RE: Insecure Ids - Need explanation

["Patrick" <patrick () curioustechnology com>]

It's worded confusingly, but I think the point they're trying to get across
here is that if you have an easily guessable function- let's say you have a
web application that you notice has the following url:

http://www.example.com/default.asp?getContent

You later notice that you can get a specific piece of content with the next
url:

http://www.example.com/default.asp?getContentByContent?Id=23921


The naming convention is pretty easy to get a handle on here, and it's no
great leap of the imagination to see that you may be able to delete that
exact content with the following url:

http://www.example.com/default.asp?deleteContentByContentId?Id=23921


So if your application doesn't do a check to see that the caller is
authenticated for a given function, then anyone can perform that function.
Because there is a pretty common set of assumptions for managed web
applications with respect to design, you're likely to see attacks that will
be derivatives of this id guessing approach.  And ID's don't have to be
words- they could be numbers.  If they're based on a database's primary
keys, they're likely to be sequential, so once you've got one ID, you can
start looking for numbers within range of your that to tinker with.  

The moral of the story is: authenticate a user and then check for
authorization for your function calls.  Don't rely on obscure urls that can
only be found by clicking a certain page as the level of security needed for
keeping people out of administrative features on your applications.

-Patrick




-----Original Message-----
From: susam_pal () yahoo co in [mailto:susam_pal () yahoo co in] 
Sent: Monday, April 17, 2006 9:19 AM
To: webappsec () securityfocus com
Subject: Insecure Ids - Need explanation

This is an extract from OWASP.

Insecure Id's - Most web sites use some form of id, key, or index as a way
to reference users, roles, content, objects, or functions. If an attacker
can guess these id's, and the supplied values are not validated to ensure
the are authorized for the current user, the attacker can exercise the
access control scheme freely to see what they can access. Web applications
should not rely on the secrecy of any id's for protection. 

=================================================
Can anyone please elaborate this part,

"If an attacker can guess these id's, and the supplied values are not
validated to ensure the are authorized for the current user, the attacker
can exercise the access control scheme freely to see what they can access."

I have never used such ids, indexes or keys when I developed authentication
systems to reference users or roles. What kind of ids or keys are we talking
about? How can an attacker use a guessed id?

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