Resolving HTTP Error 404.15 in ASP.NET Core MVC: Dealing with Long Query Strings

In the world of web development, encountering errors is inevitable. One such error that ASP.NET Core MVC developers might face is the HTTP Error 404.15 – Not Found. This error often occurs when the request filtering module is configured to deny requests with long query strings. While ASP.NET Core MVC projects don’t typically include a web.config file, resolving this issue requires a nuanced understanding of request filtering and configuration. In this blog post, we’ll delve into the root cause of this error and explore how to effectively fix it in ASP.NET Core MVC applications.

Understanding HTTP Error 404.15

HTTP Error 404.15 signifies that the request filtering module, often employed in IIS (Internet Information Services), is configured to reject requests where the query string exceeds a specified length. This limitation is imposed as a security measure to prevent certain types of attacks, but it can inadvertently lead to legitimate requests being rejected if the query string is too long.

Challenges in ASP.NET Core MVC

ASP.NET Core MVC projects differ from traditional ASP.NET projects in their approach to configuration. Unlike ASP.NET projects, ASP.NET Core MVC projects do not inherently include a web.config file for configuring IIS settings. This presents a challenge when attempting to address HTTP Error 404.15, as the typical solution involves modifying the web.config file.

Solution Approach

While ASP.NET Core MVC projects lack a web.config file by default, developers can still configure request filtering to address the issue of long query strings. The solution involves creating a web.config file in the project root directory and configuring request filtering settings within it. This file will be used by IIS when hosting the ASP.NET Core MVC application.

Configuring Request Filtering

To configure request filtering in an ASP.NET Core MVC application, follow these steps:

1. Create a new file named web.config in the root directory of the ASP.NET Core MVC project.
2. Add the necessary XML configuration to the web.config file to specify the desired request filtering settings, including the maximum query string length.
3. Adjust the maxQueryString attribute value according to the application’s requirements. This value determines the maximum allowed length of the query string in bytes.
4. Save the web.config file and ensure it is included in the project’s deployment package.

<?xml version="1.0" encoding="utf-8"?>
<configuration>
	<system.webServer>
		<security>
			<requestFiltering>
				<requestLimits maxQueryString="40000" />
			</requestFiltering>
		</security>
	</system.webServer>
</configuration>

Conclusion

HTTP Error 404.15 – Not Found can be a frustrating issue to encounter in ASP.NET Core MVC applications, particularly due to the absence of a web.config file by default. However, by understanding the root cause of the error and configuring request filtering appropriately, developers can effectively resolve this issue and ensure the smooth functioning of their applications. Implementing the solution outlined in this blog post enables ASP.NET Core MVC developers to handle long query strings gracefully, enhancing the security and reliability of their web applications.