ASP.NET 4.6.1 Web Forms page 404 Issue

Question

I am working on a classic ASP website project and attempting to add a web form which will collect data from users and post that data to an API. My web app lives at wwwroot\\subdir\\myapp and I am targeting .NET framework 4.6.1 in the web.config. When I navigate to the site in the browser (mydomain.com\\subdir\\myapp or mydomain.com\\subdir\\myapp\\Default.aspx) it gives me a 404 error. If I reload once more, I receive a second 404 error. But, on the third load, the site loads all assets (JavaScript/HTML/CSS) without any errors in the browser console.

I checked the web server (IIS 8.5) logs, the first two loads are returning a 404.19 error. According to [1], this error indicates that IIS is denying the request for the page due to a filtering rule. But, if that is the case, why would it load on the third request?

[1] https://support.microsoft.com/en-us/help/943891/the-http-status-code-in-iis-7.0,-iis-7.5,-and-iis-8.0

Answer 1

Check security properties of website directory. There should be read access for user of Application pool. (Default is IUSR).

Answer 2

I figured out the issue. The URL is being parsed character by character and compared for an exact match to a list of keywords associated with SQL injection. The word that is causing my error is "update". I was able to figure out the solution by setting up a Failed Request Tracing rule in IIS Manager for .aspx requests.