MSDN Documentation

Error Handling and Security

Effective error handling is crucial for maintaining the security posture of any application. Improperly managed error messages can inadvertently reveal sensitive information to attackers, leading to potential vulnerabilities.

Why Secure Error Handling Matters

Error messages are intended for developers and administrators to diagnose problems. However, if they are displayed directly to end-users or logged insecurely, they can provide attackers with:

• Details about the application's architecture.
• Information about the underlying operating system or database.
• Specific error codes that can be used to search for known exploits.
• Usernames, file paths, or other sensitive data.

Best Practices for Secure Error Handling

1. Avoid Verbose Error Messages to Users

Never expose detailed technical error information to the end-user. Instead, display generic, user-friendly messages. For example, instead of showing:

SQL Error: Column 'user_id' not found in table 'users'.
An unhandled exception occurred at line 42 of C:\project\data_access.php.

Display something like:

An unexpected error occurred. Please try again later. If the problem persists, please contact support.

2. Log Detailed Errors Securely

While users shouldn't see detailed errors, your application needs to capture them for debugging. Implement a robust logging mechanism that stores detailed error information in a secure location, accessible only to authorized personnel. Common information to log includes:

• Timestamp of the error.
• Error type and message.
• Stack trace.
• Relevant input parameters (sanitized if necessary).
• User ID or session information.

3. Implement Centralized Exception Handling

Use a global exception handler or a robust try-catch mechanism to catch unhandled exceptions. This allows you to standardize error reporting and logging across your application.

// Example in C#
public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    if (env.IsDevelopment())
    {
        app.UseDeveloperExceptionPage();
    }
    else
    {
        app.UseExceptionHandler("/Error"); // Redirect to a generic error page
    }
    // ...
}

// In your ErrorController (or similar)
[AllowAnonymous]
public IActionResult Error()
{
    var exceptionFeature = HttpContext.Features.Get();
    var exception = exceptionFeature?.Error;

    // Log the detailed exception here securely
    _logger.LogError($"Path: {exceptionFeature?.Path}, Error: {exception?.Message}, StackTrace: {exception?.StackTrace}");

    return View("GenericErrorView"); // A view with a generic message
}

4. Sanitize User Input

Many errors can be triggered by malicious or unexpected user input. Always validate and sanitize all incoming data before processing it to prevent common injection attacks that could lead to error conditions.

5. Use Specific Error Codes (Internally)

While not exposed to users, using specific, internal error codes can help developers quickly identify and resolve issues. These codes can be mapped to more general user-facing messages.

6. Handle Third-Party Library Errors

Errors originating from external libraries or services can also be a security risk. Ensure that these errors are caught, logged, and handled gracefully, without exposing the internals of the third-party component.

Example Scenario

Consider an authentication system. If a user enters an incorrect password, a secure system would:

1. Validate the input.
2. Check the username against the database.
3. Attempt to verify the password (without revealing if the username exists).
4. If authentication fails, return a generic "Invalid username or password" message to the user.
5. Log the failed login attempt (IP address, username, timestamp) securely for monitoring.

An insecure system might return specific messages like "User not found" or "Incorrect password," which can be exploited for username enumeration.