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RE: Unsubscribe DoS

Many of these "unsubscribe" urls are just a way of verifying that the email
address is a valid one.  Probes, of a sort.

~~Ipsa scientia potestas est~~
~~Knowledge itself is power~~

-----Original Message-----
From: Frank Knobbe [mailto:frank@xxxxxxxxx] 
Sent: Thursday, December 19, 2002 12:35 AM
To: vuln-dev@xxxxxxxxxxxxxxxxx
Subject: Unsubscribe DoS


while reviewing postmasters email for a mail system we manage, I came across
an email from some list/spam server that offers an unsubscribe URL. This was
a bounced email for a user that no longer has a mail box on the systems. So
I just opened the browser and unsubscribed the user to avoid any further

Nice feature I thought..... and then I started to take a look at the URL
[1]. Obviously we have the subscriber ID (email recipient), the customer ID
(the client of the list/spam server), and the campaign ID (to identify the
mailing itself). 

The risk is that someone could just enter any subscriber ID and unsubscribe
someone else.

That made me wonder how widespread the problem is. Are there any pointers or
references to list/spam server opt-in/opt-out systems that are prone to
automated attacks, such as a for-loop posting http pages?