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From "Boyle Owen" <>
Subject RE: [users@httpd] Blocking invalid URIs?
Date Mon, 13 Mar 2006 07:49:40 GMT
> -----Original Message-----
> From: John Rodenbiker [] 
> Sent: Freitag, 10. März 2006 22:59
> To:
> Subject: [users@httpd] Blocking invalid URIs?
> I'm very new to running a web server.
> Is there a way to have httpd drop requests 

No. The HTTP RFC requires a server to respond to a valid HTTP request. It can respond with
an error (401, 403, 404 etc) but it must respond. [NB - a request for a resource you don't
have is a valid request].

>to URIs that don't 
> actually 
> exist in my environment?
> For example, if I have a very simple web site with just the document 
> "index.html" I don't want people trying to access 
> "../../../../../users/john/secretstuff". I would prefer such attempts 
> be dropped, logged, and an alert thrown to my mailbox or a 
> script that 
> calls my cell phone.

They'll be responded with a 403 Forbidden (assuming they land outside the docroot) and logged
in the access log and error log. You can define the ErrorDocument directive to run a program
when the error is hit (see docs for details) and that program can do what you like - send
mails, ring phones etc.  Do you really want your phone to ring ever time someone sends a funny

> If such functionality exists, is there a way for httpd to 
> automatically 
> figure out which URIs are valid and which are not without me 
> changing a 
> database, config file, etc. every time I update my site?

No. httpd is a webserver - it parses requests, fetches the resource and sends the data. The
only way you can figure out the extent of a website is by mirroring it. So you could run something
like wget on your site, make an image, then write a module that only allowed requests if the
resource was in the image (but that's what apache does anyway?) 

> It seems like this is an obvious way 

How is it obvious? What you are asking is, in parts, in violation of the RFC, impossible,
extremely difficult, performance-reducing and re-inventing the wheel.

>to prevent a host of 
> attacks on my 
> web server like 

> buffer-overflow attempts, 

Buffer overflows are identified and fixed by the guys in the white hats long before anyone
ever develops an exploit - keep up to date with patches and upgrades and you don't need to

> mis-configuration of the server, 

If you've misconfigured your server, your wget image will contain the misconfiguration so
will be allowed. UNless you define the image separately (ah - but you don't want to do that).

> cross-site scripting attacks,

Eh? This is java-script loaded into forum pages and so on... That's valid content. If you
don't want it, filter it at the form-handler.

To put your mind at ease, an up-to-date apache, with up-to-date components (OpenSSL, modules
etc) running on an up-to-date OS is a pretty solid proposition. Sure, you'll get lots of wierd
requests but they'll all end up in the bit-bucket and are nothing to worry about...

Owen Boyle
Disclaimer: Any disclaimer attached to this message may be ignored. 

> etc. I 
> just can't figure out where to look to turn this on and configure it.
> Thanks.
> -- 
> Freedom, Truth, Love, Beauty.
> John Rodenbiker
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