c# - HTTP Error 414. The request URL is too long. asp.net

Question

I'm getting the error "HTTP Error 414. The request URL is too long." From the following article, I understand that this is due to a very long query string:

http://www.mytecbits.com/microsoft/iis/query-string-too-long

1. In web.config, I have maxQueryStringLength="2097151". Is this the maximum value?
2. In order to solve this problem, should I set maxUrl in web.config? If so, what's the maximum value supported?

What should I do to fix this error?

Answer 1

This error is actually thrown from http.sys, not from IIS. The error gets thrown before the request is passed along to IIS in the request-handling pipeline.

• To verify this, you can check the Server header value in the HTTP response headers, as per https://stackoverflow.com/a/32022511/12484.

To get https.sys to accept longer request URLs without throwing the HTTP 414 error, in the Windows Registry on the server PC, at ComputerHKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesHTTPParameters, create a DWORD-type value with name MaxFieldLength and value sufficiently large, e.g. 65535.

• Reference: Http.sys registry settings for Windows

If you decide to make this change, then obviously it’ll need to be made in all environments (including all production server(s)) -- not just on your local dev PC.

Also, whatever script and/or documentation your team uses to set up new server instances will need to be updated to include this registry setting, so that your team doesn’t forget to apply this setting 18 months from now when setting up a new production server.

Finally, be aware making this change could have adverse security consequences for all applications running on your server, as a large HTTP request submitted by an attacker won’t be rejected early in the pipeline as it would normally.

As an alternative to making this change to bypass the http.sys security, consider changing the request to accept HTTP POST instead of HTTP GET, and put the parameters into the POST request body instead of into a long URL. For more discussion on this, see question Design RESTful GET API with a long list of query parameters.