Web.config implications of clearing sections? - asp.net

Question

I've come across code like this:
<modules>
<remove name="ScriptModule"/>
<remove name="YafTaskModule"/>
<remove name="UrlRewriter"/>
<add name="ScriptModule" preCondition="managedHandler" type="System.Web.Handlers.ScriptModule, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
<add name="YafTaskModule" type="YAF.Core.YafTaskModule, YAF.Core" preCondition="managedHandler"/>
<add name="UrlRewriter" type="Intelligencia.UrlRewriter.RewriterHttpModule,Intelligencia.UrlRewriter" preCondition="managedHandler"/>
</modules>
And it sometimes breaks, for example if your parent AppDomain doesn't have an UrlRewriter module in it, an error is raised.
How unsafe is it to use:
<modules>
<clear/>
<add name="ScriptModule" preCondition="managedHandler" type="System.Web.Handlers.ScriptModule, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
<add name="YafTaskModule" type="YAF.Core.YafTaskModule, YAF.Core" preCondition="managedHandler"/>
<add name="UrlRewriter" type="Intelligencia.UrlRewriter.RewriterHttpModule,Intelligencia.UrlRewriter" preCondition="managedHandler"/>
</modules>
Same happens in <httpModules> and a few other tags

Answer 1

The main issue with <clear /> is that it will clear all configured elements from all ancestor config files such as parent folder, machine level web.config and machine.config. So in case of <httpModules>, clearing will take out all essential ASP.NET modules such as authentication, session state management, output caching etc. In case your application depends on some of these modules then it will not work.
So the solution is that you must add those modules specifically after clearing the section which is actually correct solution for your problem. Downside is that your config file may become a bit verbose.