = "X-Real-IP";
    options.GeneralRules = new List<RateLimitRule>
    {
        new RateLimitRule
        {
            Endpoint = "*POST*/api/account/login",
            Period = "5m",
            Limit = 5
        }
    };
});
builder.Services.AddSingleton<IIpPolicyStore>, MemoryCacheIpPolicyStore>();
builder.Services.AddSingleton<IRateLimitCounterStore>, MemoryCacheRateLimitCounterStore>();
builder.Services.AddSingleton<IRateLimitConfiguration>, RateLimitConfiguration>();
builder.Services.AddSingleton<IProcessingStrategy>, AsyncKeyLockProcessingStrategy>();
builder.Services.AddInMemoryRateLimiting();

These measures eliminate the low-and-slow spraying advantage by locking accounts after few failures, enforcing strong passwords, and blocking excessive login attempts per IP. middleBrick validates remediation by rescanning the endpoint and confirming uniform error responses, lockout behavior, and absence of username enumeration vectors.